RAIDING different size drives

[Sydney Lambe]

I want to mirror 2 disks mirror using RAID.

Can this be done on a 750GB and 500GB disk?

It's a single user desktop running XP with RAID provided by a PCI card.
Might change the mobo to one with RIAD if it's better?

This is for editing audio. Don't want to lose audio work if a disk fails
so RAID looks right.

 

[Arno]

I want to mirror 2 disks mirror using RAID.

Can this be done on a 750GB and 500GB disk?

Typically, yes. In practive there mey be controllers that
cannot handle the larger disk at all, but mixing is not
an issue, as long as disks added later (as replacement)
are the same size or larger. On createion you can have
any mix.

It's a single user desktop running XP with RAID provided by a PCI card.
Might change the mobo to one with RIAD if it's better?

Depends. You also need to be aware that with hardware RAID you
need a spare controller to get at your data if the controller
fails. (There are other ways, e.g. with Linux, but they
require a certain expertise). With RAID1 it may also be possible
to access each individual disk directly on a non-RAID controller,
but you should test that to make sure.

This is for editing audio. Don't want to lose audio work if a disk fails
so RAID looks right.

It does. But only for disk failures. Software and udser failures
are not covered. Also things that destroy both disks (fire, lightening,
burglary, etc..) are not coverd as well. RAID is not backup!

Arno

 

[David Brown]

I want to mirror 2 disks mirror using RAID.

Can this be done on a 750GB and 500GB disk?

It's a single user desktop running XP with RAID provided by a PCI card.
Might change the mobo to one with RIAD if it's better?

This is for editing audio. Don't want to lose audio work if a disk fails
so RAID looks right.

I believe that with a hardware RAID solution (and I think that also
applies to pretend hardware RAID that is often supported by motherboards
and cheap cards), you have to use whole disks in the RAID. That means
the 750 GB disk will be treated as 500 GB to make the mirroring work.

If you use software raid, you can do it on a partition level - use 250GB
of the 750 GB for the OS, software, swap, etc., and use a 500 GB
partition for mirroring with a matching partition on the other disk.

Of course, the idea of software RAID on windows to improve reliability
is an oxymoron. Use RAID on a windows machine to improve speed, but if
your data is important then save it regularly on a reliable system.
File system corruption, due to Windows itself or to malware running on
the system, far outweighs the risk of hardware disk failures (though
corruption may affect only some files, while hardware failure can affect
the whole disk). And when Windows or malware mucks up your file system,
your RAID 1 setup ensures that the same errors are copied over to the
mirrored drive.

In short, RAID can improve speed and/or uptime, but it does not
noticeably improve data security, and it is not a substitute for backups.

 

[Rod Speed]

David Brown wrote

Sydney Lambe wrote

I believe that with a hardware RAID solution (and I think that also applies to pretend hardware RAID that is often
supported by motherboards and cheap cards), you have to use whole disks in the RAID. That means the 750 GB disk will
be treated as 500 GB to make the mirroring work.

Yes, but not all of them will handle that pair.

If you use software raid, you can do it on a partition level - use 250GB of the 750 GB for the OS, software, swap,
etc., and use a 500 GB
partition for mirroring with a matching partition on the other disk.

Of course, the idea of software RAID on windows to improve reliability is an oxymoron.
Wrong.

Use RAID on a windows machine to improve speed, but if your data is important then save it regularly on a reliable
system.

Or use mirroring to improve the reliability.

File system corruption, due to Windows itself or to malware running on the system, far outweighs the risk of hardware
disk failures
Wrong.

(though corruption may affect only some files, while hardware failure can affect the whole disk).

Mangled all over again.

And when Windows or malware mucks up your file system, your RAID 1 setup ensures that the same errors are copied over
to the mirrored drive.

Just as true of any other OS.

In short, RAID can improve speed and/or uptime, but it does not noticeably improve data security,
Wrong.

and it is not a substitute for backups.

But does give added protection against the failure of a drive.

 

[David Brown]

David Brown wrote


Yes, but not all of them will handle that pair.

Fair enough - I don't have much experience with hardware raid cards, so
I don't know the details of their capabilities.

Wrong.

It would have been more accurate of me to say "on a windows desktop".

This is perhaps not the group for discussing OS reliability, but from my
own experience (running IT for a small company for many years) and from
endless accounts on the web, windows is generally an inferior choice of
OS for solid and reliable storage. Factors that improve the reliability
(regardless of the OS) are better hardware (desktops are typically fast
but poorer reliability), server usage rather than desktop usage (fewer
programs, with more limited scope and more testing), higher security
(avoiding malware or attacks), and better environment (such as UPS for
power, cooled server room, no spilled coffee, etc.)

You don't store files on a windows desktop and expect it to be
"reliable". You store your important files on a server (preferably on a
non-Windows system). You keep good backups, whether you have a server
or not. If all you have is a windows desktop with typical usage
patterns, then using raid, especially windows software raid, is a such
minor step towards reliability that it's not worth considering until
you've looked at the system as a whole. An external harddisk which you
plug in, take backups, and unplug on a regular basis would do far more
to protect the safety of the data files than mirroring the internal hard
disk.

Or use mirroring to improve the reliability.


Wrong.

I've seen a fair number of computers through the years, and I have very
seldom seen physical hard disk failures. I *have* seen plenty of
corrupted disks, and I have helped out people with malware on many
occasions. Mirroring just means you have two copies of the corrupted
file systems.

I should of course have mentioned the biggest cause of data loss - user
error. Again, mirroring is useless against this, while a good backup
regime gives protection.

Mangled all over again.


Just as true of any other OS.

Absolutely - and other OS's are not immune to either malware, attacks,
or file system corruption. But they are (assuming they are configured
and administered properly) orders of magnitude lower risk. The same
applies to server usage rather than desktop usage, regardless of OS - it
hugely lowers your risks of malware or corruption.

But does give added protection against the failure of a drive.

Yes, but hardware failure is such a tiny risk compared to everything
else, that it's not worth bothering about until everything else is in place.

If you have two hard disks in a desktop machine and you want to improve
reliability for your data files, you format the second disk as a
separate partition labelled "backups". You take regular copies of your
data files from your working disks into separate directories on the
backup disk (there are many ways to organise this, but that's a topic
for another thread). This protects against user error, against most
corruption (you are unlikely to corrupt the two independent file
systems), and gives reasonable protection against hardware failure (if
your main drive dies, you'll have to re-install your OS and software on
a new disk, but your data is safe).


Another thing to consider is your access to the files in the case of
operating system death, which is not exactly uncommon on desktop windows
systems. In such cases, your data is safe on the disk, but the windows
registry or critical files are corrupted. Windows will do this on its
own occasionally, especially if provoked (such as by power failures),
and third-party "security" software updates are notorious for rendering
windows unbootable. And of course, malware of all sorts can similarly
render the machine useless.

How do you then get your data files off the broken system, before trying
to fix it or to use a "system restore" CD that deletes all your data?
Ideally, you use the copies that are on a server, or your backup copies.
If you've got a second copy on an independent hard disk, you can use
that disk in another machine, or remove it until you've fixed the main
drive. You can also use a live Linux CD and access the files that way.
But if everything is on a raid setup, you don't have an independent
way to access the data. Maybe a live Linux CD will be able to access
the data, maybe not.

 

[Arno]

I believe that with a hardware RAID solution (and I think that also
applies to pretend hardware RAID that is often supported by motherboards
and cheap cards), you have to use whole disks in the RAID. That means
the 750 GB disk will be treated as 500 GB to make the mirroring work.

Well, yes. Rather obvious, I would think.

If you use software raid, you can do it on a partition level - use 250GB
of the 750 GB for the OS, software, swap, etc., and use a 500 GB
partition for mirroring with a matching partition on the other disk.

One of the reasons I prefer software RAID...

Of course, the idea of software RAID on windows to improve reliability
is an oxymoron.

.... on Linux. I have heard though that for the "professionsl"
windows versions, software RAID works reasonably well.

Use RAID on a windows machine to improve speed, but if
your data is important then save it regularly on a reliable system.
File system corruption, due to Windows itself or to malware running on
the system, far outweighs the risk of hardware disk failures (though
corruption may affect only some files, while hardware failure can affect
the whole disk). And when Windows or malware mucks up your file system,
your RAID 1 setup ensures that the same errors are copied over to the
mirrored drive.

You still need backup with RAID. That is not a problem limited to
Windows.

In short, RAID can improve speed and/or uptime, but it does not
noticeably improve data security, and it is not a substitute for backups.

It does nothing for security, it improves reliability. However
it does indeed not cover everything you do backups for, so
you still need them.

Arno

 

[Arno]

Fair enough - I don't have much experience with hardware raid cards, so
I don't know the details of their capabilities.

As I wrote, the card needs to be able tho handle the disk size
of all used disks.

It would have been more accurate of me to say "on a windows desktop".

This is perhaps not the group for discussing OS reliability, but from my
own experience (running IT for a small company for many years) and from
endless accounts on the web, windows is generally an inferior choice of
OS for solid and reliable storage. Factors that improve the reliability
(regardless of the OS) are better hardware (desktops are typically fast
but poorer reliability), server usage rather than desktop usage (fewer
programs, with more limited scope and more testing), higher security
(avoiding malware or attacks), and better environment (such as UPS for
power, cooled server room, no spilled coffee, etc.)

Interestingly my current employer uses Linux software RAID for
the base system and then puts Windows installations in VMWare
on top of that. This works pretty well, but requires people that
understand Linux and Windows.

You don't store files on a windows desktop and expect it to be
"reliable". You store your important files on a server (preferably on a
non-Windows system). You keep good backups, whether you have a server
or not. If all you have is a windows desktop with typical usage
patterns, then using raid, especially windows software raid, is a such
minor step towards reliability that it's not worth considering until
you've looked at the system as a whole. An external harddisk which you
plug in, take backups, and unplug on a regular basis would do far more
to protect the safety of the data files than mirroring the internal hard
disk.

I agree. There is a cultural difference. Unix folks expect their
stuff to reside on servers, be backed up by the system administrator,
etc.. If they operate their own (say) Linux box, they do all that
by themselves, because they regard it as part of professional
computing. The MS crowd comes out of the "computing is easy"
crows that then sometimes becomes the "where has all my data
gone" crowd.

But even the more knowledgeable MS users tend to use
servers with system administrators today.

I've seen a fair number of computers through the years, and I have very
seldom seen physical hard disk failures. I *have* seen plenty of
corrupted disks, and I have helped out people with malware on many
occasions. Mirroring just means you have two copies of the corrupted
file systems.

I habve seen a number of disk failures. I have run about 50 drives
in a climate controlled server room for 4 years, with maybe one
unexplained failure (the others were dropped in shipping). I have
seen a RAID1 of Maxtors fail from heat (helped the colleguae that
set this up to recover some data). I have seen a lot of
DeathStars die, including 2/2 of my own. I also have one 2.5"
HDD in a RAID1 that has a tendency to transient errors. It drops
out of the RAID about 2-3 times a year.

I agree that for well handled disks under good operating
conditions fail rarely, and in line with the manufacturer-stated
reliability. However many desktop systems do not provide
these conditions. And there can be surprises, like the DeathStars
or the exceedingly heat-sensitive Maxtors of some years ago.

I should of course have mentioned the biggest cause of data loss - user
error. Again, mirroring is useless against this, while a good backup
regime gives protection.

Agreed. And it helps to use version control systems and rotating
or incremental automatic backups to other systems.

Absolutely - and other OS's are not immune to either malware, attacks,
or file system corruption. But they are (assuming they are configured
and administered properly) orders of magnitude lower risk. The same
applies to server usage rather than desktop usage, regardless of OS - it
hugely lowers your risks of malware or corruption.

Indeed. Wirh a Unix/Linys system, you need to be scared maybe
a year or so. With Windows, you need to be scared half of the time.

Yes, but hardware failure is such a tiny risk compared to everything
else, that it's not worth bothering about until everything else is in place.

I do not agree. RAID1 is cheap, especially as software RAID.

If you have two hard disks in a desktop machine and you want to improve
reliability for your data files, you format the second disk as a
separate partition labelled "backups". You take regular copies of your
data files from your working disks into separate directories on the
backup disk (there are many ways to organise this, but that's a topic
for another thread). This protects against user error, against most
corruption (you are unlikely to corrupt the two independent file
systems), and gives reasonable protection against hardware failure (if
your main drive dies, you'll have to re-install your OS and software on
a new disk, but your data is safe).

Well, this is one approach. What I do is have RAID and do copies to
other partitions. Except for Windows, there I just have backup.

Another thing to consider is your access to the files in the case of
operating system death, which is not exactly uncommon on desktop windows
systems. In such cases, your data is safe on the disk, but the windows
registry or critical files are corrupted. Windows will do this on its
own occasionally, especially if provoked (such as by power failures),
and third-party "security" software updates are notorious for rendering
windows unbootable. And of course, malware of all sorts can similarly
render the machine useless.

One of the reasons I regard Windows as a "toy". Wit Linux/FreeBSD/...
I can just backup/move/restore an application directory and
things will work. No single-point-of-failure monstrosity like
the registry. But there is well-programmed Windows software that
does not need/use the registry. For example, you can copy the World
of Warcraft installation directory to an entirely different machine
and it works there too. Unfortunatrly, not many of the software
defelopers on the MS platform "get it". One of the cultural
disadvantages.

How do you then get your data files off the broken system, before trying
to fix it or to use a "system restore" CD that deletes all your data?

These are a cruel joke IMO!

Ideally, you use the copies that are on a server, or your backup copies.
If you've got a second copy on an independent hard disk, you can use
that disk in another machine, or remove it until you've fixed the main
drive. You can also use a live Linux CD and access the files that way.
But if everything is on a raid setup, you don't have an independent
way to access the data. Maybe a live Linux CD will be able to access
the data, maybe not.

If it is a Linux software RAID, it will. Otherwise dm-raid may help.
But you absolutely need to test this before you have a problem.

Arno

 

[Rod Speed]

David Brown wrote

Rod Speed wrote

Fair enough - I don't have much experience with hardware raid cards, so I don't know the details of their
capabilities.

It would have been more accurate of me to say "on a windows desktop".

Still wrong. You do get extra protection against a hard drive failure.

This is perhaps not the group for discussing OS reliability,

Its fine for that.

but from my own experience (running IT for a small company for many years)

Mine leaves yours for dead.

and from endless accounts on the web, windows is generally an inferior choice of OS for solid and reliable storage.

Irrelevant to that silly claim that RAID 1 gains you nothing with Win.

And it isnt even an oxymoron either.

Factors that improve the reliability (regardless of the OS) are better hardware (desktops are typically fast but
poorer reliability),

Thats just plain wrong too.

server usage rather than desktop usage (fewer programs, with more limited scope and more testing), higher security
(avoiding malware or attacks), and better environment (such as UPS for power, cooled server room, no spilled coffee,
etc.)

Waffle.

RAID 1 does give better protection against hard drive failure even with Win.

You don't store files on a windows desktop and expect it to be "reliable".

Irrelevant to whether RAID 1 is more reliable than not using RAID 1 or mirroring.

You store your important files on a server (preferably on a non-Windows system).

No need to do that if you have adequate backups.

You keep good backups, whether you have a server or not.

And if you do that, you dont need a server.

If all you have is a windows desktop with typical usage patterns, then using raid, especially windows software raid,
is a such
minor step towards reliability that it's not worth considering until
you've looked at the system as a whole.

Irrelevant to your silly claim that mirroring adds nothing to reliability.

An external harddisk which you plug in, take backups, and unplug on a regular basis would do far more to protect the
safety of the data files than mirroring the internal hard disk.

Mirroring STILL improves reliability, most obviously
when a hard drive fails between backups.

I've seen a fair number of computers through the years,

I've seen a lot more than you have.

and I have very seldom seen physical hard disk failures.

Yes, but that doesnt alter the fact that they do fail.

I *have* seen plenty of corrupted disks,

I havent seen any more corrupted by Win than I have seen that have failed.

and I have helped out people with malware on many occasions.

No one ever said that mirroring helps with all problems.

Mirroring just means you have two copies of the corrupted file systems.

And helps when a hard drive fails.

I should of course have mentioned the biggest cause of data loss - user error.

Irrelevant to whether mirroring does help with hardware failure.

Again, mirroring is useless against this, while a good backup regime gives protection.

No one ever said that mirroring is a substitute for backups.

Absolutely - and other OS's are not immune to either malware, attacks, or file system corruption.

And user error in spades.

But they are (assuming they are configured and administered properly) orders of magnitude lower risk.

Pig ignorant lie.

The same applies to server usage rather than desktop usage, regardless of OS - it hugely lowers your risks of malware
or corruption.

Irrelevant to whether mirroring does improve reliability.

Yes, but hardware failure is such a tiny risk compared to everything
else, that it's not worth bothering about until everything else is in place.

Thats just plain wrong with everything except backups.

If you have two hard disks in a desktop machine and you want to improve reliability for your data files, you format
the second disk as a separate partition labelled "backups". You take regular copies of your data files from your
working disks into separate directories on the backup disk

There are much better ways to do backup than that.

(there are many ways to organise this, but that's a topic for another thread).
Nope.

This protects against user error, against most corruption (you are unlikely to corrupt the two independent file
systems), and gives reasonable protection against hardware failure (if your main drive dies, you'll have to re-install
your OS and software on a new disk, but your data is safe).

There are much better ways to do backup than that.

<reams of you trying to teach your granny to suck eggs flushed where it belongs>

 

[David Brown]

Interestingly my current employer uses Linux software RAID for
the base system and then puts Windows installations in VMWare
on top of that. This works pretty well, but requires people that
understand Linux and Windows.

It requires IT administrators that understand both Linux and Windows
(and these days, most IT departments of any size should understand
both). Users, for the most part, should be kept blissfully ignorant of
which machines are "real", and which are "virtual", and what OS they are
running.

I agree. There is a cultural difference. Unix folks expect their
stuff to reside on servers, be backed up by the system administrator,
etc.. If they operate their own (say) Linux box, they do all that
by themselves, because they regard it as part of professional
computing. The MS crowd comes out of the "computing is easy"
crows that then sometimes becomes the "where has all my data
gone" crowd.

But even the more knowledgeable MS users tend to use
servers with system administrators today.

I think in most companies, most data is held on centralised servers even
if the network is entirely Windows based - although there's always some
users that save things under "My Documents", or use POP3 email. IT
administrators don't like it when users do that - because they get the
job of finding the lost data again.

For smaller companies and home networks, then I agree there is a
definite cultural difference. People use old PC's running Linux as home
servers for their email and files - very few think of buying and
installing a Windows server.

I habve seen a number of disk failures. I have run about 50 drives
in a climate controlled server room for 4 years, with maybe one
unexplained failure (the others were dropped in shipping). I have
seen a RAID1 of Maxtors fail from heat (helped the colleguae that
set this up to recover some data). I have seen a lot of
DeathStars die, including 2/2 of my own. I also have one 2.5"
HDD in a RAID1 that has a tendency to transient errors. It drops
out of the RAID about 2-3 times a year.

Part of the difference is luck (I've not used DeathStars), but it's
mostly a matter of numbers - there are maybe 10 drives in the various
servers in our server room, and my guess is that they are much less used
than the ones in your server setup.

I agree that for well handled disks under good operating
conditions fail rarely, and in line with the manufacturer-stated
reliability. However many desktop systems do not provide
these conditions. And there can be surprises, like the DeathStars
or the exceedingly heat-sensitive Maxtors of some years ago.

Yes, that's another reason why a typical server is more reliable than a
typical desktop machine.

Agreed. And it helps to use version control systems and rotating
or incremental automatic backups to other systems.



Indeed. Wirh a Unix/Linys system, you need to be scared maybe
a year or so. With Windows, you need to be scared half of the time.




I do not agree. RAID1 is cheap, especially as software RAID.

RAID on a server is cheap, and worth the cost. RAID on a desktop is
money wasted (unless you are looking for speed gains), since the same
money could probably be better spent in other ways for greater
reliability.

Well, this is one approach. What I do is have RAID and do copies to
other partitions. Except for Windows, there I just have backup.


One of the reasons I regard Windows as a "toy". Wit Linux/FreeBSD/...
I can just backup/move/restore an application directory and
things will work. No single-point-of-failure monstrosity like
the registry. But there is well-programmed Windows software that
does not need/use the registry. For example, you can copy the World
of Warcraft installation directory to an entirely different machine
and it works there too. Unfortunatrly, not many of the software
defelopers on the MS platform "get it". One of the cultural
disadvantages.


These are a cruel joke IMO!


If it is a Linux software RAID, it will. Otherwise dm-raid may help.
But you absolutely need to test this before you have a problem.

This is definitely one of the big advantages of using Linux software
RAID over any other kind of RAID - recoverability if things go badly wrong.

 

[David Brown]

David Brown wrote

I'm snipping this down to a couple of points (especially since you've
labelled many comments "irrelevant") :

And it isnt even an oxymoron either.

I surrender on this one - I exaggerated (knowingly). I should have
added a smiley, or at least come clean on my last reply - it would have
helped keep the thread informative rather than argumentative.

Any sort of RAID > RAID0, Windows software RAID included, is going to
give /some/ protection against hardware failures. The extent to which
your RAID offers protection depends on your failure recovery strategy.
If the setup is a hardware RAID of the two drives, it's easy. But if
the setup is based on Windows software RAID, then I don't know about
recovery (having never used this setup), and it may be difficult if the
OS disk is trashed.

As a minor point, if the machine in question is physically small then
adding a second disk can raise the temperature of the other disk by
blocking airflow (I've seen that in a tiny server). If you don't
account for this such as by adding extra fans, the higher temperature
will decrease the lifespan of the first disk.

I stand by my claim that adding a second drive to a windows machine and
configuring it as RAID is not the best use of money when your aim is to
protect your data files.

Of course, it's difficult to be accurate and specific without more
details from the OP.


Raid is for uptime, not for backup. To keep your data safe, you need a
good backup solution - uptime is irrelevant. (Maybe the OP wants to
improve his uptime too, but that's not what he asked.)

There are much better ways to do backup than that.

I know - I was just trying to give a quick and easy-to-understand example.

Nope.

If the OP wants to know more about backups, let him ask. A thread
discussing backup strategies could easily get very large and popular.

<reams of you trying to teach your granny to suck eggs flushed where
it belongs>

Without knowing any of the details, I'm guessing that you've got a lot
more experience in this area than I do (IT administration is only a
small part of my job). That means I'll listen with interest to your
advice and suggestions, and try to learn from them, though I may not
agree with everything you say.

 

[Rod Speed]

David Brown wrote

Rod Speed wrote

I'm snipping this down to a couple of points (especially since you've labelled many comments "irrelevant") :

Because they were irrelevant to what was being discussed.

I surrender on this one - I exaggerated (knowingly). I should have added a smiley,

It wasnt a joke.

or at least come clean on my last reply

Whatever that is supposed to mean.

- it would have helped keep the thread informative rather than argumentative.

We'll see...

Any sort of RAID > RAID0, Windows software RAID included, is going to give /some/ protection against hardware
failures.

So your original was just plain wrong.

The extent to which your RAID offers protection depends on your failure recovery strategy.
Nope.

If the setup is a hardware RAID of the two drives, it's easy. But if the setup is based on Windows software RAID,
then I don't know about recovery (having never used this setup), and it may be difficult if the OS disk is trashed.

Wrong again.

As a minor point, if the machine in question is physically small then adding a second disk can raise the temperature
of the other disk by blocking airflow (I've seen that in a tiny server). If you don't account for this such as by
adding extra fans, the higher temperature will decrease the lifespan of the first disk.

That situation is so rare that it isnt worth considering.

I stand by my claim that adding a second drive to a windows machine and configuring it as RAID is not the best use of
money when your aim is to protect your data files.

You dont know that the OP doesnt have appropriate backup.

Of course, it's difficult to be accurate and specific without more details from the OP.

But that didnt stop you making a complete fool of yourself.

Raid is for uptime, not for backup.

Thats just plain wrong too.

To keep your data safe, you need a good backup solution - uptime is irrelevant.

You dont know that the OP doesnt have appropriate backup.

(Maybe the OP wants to improve his uptime too, but that's not what he asked.)

You dont know that the OP doesnt have appropriate backup.

I know - I was just trying to give a quick and easy-to-understand example.

Never could bullshit its way out of a wet paper bag.

If the OP wants to know more about backups, let him ask.

You dont know that the OP doesnt have appropriate backup.

A thread discussing backup strategies could easily get very large and popular.

Not in this group it wont.

Without knowing any of the details, I'm guessing that you've got a lot more experience in this area than I do (IT
administration is only a small part of my job).

You did get that right.

 

[David Brown]

David Brown wrote

Nope.

The benefits of *any* redundancy system are totally dependent on what
happens when part of it fails. If you are are not interesting in
recovering when something has gone wrong, you might as well backup to
write-only media.

Wrong again.

What part of that paragraph was "wrong"? Am I wrong in thinking that
recovering your data from a hardware RAID with a failed drive is easy?
Or am I wrong in saying I don't know about failure recovery with Windows
software raid?

I think you're a little over-keen on telling me everything I say is
wrong, and not too hot on the details. What I am supposed to take away
from a comment like that? If you are trying to inform me that Windows
software raid is actually a useful and worthwhile technique, you're
doing a bad job of it. If it's just a matter of not caring what I or
anyone else learns here, but you are trying to make me challenge my
assumptions, then I guess the response is fair enough.

That situation is so rare that it isnt worth considering.

It's realistic enough that I've seen it - the drive temperature was over
45 C while idle, and I expect under heavy use it could easily get to
temperatures that are lowering the lifespan. You don't get this tiny
servers and NAS systems in professional server setups with controlled
environments, but you *do* get them in small networks at home or at
small businesses.

You dont know that the OP doesnt have appropriate backup.

No, I don't know what backup system he has now or has planned to use.
But his original post looked very much like he thought RAID would give
him data security for his files. And as we all know, RAID is not for
backup.

But that didnt stop you making a complete fool of yourself.



Thats just plain wrong too.

I'm not sure you'll find many others that agree with you here. Do you
care to give a reference or example showing how a RAID setup can satisfy
the requirements of a good backup system?

 

[Rod Speed]

David Brown wrote

Rod Speed wrote

The benefits of *any* redundancy system are totally dependent on what happens when part of it fails.

Wrong. Mirroring is a useful protection against hard drive
failure regardless of what what happens when part of it fails.

If you are are not interesting in recovering when something has gone wrong,

Obviously the OP is.

you might as well backup to write-only media.

Having fun thrashing that straw man ?

What part of that paragraph was "wrong"?

The last half of the last sentence.

Am I wrong in thinking that recovering your data from a hardware RAID with a failed drive is easy?
No.

Or am I wrong in saying I don't know about failure recovery with Windows software raid?

You are wrong about when the OS disk is trashed.

I think you're a little over-keen on telling me everything I say is wrong,

You're lying now. I never ever said that proper backup isnt worth having.

and not too hot on the details. What I am supposed to take away from a comment like that?

That you are just plain wrong on that second half of the last sentence.

If you are trying to inform me that Windows software raid is actually a useful and worthwhile technique,

I didnt even comment on that.

you're doing a bad job of it. If it's just a matter of not caring what I or anyone else learns here,

I wouldnt bother to comment if that was the case.

but you are trying to make me challenge my assumptions,

Nope. I am pointing out where you are just plain wrong.

then I guess the response is fair enough.

It's realistic enough that I've seen it

I didnt say it doesnt ever happen. Rare means that it does happen, rarely.

- the drive temperature was over 45 C while idle, and I expect under heavy use it could easily get to temperatures
that are lowering the lifespan.

Its no news that mounting drives adjacent in a system with
inadequate airflow can see higher than desirable drive temps.

You don't get this tiny servers and NAS systems in professional server setups with controlled environments, but you
*do* get them in small networks at home or at small businesses.

Hardly anyone bothers with TINY servers.

No, I don't know what backup system he has now or has planned to use.
But his original post looked very much like he thought RAID would give
him data security for his files. And as we all know, RAID is not for backup.

It does however give useful extra protection against hard drive
failure which can be handy when the drive fails between backups.

I'm not sure you'll find many others that agree with you here.

More have agreed with me on that than have agreed with your claim.

Do you care to give a reference or example showing how a RAID setup can satisfy the requirements of a good backup
system?

Thats an entirely different matter to your original 'does not noticeably improve data security'

Of course it mirroring improves data security, most obviously
with the new data that has showed up between backups.

 

[Arno]

The benefits of *any* redundancy system are totally dependent on what
happens when part of it fails. If you are are not interesting in
recovering when something has gone wrong, you might as well backup to
write-only media.

From what I hear, there is a significant number of people doing that,
i.e. backup without ever having testet whether they can restore.

[...]

It's realistic enough that I've seen it - the drive temperature was over
45 C while idle, and I expect under heavy use it could easily get to
temperatures that are lowering the lifespan. You don't get this tiny
servers and NAS systems in professional server setups with controlled
environments, but you *do* get them in small networks at home or at
small businesses.

I agree. Thermal design is tricky and temperature monitoring is
important. And a second disk can add significant thermal load.

I'm not sure you'll find many others that agree with you here. Do you
care to give a reference or example showing how a RAID setup can satisfy
the requirements of a good backup system?

Raid serves some of the functions of a full backup, but not all.
Hence it is often called a measure to reduce downtime, implying you
still need a backup. Fact is that there is a set of risks to an
installation and data on disks and that RAID reduces a proper subset
of the ones a backup reduces and that major risks coverd by a backup
are not coverd by RAID. However, from a risk-reduction point of view,
using RAID can be enough to drive the risk of data loss low enough,
for example when you can reinstall and the changed data is of limited
value. RAID has also the advantage that it is far simpler and
generally cheaper than backup.

However, unless you understand the situation, remembering
that "RAID is not backup" is reasonable, if only partially
accurate.

Arno

 

[David Brown]

Where you get to define "good"?

I don't get to define what other people call a "good" backup system, but
I can give a list of things that *I* think are important. And if I've
missed something important, or included something unnecessary, please
correct me.

The requirements of a "good" backup system are:

* Fast and reliable recovery of data, including parts of the data.
* Recovery of data recently stored, so that not too much is lost on a
failure.
* Recovery of data over a range of time frames (e.g., restoring a file
that was deleted a few weeks ago).
* Protection against hardware failures of the source server and backup
servers.
* Protection against file system or file corruption on servers.
* Protection against user error (deleting or overwriting files).
* Protection against the effects of malware or attacks.
* Protection against fire and theft.
* Security and access control must be matched to the requirements of the
data.

This means your backup system must be:

* Straightforward, testable and /tested/ recovery procedure.
* Recoverable even after total failure (such as the death of the machine
that normally runs backups and restores).
* Preferably automatic with no manual intervention. If manual
intervention is needed, there should be clear procedures (signing out
tapes, whatever).
* Reporting of the success or failure of the backups, and someone
checking these reports.
* Regular "snapshots", with varying lifetimes (i.e., daily snapshots
kept for a couple of weeks, weekly snapshots for a couple of months, etc.)
* Off-site backups or copies of the backups.
* Controlled security and appropriate access to the backups.

It works for backup. It protects against some things. It helps.
This cannot be denied. End of story.

A mirror raid helps against hardware failure of one of the drives - that
can't be denied. As Rod pointed out, this is particularly relevant for
files that haven't yet been copied by the backup procedure. And
therefore, it /does/ help. Even with a wonderful backup system, it
makes sense to have raid on the file server - it's part of an overall
reliable file server solution. But raid mirror in itself is so far from
fulfilling the requirements I gave above for a good backup system, that
I cannot see why anyone would call raid a backup solution.

 

[David Brown]

David Brown wrote


Wrong. Mirroring is a useful protection against hard drive failure
regardless of what what happens when part of it fails.

Consider a setup like this:

Disk A, 750G:
partition 1, 250G
partition 2, 500G
Disk B, 500G:
partition 1, 500G

You put your OS, programs, etc., on "C drive" on partition A.1. You
mirror partition A.2 and B.1, and put your data on this "D drive".

Disk A dies.

You have a safe copy of all your data on the mirror B.1. But your OS
drive is dead.

How do you get your data off B.1 again?

If you want to tell me it's easy, that's fine - as I've said before, I
know about software raid on Linux but not on Windows. If it's easy,
then you have a good system because you can easily recover your data
after a failure.

If you want to tell me it's a stupid setup because you can't continue
working, and the "C" drive should also be on the mirror, then that's
also fine. You'd then be saying that it's a bad idea because recovery
is hard.

If it is hard to recover data here, then you can certainly argue that it
is still better than nothing - hard but not impossible. But the
benefits of the protection are much smaller if recovery is difficult,
since you want to get your data back in a safe and timely manner.

Obviously the OP is.


Having fun thrashing that straw man ?

There are a *lot* of people who effectively backup to write-only media -
I'm sure you've met plenty who think they have a good backup system
until the day comes when they need to do a restore. But fair enough,
it's a straw man here.

The last half of the last sentence.

So it's not difficult to recover after failure using Windows software
raid? Does that apply when the whole disk (OS and data) are installed
on a software raid? And does it apply when you have just the data on
the software raid?

Remember, I had originally made a suggestion of just using 500 GB of the
750 GB for raid for storing data (see the details earlier in this post).
I know it's straightforward to access this data on a Linux system even
if drive with the OS has failed - you can boot a live CD, and mount it
directly. So for Linux, it's a perfectly reasonable setup with a
different balance between efficient use of disk space and redundancy and
uptime than you would get with a full drive raid.

But I'd like to be absolutely clear on this one - is it equally simple
with Windows software raid, or was it such a stupid idea for windows
that you didn't realize I'd suggested it for consideration? I don't
have the experience with windows software raid to know here - instinct
tells me it's a stupid idea (hence my original sarcastic post), but I
could be wrong.

It does however give useful extra protection against hard drive
failure which can be handy when the drive fails between backups.

This point is certainly true, and one that I hadn't taken into account -
I was thinking only of longer term data security.

Thats an entirely different matter to your original 'does not
noticeably improve data security'

Fair enough.

I think we have a slightly different idea of what the risks are
regarding data - we have different backgrounds, different experiences,
and different types of hardware, software, users, and data use. For my
users, I don't expect to see any noticeable data loss if a desktop
harddrive dies. It means lost productivity, and an inconvenience, but
not data loss other than perhaps files that are open at the time.

For home users without a server (with backup), I firmly believe that
using raid mirroring is of very little benefit compared to spending the
same money on a backup system (for home users, that typically means DVD
writers, or perhaps an Internet-based backup system), or simply a second
drive to which you make regular copies.

Either way, I don't think desktop raid is a big gain for data security.
But clearly it does provide *some* gain - and if you already have a
good backup system, then it adds a little more (as well as speed and
uptime benefits).

 

[David Brown]

I've never lost files due to malware, etc, IF those files were kept
off the system partition, for example on D:. In fact I always have a
D: partition to back things up on, because it makes it so easy to
restore things after a drive C: wipe-and-reinstall of Windows.

Obviously, periodic backups off the harddrive are highly recommended,
as well.

Nor have /I/ lost files due to malware, and the only time I lost files
due to file system corruption was on an old Win95 machine. But I know
others who /have/ lost data, and I've helped recover data for other
people (the typical situation is that the machine won't boot windows due
to either malware, registry corruption, or some "security" software
which decides windows itself is malware).

I agree fully about having a second partition for data.

 

[Rod Speed]

David Brown wrote

chrisv wrote

Nor have /I/ lost files due to malware, and the only time I lost files due to file system corruption was on an old
Win95 machine.

I didnt lose anything with any of those either.

But I know others who /have/ lost data,

Yes, plenty of fools dont bother with adequate back of what they care about losing.

and I've helped recover data for other people (the typical situation is that the machine won't boot windows due to
either malware, registry corruption, or some "security" software which decides windows itself is malware).

Yes, plenty of fools dont bother with adequate back of what they care about losing.

I agree fully about having a second partition for data.

I dont. Its perfectly possible to have adequate backup of what matters without that.

 

[Rod Speed]

David Brown wrote

Rod Speed wrote

Consider a setup like this:

Disk A, 750G:
partition 1, 250G
partition 2, 500G
Disk B, 500G:
partition 1, 500G

You put your OS, programs, etc., on "C drive" on partition A.1. You mirror partition A.2 and B.1, and put your data
on this "D drive".

Disk A dies.

You have a safe copy of all your data on the mirror B.1. But your OS drive is dead.

How do you get your data off B.1 again?

You reinstall the OS on the replacement drive and carry on
regardless. Not a shred of rocket science whatever required.

If you want to tell me it's easy,

Corse its completely trivial.

that's fine - as I've said before, I know about software raid on Linux but not on Windows. If it's easy, then you
have a good system because you can easily recover your data after a failure.

And that is precisely what you have.

If you want to tell me it's a stupid setup
Nope.

because you can't continue working, and the "C" drive should also be on the mirror, then that's also fine. You'd then
be saying that it's a bad idea because recovery is hard.

Recovery is completely trivial.

If it is hard to recover data here,

It isnt.

then you can certainly argue that it is still better than nothing - hard but not impossible.

It isnt that either.

But the benefits of the protection are much smaller if recovery is difficult,

It isnt.

since you want to get your data back in a safe and timely manner.

Its completely trivial to do that.

And the recovery is completely obviously to anyone with even half a clue too.

There are a *lot* of people who effectively backup to write-only media

There arent really that many anymore. Essentially because
write only media is so slow and of such limited capacity.

- I'm sure you've met plenty who think they have a good backup
system until the day comes when they need to do a restore.

Sure, but thats rather less common now.

But fair enough, it's a straw man here.

It is indeed.

So it's not difficult to recover after failure using Windows software raid?

Completely trivial in fact.

Does that apply when the whole disk (OS and data) are installed on a software raid?
Yes.

And does it apply when you have just the data on the software raid?
Yes.

Remember, I had originally made a suggestion of just using 500 GB of the 750 GB for raid for storing data (see the
details earlier in this post). I know it's straightforward to access this data on a Linux system even if drive with
the OS has failed - you can boot a live CD, and mount it directly.

You can with Win too.

So for Linux, it's a perfectly reasonable setup with a different balance between efficient use of disk space and
redundancy and uptime than you would get with a full drive raid.

But I'd like to be absolutely clear on this one - is it equally simple with Windows software raid,

Yes. And you can use a Linux live CD to do that too with Win.

or was it such a stupid idea for windows that you didn't realize I'd suggested it for consideration?
Nope.

I don't have the experience with windows software raid to know here - instinct
tells me it's a stupid idea (hence my original sarcastic post), but I could be wrong.

You are indeed. You can in fact use either a Linux
live CD or a Win equivalent, whichever you prefer.

This point is certainly true, and one that I hadn't taken into
account - I was thinking only of longer term data security.

Fair enough.

I think we have a slightly different idea of what the risks are regarding data
Nope.

- we have different backgrounds, different experiences,
Yes.

and different types of hardware, software, users, and data use.
Nope.

For my users, I don't expect to see any noticeable data loss if a desktop
harddrive dies. It means lost productivity, and an inconvenience, but
not data loss other than perhaps files that are open at the time.

For home users without a server (with backup), I firmly believe that using raid mirroring is of very little benefit
compared to spending the same money on a backup system

They arent alternatives.

(for home users, that typically means DVD writers, or perhaps an Internet-based backup system),

Nope. Most use external hard drives now.

or simply a second drive to which you make regular copies.

Anyone with a clue uses and external hard drive to
reduce the risk of fire or theft etc affecting both drives.

Either way, I don't think desktop raid is a big gain for data security.

Only in the sense that hard drive failure is uncommon.

But clearly it does provide *some* gain - and if you already have a good backup system, then it adds a little more (as
well as speed and uptime benefits).

Thats just plain wrong with home systems.

The big advantage of mirroring when you already have
decent backup is that it provides a useful extra level of
protection against hardware failure between backup runs.

 

[Rod Speed]

David Brown wrote

chrisv wrote

I don't get to define what other people call a "good" backup system,
but I can give a list of things that *I* think are important. And if I've missed something important, or included
something unnecessary,

Or got something wrong.

please correct me.

The requirements of a "good" backup system are:

* Fast and reliable recovery of data, including parts of the data.

Doesnt need to be fast with home systems given that failure is so uncommon.

* Recovery of data recently stored, so that not too much is lost on a failure.

That varys with how the system is used. If the user has enough of a clue
to save new work like photos etc to more than one place, the backup
system doesnt really need to worry too much about this sort of thing.

* Recovery of data over a range of time frames (e.g., restoring a file that was deleted a few weeks ago).

Its very arguable if home systems really need this, particularly
if the irreplaceable stuff like photos etc are manually written to
more than one place when they enter the system.

* Protection against hardware failures of the source server and backup servers.

Not relevant to most of the home systems being discussed.

* Protection against file system or file corruption on servers.

Not relevant to most of the home systems being discussed.

* Protection against user error (deleting or overwriting files).

Again, that depends on what the user does with the irreplaceable stuff.

* Protection against the effects of malware or attacks.

Even that varys with how vulnerable the system is to that sort of thing.

* Protection against fire and theft.

An important distinction needs to be made between irreplaceable
data and stuff that can be replaced with some effort. If the house
has burnt down, it doesnt really matter if some time has to be
spend getting stuff again when it is replaceable.

* Security and access control must be matched to the requirements of the data.

Waffle with home systems being discussed.

This means your backup system must be:

* Straightforward, testable and /tested/ recovery procedure.

Overkill with most home systems.

* Recoverable even after total failure (such as the death of the machine that normally runs backups and restores).

What matters with the home systems is the irreplaceable data.

* Preferably automatic with no manual intervention.

Waste of money with the home systems being discussed.

If manual intervention is needed, there should be clear procedures (signing out tapes, whatever).

Overkill with the home systems being discussed.

* Reporting of the success or failure of the backups, and someone checking these reports.

Gross overkill with the home systems being discussed.

* Regular "snapshots", with varying lifetimes (i.e., daily snapshots kept for a couple of weeks, weekly snapshots for
a couple of months, etc.)

Gross overkill with the home systems being discussed.

* Off-site backups or copies of the backups.

Only necessary with the irreplaceable data with the home systems being discussed.

* Controlled security and appropriate access to the backups.

Gross overkill with the home systems being discussed.

A mirror raid helps against hardware failure of one of the drives -
that can't be denied. As Rod pointed out, this is particularly
relevant for files that haven't yet been copied by the backup
procedure. And therefore, it /does/ help. Even with a wonderful
backup system, it makes sense to have raid on the file server - it's part of an overall reliable file server solution.
But raid mirror in itself is so far from fulfilling the requirements I gave above for a good backup system, that I
cannot see why anyone would call raid a backup solution.

No one did. What was being discussed was your silly original claim that it adds nothing.

That is just plain wrong.