What is RAID0 good for?


M

M.L.

My friend has a Win XP PowerSpec B647 desktop with two 250 GB hard
drives configured in the BIOS as RAID0. It appears that whatever
happens to one drive happens to the other, so when she was infected
with a virus both hard drives were infected, and both were
simultaneously cleaned by the same antivirus scanner.

What good is having those 2 drives perform like that when she is a
non-techie home user who would be better off with the use of 2
independent hard drives? Is there a way to turn off the RAID behavior
so she can get usage more suitable to her needs? Thanks.
 
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M

mscotgrove

My friend has a Win XP  PowerSpec B647 desktop with two 250 GB hard
drives configured in the BIOS as RAID0. It appears that whatever
happens to one drive happens to the other, so when she was infected
with a virus both hard drives were infected, and both were
simultaneously cleaned by the same antivirus scanner.

What good is having those 2 drives perform like that when she is a
non-techie home user who would be better off with the use of 2
independent hard drives? Is there a way to turn off the RAID behavior
so she can get usage more suitable to her needs? Thanks.
RAID 0 is nor really RAID as there is no redundancy. As discovered,
if one drive fails, in effect all data is lost.

The reason for it, in theory it will make the drive run faster. For
the average user, this speed difference may never be seen.

A safer option would be to use JBOD (Just a Bunch Of Disks) and
concatinate the two to make a single 500GB drive.

If a 500GB drive was not required, then 2 x 250GB drives would be a
nice simple solution. This is the option I would choose.

To protect against single disk failure, you require RAID 1. However a
virus problem would still ingect both drives.

To change the setup will require reformating both drives, and so all
current data MUST be backed up first, and then the operating system
etc will need reloading. Probably not worth the effort, just make
sure you have regular backups.

Michael
www.cnwrecover.com
 
A

Arno

M.L. said:
My friend has a Win XP PowerSpec B647 desktop with two 250 GB hard
drives configured in the BIOS as RAID0. It appears that whatever
happens to one drive happens to the other, so when she was infected
with a virus both hard drives were infected, and both were
simultaneously cleaned by the same antivirus scanner.
What good is having those 2 drives perform like that when she is a
non-techie home user who would be better off with the use of 2
independent hard drives? Is there a way to turn off the RAID behavior
so she can get usage more suitable to her needs? Thanks.
RAID does not help against Malware at all. That is not
its purpose. Incidentially RAID-zero has zero RAID
functionality and does indcreae the risk of data-loss, while
it gives some speed improvement.

No, there is not much sense in this configuration for your friend.

Arno
 
G

GMAN

RAID 0 is nor really RAID as there is no redundancy. As discovered,
if one drive fails, in effect all data is lost.

The reason for it, in theory it will make the drive run faster. For
the average user, this speed difference may never be seen.

A safer option would be to use JBOD (Just a Bunch Of Disks) and
concatinate the two to make a single 500GB drive.
How is JBOD "safer" than Raid0 ?
 
A

Arno

How is JBOD "safer" than Raid0 ?
It is, but only by a tiny bit and only with the right
filesystem. The thing is that with RAID0, all data is lost
on a disk failure. With concatenated disks, you may recover
data from the non-failed disk.

Both options are strictly for temporary, low-reliability
storage. Don't use them to hold production data that is
not replicated in other places.

Arno
 
D

David Brown

It is, but only by a tiny bit and only with the right
filesystem. The thing is that with RAID0, all data is lost
on a disk failure. With concatenated disks, you may recover
data from the non-failed disk.
"JBOD" has two meanings - it can mean "spanning" or "concatenation",
which is what you mean here, or it can mean "treat as several
independent disks".

For spanned disk sets, you have little improvement in safety over Raid0
- files are often scattered around so that you will often have parts on
each disk, and metadata in particular is often spread over the disk
(unless the disk space is very underused - in which case a single disk
is a better choice). In particular, if the first disk is lost then you
will practically speaking lose everything.

Treating the two disks entirely independently is a lot safer, especially
if you copy data across the two disks regularly. So that sort of "JBOD"
is much better than Raid0 (and much safer than Raid1 for typical home
usage).
Both options are strictly for temporary, low-reliability
storage. Don't use them to hold production data that is
not replicated in other places.
Raid is not about data safety - it's about uptime/downtime, and the
convenience of not having to restore from backup when a disk dies. It
doesn't replace backups and data replication.
 
D

David Brown

My friend has a Win XP PowerSpec B647 desktop with two 250 GB hard
drives configured in the BIOS as RAID0. It appears that whatever
happens to one drive happens to the other, so when she was infected
with a virus both hard drives were infected, and both were
simultaneously cleaned by the same antivirus scanner.

What good is having those 2 drives perform like that when she is a
non-techie home user who would be better off with the use of 2
independent hard drives? Is there a way to turn off the RAID behavior
so she can get usage more suitable to her needs? Thanks.
Raid0 stripes the two drives for speed and increased capacity, it does
not make any copies.

Raid1 mirrors the drives, so that each holds an exact copy of the other.
This is mainly so that if one of the drives dies, everything carries
on the same. It can also make reads a bit faster, but writes a bit slower.


Redundant raid (raid1 or higher) offer no protection against the likely
causes of problems on a home machine - they only protect against hard
drive failure. While hard drives do occasionally die, the biggest
threats the typical home users' data faces are malware, user error, and
file system corruption. A Raid1 mirror will faithfully replicate all
these faults across the two drives.


So what your friend really needs is a drive for using, and a decent
backup of their data. Given that hardware, the easiest system is to use
one disk as the main disk, and the other as an independent disk for
backups. Keep copies of everything important on both disks, and you
will have a reasonably safe system. It won't protect against the most
vicious of malware that scans the whole system for files to destroy, or
the most stupid of user errors, or the most unlucky of failures (combine
it with copying to CD/DVDs). But it will be a big step forward.
 
A

Arno

"JBOD" has two meanings - it can mean "spanning" or "concatenation",
which is what you mean here, or it can mean "treat as several
independent disks".
Actually it typically means either "spanning" or "independent disks
in one storage device". It makes absolutely no sense to call some
independent disks a "JBOD". Not that people have been using that
term for a lot of things. It actually has no defined meaning at all.
For spanned disk sets, you have little improvement in safety over Raid0
- files are often scattered around so that you will often have parts on
each disk, and metadata in particular is often spread over the disk
(unless the disk space is very underused - in which case a single disk
is a better choice). In particular, if the first disk is lost then you
will practically speaking lose everything.
That is why I said "very little", as in "insignificant".
Treating the two disks entirely independently is a lot safer, especially
if you copy data across the two disks regularly. So that sort of "JBOD"
is much better than Raid0 (and much safer than Raid1 for typical home
usage).
Raid is not about data safety - it's about uptime/downtime, and the
convenience of not having to restore from backup when a disk dies. It
doesn't replace backups and data replication.
I don't agree. RAID (nonzero) does replace replication, it does not
replace backup. It happens to be about data safety, it just
gives you a worse coverage than a backup, so you typically still
need a backup in addition. But if you, for example, do not need
a backup but can do a new installation with fixed, well known
effort, RAID is one way to bring teh failure probability down
enough that a backup becomes cost-ineffective.

Arno
 
A

Arno

Raid0 stripes the two drives for speed and increased capacity, it does
not make any copies.
Raid1 mirrors the drives, so that each holds an exact copy of the other.
This is mainly so that if one of the drives dies, everything carries
on the same. It can also make reads a bit faster, but writes a bit slower.

Redundant raid (raid1 or higher) offer no protection against the likely
causes of problems on a home machine - they only protect against hard
drive failure. While hard drives do occasionally die, the biggest
threats the typical home users' data faces are malware, user error, and
file system corruption. A Raid1 mirror will faithfully replicate all
these faults across the two drives.
Indeed. The important thing is to remember that (redundant) RAID
is not backup. If your situation requires a backup (and most do),
then RAID is not a replacement for it.
So what your friend really needs is a drive for using, and a decent
backup of their data. Given that hardware, the easiest system is to use
one disk as the main disk, and the other as an independent disk for
backups. Keep copies of everything important on both disks, and you
will have a reasonably safe system. It won't protect against the most
vicious of malware that scans the whole system for files to destroy, or
the most stupid of user errors, or the most unlucky of failures (combine
it with copying to CD/DVDs). But it will be a big step forward.
Incidentially, common sysadmin wisdom says that anything you do not
want to lose you should have in 3 copies (master, backup1 and backup2)
and better 4 copies, as operator error may well destroy one additional
copy during manual backup or restore. So a real backup should use
3 rotating media sets.

But one independent copy is already massively better than nothing.

Arno
 
M

Man-wai Chang

What good is having those 2 drives perform like that when she is a
non-techie home user who would be better off with the use of 2
independent hard drives? Is there a way to turn off the RAID behavior
so she can get usage more suitable to her needs? Thanks.
Nothing could replace a good backup!!

--
@~@ Might, Courage, Vision, SINCERITY.
/ v \ Simplicity is Beauty! May the Force and Farce be with you!
/( _ )\ (x86_64 Ubuntu 9.10) Linux 2.6.35.2
^ ^ 22:30:01 up 42 min 0 users load average: 1.34 1.23 1.10
ä¸å€Ÿè²¸! ä¸è©é¨™! ä¸æ´äº¤! ä¸æ‰“交! ä¸æ‰“劫! ä¸è‡ªæ®º! è«‹è€ƒæ…®ç¶œæ´ (CSSA):
http://www.swd.gov.hk/tc/index/site_pubsvc/page_socsecu/sub_addressesa
 
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D

David Brown

Actually it typically means either "spanning" or "independent disks
in one storage device". It makes absolutely no sense to call some
independent disks a "JBOD". Not that people have been using that
term for a lot of things. It actually has no defined meaning at all.
I don't claim Wikipedia to be the "definition", but it does show the usage:

<http://en.wikipedia.org/wiki/JBOD#JBOD>

I think "independent disks in one storage device" and "independent
disks" really mean the same thing - each disk is treated by itself.
Anyway, it's not worth arguing about - we both know what I mean, and we
agree there is no fixed definition of the term.

That is why I said "very little", as in "insignificant".
Fair enough.
I don't agree. RAID (nonzero) does replace replication, it does not
replace backup. It happens to be about data safety, it just
gives you a worse coverage than a backup, so you typically still
need a backup in addition. But if you, for example, do not need
a backup but can do a new installation with fixed, well known
effort, RAID is one way to bring teh failure probability down
enough that a backup becomes cost-ineffective.
If you can get everything back from a re-installation, then your
installation source is your backup.

RAID gives you redundancy on the hard disk hardware - that's all. It
reduces the risk of losing time or data due to a hardware failure, but
does nothing towards reducing the risk from other conditions (malware,
user error, or file system corruption). You can argue the benefits of
"replication", "backup" and "data safety" as much as you want but in
reality it comes down to what can go wrong, the chances of that
happening, and the consequences of such failures. Raid covers a certain
class of failure (hard drive failure) which is typically fairly low
risk, and reduces the consequences to almost nothing. That's definitely
nice.

But since raid does not cover the other sources of failure that are
generally more common, it is at best a small part of a data safety
solution. And something that /does/ cover such failures - a good backup
solution - also covers hard drive failure. So the backup is your data
safety solution. Raid enhances that by reducing the consequences of
certain failures (no lost uptime, and no loses of data that has not yet
been backed up). But it is nothing more than a little add-on to a
backup solution, and certainly a waste for home usage like the O/P's.
 
D

David Brown

Indeed. The important thing is to remember that (redundant) RAID
is not backup. If your situation requires a backup (and most do),
then RAID is not a replacement for it.


Incidentially, common sysadmin wisdom says that anything you do not
want to lose you should have in 3 copies (master, backup1 and backup2)
and better 4 copies, as operator error may well destroy one additional
copy during manual backup or restore. So a real backup should use
3 rotating media sets.
Yes, with backups it's "the more the merrier" - at least, as long as you
keep track of them and don't mix up older and newer backups (as can
easily happen with ad-hoc backups).

It is also important to keep your backups (or one copy at least)
off-site. Nothing is more annoying than when the burglar takes your PC
and your backup CDs...
 
A

Arno

I don't claim Wikipedia to be the "definition", but it does show the usage:

I think "independent disks in one storage device" and "independent
disks" really mean the same thing - each disk is treated by itself.
Anyway, it's not worth arguing about - we both know what I mean, and we
agree there is no fixed definition of the term.
I can agree to that ;-)

Fair enough.
If you can get everything back from a re-installation, then your
installation source is your backup.
Hmm. Ok, that _is_ a legitimate view.
RAID gives you redundancy on the hard disk hardware - that's all. It
reduces the risk of losing time or data due to a hardware failure, but
does nothing towards reducing the risk from other conditions (malware,
user error, or file system corruption). You can argue the benefits of
"replication", "backup" and "data safety" as much as you want but in
reality it comes down to what can go wrong, the chances of that
happening, and the consequences of such failures. Raid covers a certain
class of failure (hard drive failure) which is typically fairly low
risk, and reduces the consequences to almost nothing. That's definitely
nice.
Well, the risk of disk failure has certainly gone down. I lost
several disks and went to RAID some years ago. Of course none
of my disks has failed permanently since.

Incidentially, RAID also covers things that Backup does not, namely
non-permanent disk failure and uptime improvement.

Concrete example: I have a low-power fileserver/firewall/email-
server with 3-way RAID1 on notebook disks. Every few months,
one of the notebook disks has a problem and becomes inacessible.
Without the RAID, the server would crash. With it, it stays up,
and I pull and replug the disk when I have time. These failures
so far were all non-permanent, nothing in the SMART log, no data
corruption, nothing.

But since raid does not cover the other sources of failure that are
generally more common, it is at best a small part of a data safety
solution. And something that /does/ cover such failures - a good backup
solution - also covers hard drive failure. So the backup is your data
safety solution. Raid enhances that by reducing the consequences of
certain failures (no lost uptime, and no loses of data that has not yet
been backed up). But it is nothing more than a little add-on to a
backup solution, and certainly a waste for home usage like the O/P's.
Lets just say that RAID and backup cover mostly different problems.
In practically all cases "RAID is not backup!" does cover it and
what people usually need is backup.

However for some things, it is ceratinly important and there
"Backup is not RAID!" is even more true.

Arno
 
D

DevilsPGD

In message <4c6951cc$0$32127$8404b019@news.wineasy.se> David Brown
I think "independent disks in one storage device" and "independent
disks" really mean the same thing - each disk is treated by itself.
Anyway, it's not worth arguing about - we both know what I mean, and we
agree there is no fixed definition of the term.
More important, some controllers do concatenate drives in JBOD mode,
some do not, so regardless of the "actual" definition, both are used in
practice.
 
D

David Brown

Hmm. Ok, that _is_ a legitimate view.


Well, the risk of disk failure has certainly gone down. I lost
several disks and went to RAID some years ago. Of course none
of my disks has failed permanently since.

Incidentially, RAID also covers things that Backup does not, namely
non-permanent disk failure and uptime improvement.
"Non-permanent disk failure" is a bit doubtful - if a disk is having
enough trouble that it can't be handled with its own ECC and extra
sectors, then it should probably be considered as failed.

And raid certainly covers other things that backup does not - uptime is
one thing, others are increased speed and capacity.
Concrete example: I have a low-power fileserver/firewall/email-
server with 3-way RAID1 on notebook disks. Every few months,
one of the notebook disks has a problem and becomes inacessible.
Without the RAID, the server would crash. With it, it stays up,
and I pull and replug the disk when I have time. These failures
so far were all non-permanent, nothing in the SMART log, no data
corruption, nothing.
Raid certainly gives you greater uptime here, but I would want to find
out and fix the underlying problem!
Lets just say that RAID and backup cover mostly different problems.
In practically all cases "RAID is not backup!" does cover it and
what people usually need is backup.

However for some things, it is ceratinly important and there
"Backup is not RAID!" is even more true.
Agreed - they are both useful and complementary.
 
A

Arno

"Non-permanent disk failure" is a bit doubtful - if a disk is having
enough trouble that it can't be handled with its own ECC and extra
sectors, then it should probably be considered as failed.
Actually I had about 5 of these on different notebook disks
attached to different controllers running 24/7. These are not
surface errors or the like, the interface just goes down and
the disks stops to respond. Power-cyle it and everything is
fine again.
And raid certainly covers other things that backup does not - uptime is
one thing, others are increased speed and capacity.
Raid certainly gives you greater uptime here, but I would want to find
out and fix the underlying problem!
The underlying problem seems to be firmaware issues with notebook
disks when running them 24/7 for years. I don't think there is a
fix besides going to 3.5" drives, which is not an option here due
to power consumption. As this happens roughly once every 3 years
per disk, I can life with it.

Arno
 
G

GMAN

How is JBOD "safer" than Raid0 ?
It is, but only by a tiny bit and only with the right
filesystem. The thing is that with RAID0, all data is lost
on a disk failure. With concatenated disks, you may recover
data from the non-failed disk.

Both options are strictly for temporary, low-reliability
storage. Don't use them to hold production data that is
not replicated in other places.

Arno[/QUOTE]
Thanks for the explanation.
 
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P

Peter Knutsen

RAID 0 is nor really RAID as there is no redundancy. As discovered,
if one drive fails, in effect all data is lost.

The reason for it, in theory it will make the drive run faster. For
the average user, this speed difference may never be seen.

A safer option would be to use JBOD (Just a Bunch Of Disks) and
concatinate the two to make a single 500GB drive.

If a 500GB drive was not required, then 2 x 250GB drives would be a
nice simple solution. This is the option I would choose.
I have two hard drives in my current desktop, and have the Windows XP
swapfile on the second drive, which is supposed to be faster.
To protect against single disk failure, you require RAID 1. However a
virus problem would still ingect both drives.
RAID1 is also twice as expensive. You buy two 250 GB hard drives, but
they function as one 250 GB hard drive. The risk if data loss is greatly
reduced, however.
To change the setup will require reformating both drives, and so all
current data MUST be backed up first, and then the operating system
etc will need reloading. Probably not worth the effort, just make
sure you have regular backups.
If it was me, I'd be happy with the extra disc speed of RAID0 (provided
there is any), but I'd be on the lookout for some kind of third hard
drive, small in size, for important data such as email (I backup my own
creative efforts using DropBox, but I don't like the idea of putting my
email there too. That's too private to share with the cloud).

I think my ideal computer, if money wasn't a problem (which, sadly, they
are), would be an SSD for booting up, and installing frequently used
programes and games (40 GB should be plenty), then a couple of large and
very quiet hard drives, no problem if they're slow, for storing files
and installing most games, and finally then one more set of hard drives,
very small, in RAID1, for my important files. 10 GB should be more than
enough for that. Since they're all small files, access time and transfer
time is totally irrelevant, as long as they're quiet and reliable.

Not sure where I should place the swap file on such a machine. Although
being a dream machine, it should have obscene amounts of RAM anyway.
 
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