Poor raid 1 performance?


M

Mark

Peter said:
http://www.9to5computer.com/atto/Comparing-Raid-Configurations.htm
http://www.storagereview.com/guide2000/ref/hdd/perf/raid/levels/singleLevel1.html

With a good controller, sequential read performance equals that of a single
drive, random read performance scales up with number of drives in a RAID.

Thanks. These were the sorts of descriptions that led me to hope that
raid 1 would lead to improved read performance. Eg, one site says that
"Read performance is faster than a single disk; (if the array controller
is capable of performing simultaneous reads from both devices of a
mirrored pair)."

This is why I was then suspecting that the motherboard implementations
are poor. On the other hand, it might be just that the test was more
reflective of sequential than random read performance.

Can anyone suggest a raid 1 array that has improved performance?
 
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M

Mark

Antoine said:
Yes, but also _any_ read is done twice, on both channels and both mechanisms
(and furthermore they are then checked for equality between, which adds a
step, which could be a reason for misperformance).

I do not see why you could see improvements, any other things being equal of
course.

What am I missing here?


Antoine

As another poster pointed out, it is suggested that raid 1 will improve
performance. It seems to very much depend on how raid 1 is implemented.
For maximum data integrity, you can read the same sector from both
drives and ensure that they do agree.

However, this really isn't a requirement for me. A single drive does
usually return the correct result. I am much more concerned with having
a duplicate drive in case one of the drives crashes. Assuming the drives
are okay (which is the usual case and should be detectable), just
reading from one of the drives is sufficient. Hence, why can't a
mirrored pair be accessed like a striped pair (ie, raid 0) which does
result in increased performance?
 
R

Rod Speed

Gerhard Fiedler said:
Rod Speed wrote
That's why I wrote "critical data".

Critical data aint necessarily volatile data.
I consider the result of my work "critical", as it is what
I get paid for. If it takes me half a day to redo the work
of a day, and I do daily backups (both probably a common
situation for everybody who works with a computer), a
RAID1 array is a quite nifty thing, as it should give me
approximately 0 downtime in case of a disk problem.

The obvious approach is a higher frequency of backup, like hourly.
Otherwise, I could easily have a day downtime (need to get drive,
restore last image, redo all the work that happened afterwards).

That just means you need more than one drive, not that you need RAID.

And if your system gets infected, you may have a
problem that RAID wont do a damned thing about.
The only computer-caused downtime I had so far was
either a harddisk crash or a Windows reinstall :) -- and
RAID1 is supposed to crack down on the first one.
(I haven't had a crash since I installed my arrays...)

And if the failure is in the raid hardware, not the drives,
you may well have much more of a problem than you
would have with duplicated PCs and no RAID at all.
RAID1 is no substitution for backup, of course, it's
an enhancement for an adequate backup strategy.

Not necessarily a very useful enhancement
tho over just duplicating the PC, even if the
spare is the previously replaced system.

Thats much more likely to see you
up much more quickly on any failure.
Most don't, but then most don't create critical data. I'd
recommend it for everybody who creates critical data.

I wouldnt, duplicating much more than just the
hard drive makes a hell of a lot more sense.
 
R

Rod Speed

Mark said:
Rod Speed wrote
My computer hasn't always recovered from hibernation okay, something
to do with the power management. Hence, I am hesitant to use it.

Makes more sense to fix that than to try to find
a RAID that improves the read performance.
Also, I do like the idea of rebooting regularly to stop the system
becoming bloated with memory resident programs that I don't need.

No need with a decent modern OS like XP.
Okay, you obviously don't play games. First, having them stay in the
background quite often reduces the computer to a crawl.

Bullshit with a properly configured system.
Second, even if you are in the game, level loads (and saving and loading your
position) can be very slow.

RAID aint gunna fix that.
I'd be interested in other techniques. What do you suggest?

More physical ram.
 
G

Gerhard Fiedler

Rod said:
I wouldnt, duplicating much more than just the hard drive makes a hell of
a lot more sense.

You definitely have a point here. But the price point is also quite
different.

Gerhard
 
B

Bob Willard

Antoine said:
In Bob Willard wrote:



Yes, but also _any_ read is done twice, on both channels and both mechanisms
(and furthermore they are then checked for equality between, which adds a
step, which could be a reason for misperformance).

I do not see why you could see improvements, any other things being equal of
course.

What am I missing here?


Antoine
It is a designer's choice whether a read is or is not done twice and
compared;
RAID1 does not require that. One alternative is to issue the read to the
least busy HD or to that HD which will have the minimum seek to complete
the read.

Reading from both HDs and then comparing probably adds little data integrity
when compared with simply reading from one HD and counting on the ECC check
to catch a bad read or a bad sector.
 
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R

Rod Speed

Gerhard Fiedler said:
Rod Speed wrote
You definitely have a point here. But
the price point is also quite different.

Not if you use the previous main system as the backup.

And many of us have more than one system for various reasons as well.
 
M

Mark

Rod said:
Makes more sense to fix that than to try to find
a RAID that improves the read performance.




No need with a decent modern OS like XP.




Bullshit with a properly configured system.

Mate, you have no idea. The minimum requirements of some current games
are 512 megabytes of ram, and the preferred configuration is 1 gig! How
many of these do you think you can have loaded at once before the system
is reduced to a crawl? In fact, due to games directly accessing
hardware, there are issues with running more than one game
simultaneously. Hence, you need to quit one game before loading up
another. Alt-tabbing also sometimes doesn't work well due to problems
with display drivers. Again, if you played games, you would know how
tempermental the display drivers can be.

RAID aint gunna fix that.

Why not? Raid can increase read performance, so why would this not lead
to faster load times?
More physical ram.

I am planning on having 2 gigs of ram, which is the most I can afford.
However, how much ram do you have in your system? My system is currently
using about 200 gigs of storage. It is not possible to fill a
motherboard with 200 gigs of ram, so obviously the HD still needs to be
used to load information.
 
R

Rod Speed

Mark said:
Rod Speed wrote
Mate, you have no idea.

We'll see...
The minimum requirements of some current games are 512 megabytes of ram, and
the preferred configuration is 1 gig!
How many of these do you think you can have loaded at once before the system
is reduced to a crawl?

YOU have no idea. It aint the ram use that slows systems
to a crawl, and anyone with a clue can have 4G of ram anyway.
In fact, due to games directly accessing hardware, there are issues with
running more than one game simultaneously.

Then keep those in a ram drive, stupid.
Hence, you need to quit one game before loading up another. Alt-tabbing also
sometimes doesn't work well due to problems
with display drivers. Again, if you played games, you would know how
tempermental the display drivers can be.

You're wildly exaggerating what problems there
are, and they're fixable anyway, most obviously
by loading the games from a ram drive.

Essentially because no RAID can make enough
difference to the drive read performance if you
have decent high performance drives in the first place.
Raid can increase read performance,

Not by enough to do anything about VERY SLOW.
so why would this not lead to faster load times?

Basically if it is actually VERY SLOW, no RAID will be
able to make enough of a difference to the read speed.

A ram drive will with very badly written games.
I am planning on having 2 gigs of ram, which is the most I can afford.

Is that with or without RAID and the extra drive ?
However, how much ram do you have in your system?

Irrelevant, I use my systems quite differently.
My system is currently using about 200 gigs of storage. It is not possible to
fill a motherboard with 200 gigs of ram, so obviously the HD still needs to be
used to load information.

Sure, but if you only do that rarely, the speed of doing that doesnt matter.

And you dont need every bit of what is on the hard drive in a ram drive.
 
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G

Gerhard Fiedler

Rod said:
Not if you use the previous main system as the backup.

Not sure which previous system you're talking about. I just put a RAID
controller and an additional drive in my "previous" system.
And many of us have more than one system for various reasons as well.

Lucky you... :)

Gerhard
 
M

Mark

Rod said:
We'll see...




YOU have no idea. It aint the ram use that slows systems
to a crawl, and anyone with a clue can have 4G of ram anyway.

Well, firstly I cannot afford 4 gig, only 2 gig. Second, of course it is
the ram requirements that slows the system to a crawl. Once you run out
of ram, the computer needs to start paging info to the hard disk.
Then keep those in a ram drive, stupid.

You are stupid. You talk about having 4G of ram. How big would the ram
drive be then? Even if you left only 1G for system ram, 3G is not enough
to hold many games.
You're wildly exaggerating what problems there
are, and they're fixable anyway, most obviously
by loading the games from a ram drive.

Again, people who play games will different. Also, loading from a ram
drive does not solve the problems of games directly accessing hardware
and problems with the display drivers (obviously).
Essentially because no RAID can make enough
difference to the drive read performance if you
have decent high performance drives in the first place.

What do you mean by "enough difference"? To me, any speed increase would
be desired.
Not by enough to do anything about VERY SLOW.

Again, I don't understand what you are saying. Are you saying that if
something takes a long time to load from the disk, then raid makes no
difference, and it only improves speed when things already load very
quickly??

I very much doubt this. In fact, the effect of an increase in
performance is likely to be most noticeable on something that is slow,
as this would be the most frustrating wait.
Basically if it is actually VERY SLOW, no RAID will be
able to make enough of a difference to the read speed.

A ram drive will with very badly written games.

Again, firstly a ram drive would not be big enough to hold the game.
Second, you talk about "enough of a difference". What does this mean?
Surely any speed increase is desirable.

Is that with or without RAID and the extra drive ?

I NEED the extra drive for data security, so it isn't an option. Hence,
I don't have the option of using the money towards the extra drive for
ram. Given the extra drive, I would like to be able to see a speed
increase as well.
Irrelevant, I use my systems quite differently.

My point is that I doubt you have 200 gigs of ram in your system, or
indeed anywhere near enough ram to make a ram drive big enough to solve
the problems you are claiming it would solve.
Sure, but if you only do that rarely, the speed of doing that doesnt matter.

And you dont need every bit of what is on the hard drive in a ram drive.

NO. Even if I only load something rarely, when I do I want it to be as
quick as possible.

Again, how big a ram drive is possible, given reasonable money
constraints (eg, <$500). How big a ram drive could you make even if you
choose to spend a lot of money?
 
P

Peter

Looots of RAM. 2, 4 or more GB.
Yes, I used to use a ramdisk. However, I wouldn't now as most things I
would want on there are too big to reasonably fit. For instance, a
single game can be 5 gigs.

No problem. That software supports up to 16GB ramdisk on XP and 64GB on
2003.
 
A

Arno Wagner

Previously Gerhard Fiedler said:
Peter wrote:
But I can do nothing while it doesn't fail -- and that's most of the time
:)
I didn't need a new MoBo. Just added a PCI RAID controller; seems to work
transparently. And that MoBo is pretty old. Are there really issues with
MoBos?

Occasionally. If it works then don't worry. If you get instable behaviour
not due to software, then the mainboard is the next candidate after the
PSU. Using a controller card has the advantage that you do not have
a serious problem if the mainboard dies. And the controller card dying
is significanlty less likely than the mainboard dying, because it is
less complex.

Typical mainboard problems are:
- exploded capacitors
- overheated chipsets

Arno
 
A

Arno Wagner

Of course, if you look up security in the thesauraus, a synonym is
safety. I may not have used the correct technical term, but I think most
people who know English knew what I meant.

Sorry. Did not mean to be too harsh. I work in computer security. We
distinguish strongly between safety (reliability and no danger to the
user) and security (malicious attacks and protection against them).
Both are about damage prevention, but for "security" there is
malicious intent, for "safety" there is not.

You do also:

- The people with the black glases and wire in the ear are
"security" people.

- The matches are "safety" matches.

- A site is "secure" when the dangerous people in it have been
neutralised.

- A site is "safe" when the floor is not about to collapse.

- Border case: When a bomb has been defused is the site
were it is "secure" because the bad people's intent has been
foiled or ist it "save" because nothing can explode anymore?

It sometimes bleeds together, but for technology the distinction is
important and, I think, valid.

Arno
 
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R

Rod Speed

Gerhard Fiedler said:
Rod Speed wrote
Not sure which previous system you're talking about.

The one you were using before the one you are using now.
I just put a RAID controller and an
additional drive in my "previous" system.
Lucky you... :)

Its pretty rare for most that post in here to have just one system.

Mad to have just one if that's what you earn your income with.
 
R

Rod Speed

Mark said:
Rod Speed wrote
Well, firstly I cannot afford 4 gig, only 2 gig.

You still havent said if that is counting
the extra hard drive and RAID controller.

Makes a lot more sense to spend what you
have spent on the second drive on ram instead.
Second, of course it is the ram requirements that slows the system to a crawl.
Once you run out of ram, the computer needs to start paging info to the hard
disk.

Thats why more ram makes a lot more sense
than any RAID if speed is what you care about.
You are stupid.

We'll see...
You talk about having 4G of ram. How big would the ram drive be then? Even if
you left only 1G for system ram, 3G is not enough to hold many games.

Then get more ram 4G, stupid.
Again, people who play games will different.

Only the fools who havent got a clue about the basics.
Also, loading from a ram drive does not solve the problems of games directly
accessing hardware and problems with the display drivers (obviously).

Corse it does if you only run one at a time and fix the load time by
loading them out of the ram drive instead of from the hard drive.
What do you mean by "enough difference"?

To do something about what you claim is VERY SLOW.
To me, any speed increase would be desired.

Makes a lot more sense to increase the speed the most.
Again, I don't understand what you are saying.

That's always been obvious.
Are you saying that if something takes a long time to load from the disk, then
raid makes no difference,

No, that if its currently VERY SLOW, what difference
any RAID makes wont stop it still being VERY SLOW.
and it only improves speed when things already load very quickly??

Nope, never ever said anything like that.
I very much doubt this. In fact, the effect of an increase in
performance is likely to be most noticeable on something that is slow, as this
would be the most frustrating wait.

Yep, and no RAID is going to do much about that.
Again, firstly a ram drive would not be big enough to hold the game.

Then get one that is big enough, stupid.
Second, you talk about "enough of a difference". What does this mean? Surely
any speed increase is desirable.

If its currently VERY SLOW, no RAID will make much difference to that.

A big enough ram drive will make one hell of a difference.
I NEED the extra drive for data security, so it isn't an option.

You dont get much useful security with RAID. You still need proper backup.
Hence, I don't have the option of using the money towards the extra drive for
ram. Given the extra drive, I would like to be able to see a speed increase as
well.

Welp, you wont get much effect with RAID 1.

You'll be lucky if you can even pick it in
a proper randomised double blind trial.
My point is that I doubt you have 200 gigs of ram in your system,

There isnt any point in 200G of ram in your system.
or indeed anywhere near enough ram to make a ram drive big enough to solve the
problems you are claiming it would solve.

It aint a claim, its a fact, it would solve the problem.

You're so poor that you cant afford it ? Your problem.
YEP.

Even if I only load something rarely, when I do I want it to be as quick as
possible.

Then you are out of luck, you're too poor to be able to afford it.
Again, how big a ram drive is possible, given reasonable money constraints
(eg, <$500).

Its just a matter of the cost of the ram and what you can get for that.
How big a ram drive could you make even if you choose to spend a lot of money?

There isnt any practical limit with 2003, plenty enough
to load all your games into it and run them from there.
 
M

Mark

Peter said:
No problem. That software supports up to 16GB ramdisk on XP and 64GB on
2003.

That would be cool. However, on the website, it lists as 4Gb the maximum
for XP. More importantly, the ram limitation I was concerned with is how
much ram you can get on the motherboard, eg, 4 slots, 1 gig modules -
how does one get a 16GB ramdisk without spending ridiculous $$$'s?
 
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M

Mark

Arno said:
Sorry. Did not mean to be too harsh. I work in computer security. We
distinguish strongly between safety (reliability and no danger to the
user) and security (malicious attacks and protection against them).
Both are about damage prevention, but for "security" there is
malicious intent, for "safety" there is not.

You do also:

- The people with the black glases and wire in the ear are
"security" people.

- The matches are "safety" matches.

- A site is "secure" when the dangerous people in it have been
neutralised.

- A site is "safe" when the floor is not about to collapse.

- Border case: When a bomb has been defused is the site
were it is "secure" because the bad people's intent has been
foiled or ist it "save" because nothing can explode anymore?

It sometimes bleeds together, but for technology the distinction is
important and, I think, valid.

Arno

Oh yes, I recognized the distinction when you made it. Just when I made
the original comment I wasn't thinking along those lines.
 

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