Poor raid 1 performance?


M

Mark

Hi there,

I am planning on building a new computer system. Given the current cheap
price and massive capacity of hard drives, I am thinking of using a raid
array.

To me, raid 1 seems the ideal solution. Raid 1 greatly improves data
security, which is very important to me (and why I would never go with
raid 0). Theoretically, the performance of raid 1 should also be what I
want. Reads can be split across the two drives, leading to greater read
performance, while write performance might be slower. Given the way I
use the computer, read performance will help when it boots up, loads
applications, loads games, etc. On the other hand, the poorer write
performance will be less of an issue as much less is written to the disk
during typical use, and I tend to just leave the computer when
installing new programs (when large amounts of information does need to
be written to the disk).

Despite raid 1 seeming to be ideal, the read performance on current
motherboard raid chipsets shows little to no improvement compared to
that of a single drive:

http://techreport.com/reviews/2004q2/chipset-raid/index.x?pg=1

Is it possible to get improved read performance using raid 1??
 
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B

Bruce T. Berger

Mark said:
Hi there,

I am planning on building a new computer system. Given the current cheap
price and massive capacity of hard drives, I am thinking of using a raid
array.

To me, raid 1 seems the ideal solution. Raid 1 greatly improves data
security, which is very important to me (and why I would never go with
raid 0). Theoretically, the performance of raid 1 should also be what I
want. Reads can be split across the two drives, leading to greater read
performance, while write performance might be slower. Given the way I use
the computer, read performance will help when it boots up, loads
applications, loads games, etc. On the other hand, the poorer write
performance will be less of an issue as much less is written to the disk
during typical use, and I tend to just leave the computer when installing
new programs (when large amounts of information does need to be written to
the disk).

Despite raid 1 seeming to be ideal, the read performance on current
motherboard raid chipsets shows little to no improvement compared to that
of a single drive:

http://techreport.com/reviews/2004q2/chipset-raid/index.x?pg=1

Is it possible to get improved read performance using raid 1??

No! Raid 1 exists solely for data preservation ...you may be thinking of
RAID 1+0 which will give you redundancy plus a performance gain without
requiring a RAID 5 capable controller but as far as RAID 1 is concerned you
are mistaken in your belief that it will or should boost performance.

btb
 
R

Rod Speed

Mark said:
Hi there,

I am planning on building a new computer system. Given the current
cheap price and massive capacity of hard drives, I am thinking of
using a raid array.

To me, raid 1 seems the ideal solution. Raid 1 greatly improves data
security, which is very important to me (and why I would never go with
raid 0). Theoretically, the performance of raid 1 should also be what
I want. Reads can be split across the two drives, leading to greater
read performance, while write performance might be slower. Given the
way I use the computer, read performance will help when it boots up,
loads applications, loads games, etc. On the other hand, the poorer
write performance will be less of an issue as much less is written to
the disk during typical use, and I tend to just leave the computer
when installing new programs (when large amounts of information does
need to be written to the disk).

Despite raid 1 seeming to be ideal, the read performance on current
motherboard raid chipsets shows little to no improvement compared to
that of a single drive:

http://techreport.com/reviews/2004q2/chipset-raid/index.x?pg=1

Is it possible to get improved read performance using raid 1??

Why do you actually need improved read performance ?
 
A

Arno Wagner

Previously Mark said:
Hi there,
I am planning on building a new computer system. Given the current cheap
price and massive capacity of hard drives, I am thinking of using a raid
array.
To me, raid 1 seems the ideal solution. Raid 1 greatly improves data
security,

It improves safety. It does nothing at all for security.
which is very important to me (and why I would never go with
raid 0). Theoretically, the performance of raid 1 should also be what I
want. Reads can be split across the two drives, leading to greater read
performance, while write performance might be slower. Given the way I
use the computer, read performance will help when it boots up, loads
applications, loads games, etc. On the other hand, the poorer write
performance will be less of an issue as much less is written to the disk
during typical use, and I tend to just leave the computer when
installing new programs (when large amounts of information does need to
be written to the disk).
Despite raid 1 seeming to be ideal, the read performance on current
motherboard raid chipsets shows little to no improvement compared to
that of a single drive:

Is it possible to get improved read performance using raid 1??

Maybe, but it is not necessaruly done. E.g. Linux software RAID does
not speed up reads either. I don't quite know why, but there
is RAID10 where you combine a RAID0 layer and a RAID1 layer to get
speed and reliability, but also wor writes. My guess is that
speeding up reads is not enough of an issue to do RAID0 like
reading into the drivers/chips just for reading.

Arno
 
G

Gerhard Fiedler

Bruce said:
No! Raid 1 exists solely for data preservation ...

Well, actually /my/ performance increased since I use RAID1 and don't have
to worry about the next disruptive hard drive crash anymore :)

Really, IMO there's little reason to run any computer that's used to store
critical data without RAID1 (or one of its derivatives).

Gerhard
 
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B

Bob Willard

Bruce said:
No! Raid 1 exists solely for data preservation ...you may be thinking of
RAID 1+0 which will give you redundancy plus a performance gain without
requiring a RAID 5 capable controller but as far as RAID 1 is concerned you
are mistaken in your belief that it will or should boost performance.

btb
It is certainly possible with RAID1 to get better read throughput than
with a single HD, since RAID1 has twice as many on-disk read channels and
twice as many seek mechanisms. But, any increased read performance depends
on the workload (to have multiple reads outstanding) and on the RAID driver
(to not serialize the multiple outstanding reads).

I do agree that the primary reason for deploying RAID1 is data integrity
rather than performance, but modest performance gains have certainly been
measured (by me and by others) with good RAID1 implementations.
 
P

Peter

Well, actually /my/ performance increased since I use RAID1 and don't have
to worry about the next disruptive hard drive crash anymore :)

But it doesn't mean that you should do nothing when one drive fails.
Really, IMO there's little reason to run any computer that's used to store
critical data without RAID1 (or one of its derivatives).

As little as a hundred bucks for a second disk and a new MB, if current does
not support RAID.
 
A

Antoine Leca

since RAID1 has twice as many on-disk read channels
and twice as many seek mechanisms.

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
 
P

Peter

Why do you actually need improved read performance ?

He wants his computer to boot up faster and load games faster. To some
people an extra 10-20 seconds is eternity.
 
P

Peter

To me, raid 1 seems the ideal solution. Raid 1 greatly improves data
It improves safety. It does nothing at all for security.

He probably meant security in a broader sense. Like "it should be there,
where I have left it".
 
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P

Peter

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.

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.
 
R

Rod Speed

Gerhard Fiedler said:
Bruce T. Berger wrote
Well, actually /my/ performance increased since I use RAID1 and don't
have to worry about the next disruptive hard drive crash anymore :)
Really, IMO there's little reason to run any computer that's used
to store critical data without RAID1 (or one of its derivatives).

Corse there is if the data activity isnt high and normal backup
will be completely adequate. Normal backup has a number of
advantages over any RAID, most obviously any stupidity or
infection doesnt get propagated to all copys virtually instantly.

Yes, you can certainly have both, but most
dont actually need the advantages of RAID.
 
R

Rod Speed

He wants his computer to boot up faster

The obvious way to make it boot much faster again is
to minimise the number of boots and to hibernate instead
of shutdown when you do need to shut the system down.
and load games faster.

The obvious way to fix that problem is to keep
them loaded so they are an instant switch away.
To some people an extra 10-20 seconds is eternity.

Improved read performance isnt the only way to fix that. And
its perfectly possible to do much better than any RAID config
can do on that. Not a shred of rocket science required at all.
 
R

Rod Speed

He probably meant security in a broader sense.
Like "it should be there, where I have left it".

But it doesnt help with real security, doing
something really stupid, or getting infected etc.
 
G

Gerhard Fiedler

Peter said:
But it doesn't mean that you should do nothing when one drive fails.

But I can do nothing while it doesn't fail -- and that's most of the time
:)
As little as a hundred bucks for a second disk and a new MB, if current does
not support RAID.

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?

Gerhard
 
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P

Peter

Well, actually /my/ performance increased since I use RAID1 and don't
have
But I can do nothing while it doesn't fail -- and that's most of the time
:)

That is what most of the people do. Even those with PCs with single drives.
I didn't need a new MoBo. Just added a PCI RAID controller; seems to work
transparently.

You can add RAID controller, sure.
And that MoBo is pretty old. Are there really issues with
MoBos?

Not less than with HaDrives
 
G

Gerhard Fiedler

Rod said:
Corse there is if the data activity isnt high and normal backup
will be completely adequate.

That's why I wrote "critical 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. Otherwise, I could easily have a day downtime (need to get drive,
restore last image, redo all the work that happened afterwards). 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...)
Normal backup has a number of advantages over any RAID,

RAID1 is no substitution for backup, of course, it's an enhancement for an
adequate backup strategy.
Yes, you can certainly have both, but most dont actually need the
advantages of RAID.

Most don't, but then most don't create critical data. I'd recommend it for
everybody who creates critical data.

Gerhard
 
M

Mark

Arno said:
It improves safety. It does nothing at all for security.

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.
 
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M

Mark

Rod said:
The obvious way to make it boot much faster again is
to minimise the number of boots and to hibernate instead
of shutdown when you do need to shut the system down.

My computer hasn't always recovered from hibernation okay, something to
do with the power management. Hence, I am hesitant to use it. Also, I do
like the idea of rebooting regularly to stop the system becoming bloated
with memory resident programs that I don't need.
The obvious way to fix that problem is to keep
them loaded so they are an instant switch away.

Okay, you obviously don't play games. First, having them stay in the
background quite often reduces the computer to a crawl. Second, even if
you are in the game, level loads (and saving and loading your position)
can be very slow.
Improved read performance isnt the only way to fix that. And
its perfectly possible to do much better than any RAID config
can do on that. Not a shred of rocket science required at all.

I'd be interested in other techniques. What do you suggest?
 

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