Robert Bouillon

RAID Guru help please....

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I'm currently working on a Production SQL server with 6 15k U320 SCSI hard drives on an IBM RAID controller in RAID 5.

We've been generally dissapointed with the performance of the machine, and historically have had nothing but problems with the machine.

I ran HD Tach as well as some other utility called DiskBench. HD Tach showed a burst rate < 100MB/s, a seek time of 6ms, and the graph showed an average of 60 MB/s read rate. It was close to how my laptop rated....

I almost cried.

I hoped that HD Tach just had prejudice against RAID 5 or the controller for some reason, so I dug up another bench tool called DiskBench.

Multi-threaded reads rated < 20MB/s. Multi-threaded writes were around 40MB/s. Something seemed really screwy here.

What's the best way to bench my array? What kind of performance should I expect from the array? Is HD Tach generally accurate?

If so, I need to call IBM and cause a ruckus.

Thanks in advance.

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Older versions of HD Tach were absolute rubbish for benching RAID arrays, newer versions are better but I would still not touch it with a twenty foot bargepole.

SiSoft's Sandra is OK for synthetic becnhes, not great, but works OK on RAID.

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It's very simple; copy a few random files on your PC (a few GB) and copy the same files on your laptop (more sure no files were cached). Compare the difference. Although not a perfect test, it should give you some indication as how fast (or slow) your drive is working. Who needs these dumb tests anyways, all what counts is real-time performance and for this a stopwatch will do just fine in any single user environment.

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It's very simple; copy a few random files on your PC (a few GB) and copy the same files on your laptop (more sure no files were cached). Compare the difference. Although not a perfect test, it should give you some indication as how fast (or slow) your drive is working. Who needs these dumb tests anyways, all what counts is real-time performance and for this a stopwatch will do just fine in any single user environment.

Thanks. I tried the file copy method with a large (1GB File).

I copied from a RAID 5 array on channel #2 to the RAID 1 array on channel #1.

The 938k (exactly) file copied in about 35 seconds. I'm sure the file was not cached. I would expect copying from one U320 channel to another U320 to be faster than that. That puts us at about ~35 MB/s.

Am I mistaken or is this abnormally slow? I'm thinking the channel has been kicked to wide (40MB/s)?

It's very simple; copy a few random files on your PC (a few GB) and copy the same files on your laptop (more sure no files were cached). Compare the difference. Although not a perfect test, it should give you some indication as how fast (or slow) your drive is working. Who needs these dumb tests anyways, all what counts is real-time performance and for this a stopwatch will do just fine in any single user environment.

Thanks. I tried the file copy method with a large (1GB File).

I copied from a RAID 5 array on channel #2 to the RAID 1 array on channel #1.

The 938k (exactly) file copied in about 35 seconds. I'm sure the file was not cached. I would expect copying from one U320 channel to another U320 to be faster than that. That puts us at about ~35 MB/s.

Am I mistaken or is this abnormally slow? I'm thinking the channel has been kicked to wide (40MB/s)?

Also, it's a ServeRAID 6M with a 256MB Cache. The card is on a 133MHz PCI-X bus.

Thanks.

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Hello, bonjour ;-)

I have a ServeRAID-6M at home on a limited 64bit/66MHz PCI slot.

This is on a home machine, and I have tried various configs with 6 disks, all 15kRPM Fujitsus MASxxxx.

Is your RAID5 a 5E or 5EE? What is your stripesize,Readcache and writecache settings? Are there any background task running on your array/controller?

For your environment (SQL) you should bench/ characterize your setup

with IOmeter or Intel IPEAK Storage Performance Toolkit (not supported by Intel now) tweakers.net use this kit and have many load profiles that would help you get a better grasp of what works for your setup.

You could also try to find hints/help at:

http://www.sql-server-performance.com/

http://www.enterpriseitplanet.com/

http://www.enterprisestorageforum.com/

you could look at IBM, on SQL tuning tips:

http://www.ibm.com/Search/?q=sql+tuning&am...c=us&en=utf

Check this old discussion on ServeRAID-6M performanbce:

http://forums.2cpu.com/showthread.php?t=57...ht=serveraid-6M

I hope this will help you find a solution or give you ideas on finding your solution,

JB

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