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IO problems

Posted on 2005-03-17
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Last Modified: 2010-04-18
Hello,

I am having some serious IO problems on a ML350 with 2003 running on it.

Have a Raid Controller in it  (64 mb cache). 5 drives (2 mirrored, 3 Raid 5)
Dual Xeon 3.06
We have sql server 2000 running on it, and the performance on it is terrible.

We ran a SQL server IO test on it, and my 1.6ghz laptop and the laptop beat by a factor of 5 in read/writes per second.

I had a HP employee in today, and he replaced everything but the system board and drives. No changes.

After all this he decided that the server is running fine. I will not accept that.

What other IO tests can i run on this? I want a generic IO test, to see what the problem is.

 BTW, we also booted from an XP boot Disk, and the performance was the same on the server, so the OS can be ruled out.
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Question by:91mustang
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by:CHurst5841
ID: 13571514
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mysticaldan earned 500 total points
ID: 13581255
Did u try  a BIOS update?? Are all the drivers current? Any chance that a drive is busted leading to  choking of the flow of data. Since u have them RID'ed chances are that u shud actually start with a single hard disk and strt eliminating the bottleneck. With so many hard disks it wud be virually impossible to narrow it down to the problem area.

Also with so many hard disks a RAID5 will have the avantage of Higher I/O rate for writing data and since no dedicated parity disks, no data loss for any disk failure but the negtive is that its slow. A RAID3 wud be faster. SInce a part of the data is written onto the parity so it slows down the operation. Add to this that the parity is spread out over many disks and the system cud slow down for fragmentation reasons. Are ur disks defragmented?  Now again u have  mirror that must be written to and a RAID5 where u need to have data written to at a penalty for the parity.

My suggestion is to have a RAID3 rather than a RAID5 and make sure ur disks are properly defragmented. The reason ur laptop beat this server is cause ur laptop is not having data safegaurd mechanisms and is hence fast. Also do u have write behind enabled for ur controller. CHeck the manual for that. It can seriuosly affect performance if its disabled although its said to be safer but I still reccomend enabling it since the performance gains are quite perceptible.

Dan
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by:91mustang
ID: 13582522
hi Dan,

All the drivers are ok, and bios is up-to date. I think you are correct about the data safeguard. I spoke with the HP rep, and he mentioned that since we oly have a 64mb cache on the server, we are getting no write cache, only read. He is going to lend us a 128mb upgade cache on monday to see the performance difference.

I will post back when i see the results.
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by:mysticaldan
ID: 13585472
Even with the 64 Mb cache it shud have 'write behind' enabled. Its a method of posting cache and improves performance dramtically. Even if u put in an additional 128 Mb of cache without write behind enabled the performance wont jump higher. With a RAID0 and a RAID5 on u cud do well with Write Behind enabled. Contact the HP dude for hw to go abt it or u must have had a utility that helps you do that. With Write Cache enabled even with 64 MB cache u'll see a marked difference in performance for sure.

Dan
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by:91mustang
ID: 13586175
With only the 64mb, the card can only use it for Read cache, when we add an additional 128, we can set a read/write ratio.
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by:mysticaldan
ID: 13588666
great. then once u have the read:write ratio set i am sure u'll find ur performance up by a signifactant ratio.

Dan
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by:91mustang
ID: 13597529
Yeah, the 128 mb additional increased performance by a factor of 20!!

For $400 CDN, I will take it anytime.

thanks for the assistance.

91mustang
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by:mysticaldan
ID: 13598456
And to think that people dont pay much attention to write behind caching ;-)

I am glad u have it sorted out now.

Cheers!!
Dan
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