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IBM server 3650 M2 with DS3400 SAN configuration

Posted on 2009-12-19
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Hi All,
  I have setup a SQL 2005 server in my IBM 3650 server connected with Fiber card to DS3400 SAN, my SAN is configured with 5 Disks each is 1 TB as RAID 5. the disks are SATA. my question is I have my 120 GB SQL Database which i feel its very slow in all the transactions.
can someone advise in what is the cause of the slowness, I have just 50 users accessing the Database.  need help

Thanks
 
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Question by:ITMaster1979
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David earned 400 total points
ID: 26087287
Is NTFS allocation size = 64KB, and is the stripe size of each of the disks = 16KB (4 disks then total to 64KB)?  If not, then you are incredibly inefficient at I/O.

So if you have RAID configured so each disk reads/writes 32KB at a time, then if the NTFS just needs 4KB worth of data, each disk in the RAID will actually read 32KB, meaning you are reading 8X too much data.  
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by:andyalder
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SATA and RAID 5, that sucks. 4 physical I/Os per write with RAID 5. You should be using RAID 10 with fast SAS disks.

You should generally use a stripe element size of 64k for SQL, then one disk will satisfy most single I/Os leaving the other disks to satisfy other I/Os. You also have to use diskpart to align or you may end up with 2 disks involved in a single SQL IO.

http://technet.microsoft.com/en-gb/library/cc966414.aspx (read the bit entitled Sector Size vs. Stripe Size) but read the whole white paper.

Is your DS3400 dual controller? If single controller then write cache is disabled by default due to no second controller to mirror cache to.

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by:David
David earned 400 total points
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5 physical I/Os with RAID5, but who's counting :)

writeback is write cache turned on, writethru is write cache disabled (all at the controller), there is also disk-level write cache enable, but obviously don't use any write caching without a  UPS, unless there is no UPs on the PC, then it doesn't matter anyway.

Of course it could be a lot of things, it would be helpful to know specifics of what  you benchmarked, how you did it and the numbers you are getting.  For all we know problem is not with I/O at all and if you added a GB or so of RAM then everything will be fine.
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by:andyalder
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No, it's 4. Read data, read parity, xor, write data, write parity.
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by:ITMaster1979
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Hi All,

  Sorry its SAS disks and yes I do have two controllers, any help

Thanks
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by:ITMaster1979
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Hi All,

 My server is quad core with 10 GB RAM.
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by:ITMaster1979
ID: 26087831
Hello, I just login in to SAN Manager , its SATA.
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by:David
ID: 26088639
well it can be 4 or 5, depending on firmware.  some implementations check XOR parity on reads, and do further IOs to fix it if incorrect.  ideally if you value integrity over performance, you want this extra IO ... as it also clears out unrecoverable IOs on parity blocks which would otherwise go unnoticed
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by:andyalder
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If it was 100% read you'd be getting about 80 * 4 IOPS = 320 IOPS, 100% write you'd be getting about 80*5/4=100 IOPS.

If you remove one disk and make it RAID 10 instead you'll get about 80*4=320 IOPS if 100% read, 80*4/2=160 IOPS.

So the first thing I would do is backup, delete the array, create a new one with 4 disks in RAID 10, reformat using diskpart align=64 and restore. You can use the other disk as a hot spare.
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