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New IBM server slow disks!!!

Hi, I have just setup a new IBM x346 server where I have a serveraid 6M controller card (with 128mb of cache) I have 8 disks on the rack (8 * 36gb 15krpm)
I have 2 channels connected between the rack and the controller. I have 4 disks in raid5 (2 disks on each channel)
2 in raid 0 (1 disk on each channel)
and 2 in raid 0 (1 disk on each channel) but the disk throughput is slow with 50% read+ 50% writes!!!! (iometer used) 1 local disk has a throughput of 12mb/s
a raid 0 on the rack go up to 17mb/s
the raid 5 = 15mb/sec 4 disks in raid 0 go to 22mb/s!!! if I test 100% read only, then I go to :
1 local disk= 80mb/s
raid 0 = 80mb/s
raid 5 = 25mb/s wow… the raid 5 don’t change… the 2 disks raid 0 don’t provide any advantage against a single disk!!! if I read (100% read) my raid 5 + raid 0 + raid 0 at the same time the throughput = 100mb/s !!!!! while I expect : 80 + 80 + 25 = 185mb/s!!! I don’t understand whats appends…
specially with the raid 0 config.
if the 2 disks of the raid 0 are on the same channel, the performance slow down to 8mb/s half of the speed of 1 disk!!! does the dual channel link is the problem?
all the drivers & firmware are uptodate thanks for your help. jerome.

http://www.sqljunkies.com/Article/D1B7C756-4725-4D31-A53D-C0A47976E6BB.scuk to check for more information. Satya SKJ
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But this doesn’t help me in the way of:
when I add disks in a Raid 0 the performance is not improved and, sometimes, is degraded compared to a single disk!!! for example, a 100% read test demonstrate that a single disk go to 80mb/s and a raid 0 go to… 80mb/s while 4 disks in raid 5 go to 25mb/s!!!!! do you think its good????

what test are you doing?
only look at MB/sec when doing sequential
if random, then don’t bother looking at MB/sec, just look at IOPS, example: 8K random IO
expect 200 IOPS at moderate queue depth
this is 1.6MB/sec per disk
well… after some tests and changing in the config I have found a good solution. now I’m using the SQLIOStress tool, which simulate an SQL Server load.
I have changed my raid 0 to a raid 00, a spanned array configuration. (finally its the same result has a raid 0)
the test jump from 4mb/s to 31mb/s for the raid!!!
my raid 5 go to 27mb/s
and a simple disk go to 8mb/s. this 31mb/s on 2 disks outperform another server where I have 4 disks in raid 10 on a SAN (result = 22mb/s) Now I’m testing when I access the raid 5 & raid 00 at the same time. the usage is a small data warehouse.
I’ll put the tempdb on the raid 00 and the DW himself on the raid 5
and the other raid 00 will host staging & temporary databases

Well… after a lot of tests and changes in the config… writing access is good on the raid disks, but the read access is poor!!!
with iometer… Setup: 1 local disk no raid, no cache
8kb, 50% random, 100% read -> 350 io/sec; 3mb/s
8kb, 50% random, 100% write -> 680 io/sec; 5.5mb/s Setup: 4 disks in raid 10, 128 mb cache
8kb, 50% random, 100% read -> 250 io/sec; 2mb/s
8kb, 50% random, 100% write -> 1200 io/sec; 9.5mb/s writing process is excellent (twice the performance of 1 disk)
but reading process…. no comment… which parameter could impact the reading step?

Are you using the RAID controller card that came with the server willgart? MeanOldDBA
[email protected] When life gives you a lemon, fire the DBA.
its a second controller.
there is an internal default controller, and we have added a second one to connect the external disks.
its a ServeRaid 6M controller. (IBM Server) we have applied some changes in the hardware config and I’ll test this.

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