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Raid 5 slow sequential write speed

Posted on 2006-06-14
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Last Modified: 2010-03-16
I have an hp ProLiant server with 3 72.8 G ULTRA320 SCSI drives set up as a RAID 5 array.  When I run a PassMark performance test on the disk it gives me a 6.3 MBytes/Sec write speed.  A comperable machine gives a write speed of 56.4.  Does anyone have any tips to troubleshoot this problem?
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Question by:mhalp200
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by:Callandor
ID: 16905537
Check the status of the array and make sure it is not in a degraded state.  You should also run diagnostics on each drive from the controller, to see if any are failing.  Try another cable as well, check if the SCSI ids are correctly jumpered for all devices, and make sure the termination is set properly (one on each end of the cable, either electronically or otherwise).
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by:mhalp200
ID: 16905658
I ran an Array Diagnostic utility.  Id did not report any errors with the array.  It did however, report a sector size of 512 bytes, however, I had changed it, and chkdsk reports 4096 bytes.  Can this be related to the slowness.

I will check the cabling later.

Thanks
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by:Callandor
ID: 16905689
I've never tried a sector size other than 512; was there a reason you changed it?
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by:scrathcyboy
ID: 16908958
The benchmark will report a 10x slowness when it is (1) checking the raid for consistency, (2) writing the checksums, (3) refeshing the RAID redundancy, (4) have a driver that is not compatible with the OS, or (5) having sector read issues.  You should continue to test the array, and if the situation does not improve in a day or so, you should look at the drives in windows, make sure the RAID drivers are OK.  And if you continue to get problems, as long as there is no data lost or missing, run checkdisk.  If it still does not improve performance, look and upgrading the RAID BIOS from the HP website.  And if all that fails, you probably have a failing disk which is causing repeated reads.  Do you hear clicking from the drives?  If so, one is haing sector read errors, so it is time to replace it.  This RAID should do 65Mb ++.
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by:mhalp200
ID: 16910495
I noticed that through the device manager in control panel, wrte caching is not enabled.  Could this be causing the slowness.

By the way there really is slowness - it noticed it before running the diagnostic utility.


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by:Callandor
ID: 16911736
Write caching is in the controller, and you should still see good results on reads.  I would say take apart the array and test the performance with each drive separately.
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by:Psyco_666
ID: 16919482
Have you looked at which way the cache is oriented? read vs write. Is this a 5i or a 5300 controller?
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macaulish earned 500 total points
ID: 16922114
You cannot enable write caching through windows, you have to do it at the controller level.  If you have the 6i controller you won't be able to enable write caching unless you have a battery backed write cache enabler.  Raid 5 is not the best configuration for a server if you plan on writing the the disk a lot but if you purchase the HP 128MB BBWC and configure write caching you will see improved performance.

Hope this helps

Mike
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by:mhalp200
ID: 16927294
Mike

Thanks,

I noticed before your post that windows does not allow me to enable write caching.  I'll purchase the HP 128MB BBWC.  If this allows me to enable toe wriote caching, and it greatly improves the sequential write speed, I will give you the points.
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Author Comment

by:mhalp200
ID: 16955584
It worked!

I bought the HP 128MB BBWC and configured write caching.  I now get a benchmark speed of over 56.


Thanks



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by:tomsmorgan
ID: 27696861
Mhalp200,
Did you have to back up & restore to replace card, I have the same problem write 9mb/s read 111mb/s
with perc4/sc
SCSI is hard to image and restore
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