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Too slow Raid 5 on Smart Array 641

Jerome Poudou
Occasional Visitor

Too slow Raid 5 on Smart Array 641


I'm suffering an amazing slow performance with 5 disks in raid 5 on my Smart Array 641.
(5 * 36Gb 10Krpm disks)

When I try to copy big files other the 1Gbps network I stop the transfert after 10 minutes!!!
Copying the same file on another server takes less then 2 minutes (1 SATA2 disk!!!!)

The windows performance counters display that the % disk time is greater then 1000%, the Avg Disks Queue length is greater then 22.
Copying the file locally produce good performance counter values (queue = 2-3; % disk time = 30-35%) but the copy takes again more then 10 minutes!

The Hd Tune utility result is 40Mb/s for my Raid 5, while my standalone SATA2 disk result is 50mb/s.

My drivers are up-to-date.

what can I do???
Honored Contributor

Re: Too slow Raid 5 on Smart Array 641

Do you use / have you got the battery backed write cache?

RAID 5 due to its algorithm has a large write overhead & in most scenarios is much slower for writing than a single drive if implemented without a write cache.
Don't panic! [THGTTG]
Honored Contributor

Re: Too slow Raid 5 on Smart Array 641

Yes, this has been proven to produce an 8x increase inperformance on writes due to the cache. Another issue comes up if Windows is istall on the RAID 5 set, with Windows again adding to the overhead with it's continued writes of the virtual file.
1-add the Battery/write cache module.
2-move Windows to a stand alone drive off of the RAID controller, it has enough to do.
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