topic Re: Too slow Raid 5 on Smart Array 641 in Disk Enclosures

Too slow Raid 5 on Smart Array 641

Jerome Poudou — Sun, 23 Apr 2006 09:43:19 GMT

Hi,

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???
thanks.

Re: Too slow Raid 5 on Smart Array 641

raadek — Mon, 24 Apr 2006 03:16:13 GMT

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.

Re: Too slow Raid 5 on Smart Array 641

e4services — Mon, 24 Apr 2006 08:37:41 GMT

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.
So,
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.