topic Re: Raid 5 on 641 controller incredibly slow in Disk Enclosures

Raid 5 on 641 controller incredibly slow

David Martino — Tue, 28 Mar 2006 09:58:12 GMT

ProLiant ML350 G3, 2-XEON 3.066GHz, 1GB RAM.
RAID 5 array on a 641 controller w/4 146GB U3 SCSI drives, 64KB stripe size. Copying a file internally, the speed averages about 4MB/sec. It may have been this way since installed. The array controller does not have battery backed cache,not was this ever suggested by our HP authorized vendor.
Can this possibly be normal behavior for this machine? If so, why did they put GB NICs in the thing?

Re: Raid 5 on 641 controller incredibly slow

raadek — Thu, 30 Mar 2006 05:28:55 GMT

RAID 5 per definition has very large write performance overhead. Hence using a battery backed write cache (BBWC) is generally a prerequisite.

I see two solutions:
a) upgrade your controller with BBWC
b) migrate RAID level to 1+0 which will steal some capacity (only half available), but delivers much better performance

Regards,
Radek

Re: Raid 5 on 641 controller incredibly slow

David Martino — Thu, 30 Mar 2006 08:36:15 GMT

The cache has been ordered, although I still find it hard to believe that it should be this slow without it. Any comments, white papers, etc. that anyone can point to re:optimum stripe size?

Re: Raid 5 on 641 controller incredibly slow

raadek — Thu, 30 Mar 2006 08:54:02 GMT

There are some interesting points at the bottom of this page:
http://www.informit.com/articles/article.asp?p=359414&seqNum=3&rl=1

But do not expect any magic trick - BBWC is a necessity for RAID5!

Re: Raid 5 on 641 controller incredibly slow

David Martino — Thu, 30 Mar 2006 09:50:43 GMT

Thanks. We will be putting it in on Tuesday or Wednesday of next week.