Raid 5 on 641 controller incredibly slow

[David Martino]

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?

[raadek]

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

[David Martino]

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?

[raadek]

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!

[David Martino]

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