Raid 5 disk speed performance question

[zzyzzx]

What kind of performance should I be getting from a RAID 5 disk array with 4 hard drives rated at 6GB/sec in each array (total of 4 arrays on a Promise card). It's on a 64 bit Linix system and when I run the dd disk speed test I'm getting abotu 1.3GB /sec/

[neomaine]

What kind of performance should I be getting from a RAID 5 disk array with 4 hard drives rated at 6GB/sec in each array (total of 4 arrays on a Promise card). It's on a 64 bit Linix system and when I run the dd disk speed test I'm getting abotu 1.3GB /sec/

I'd say that was pretty darn good. That rating of 6GB/sec is probably not the sustained read rate anyway. Once the read cache is used up you're down to strict disk i/o. You should be pretty happy. At 1.3gb/sec your probably maxing out on the bus/backplane speed.

Note: You mean 4 drives in a 5 disk array, not 4 arrays. Though it may be a naming convention with Promise that I'm not familiar with. This gives you the space of three usable drives and with fourth used as the parity drive. Great for read performance with a slight hit on write performance. (Takes a little extra work to create the parity stripe.)

[zzyzzx]

OK, correction. 6GB/sec is interface. Actual disk speed rating in 600MB/sec. Light bulb finally went off earlier today and I checked a volume not on the RAID array and got numbers about half what I'm getting from the RAID array, so I guess it really is working right.

[Cornucopia]

As luck would have it, I'm right in the middle of repairing 2 Servers that had RAID 5 systems (electrical problems), and after having one server be irreparable (sp?) because more than 1 drive went bad during rebuild, I've come to the conclusion that it's faster and safer to go with RAID 10. Once they're all up and running/serving again, I post a benchmark of their speeds. Read online about how RAID 5 isn't really secure anymore w/ large HDs, and even RAID 6 won't be in 5-10 years.

Just a suggestion.

Scott

(thank God I've got backups!)