What speed to expect from RAID 5?

never say never · 09-16-2010, 11:32 AM

I thought you said even Raid 10 was slower than the test report I found, but that it was much closer to normal. May be something silly like crosstalk on a trace on the card or something slowing down one port hard to say but I found a lot of consumer reviews talking about issues with port 4, even after changing out the cables and drives, with / without backplane . . .

I just read an article last night that Intel is going to support SAS on the motherboard. 10 years ago they scoffed at software raid. They figure with the newer processors with multiple cores RAID 5 can be handled with 2 - 3 % of CPU and software raid is actually faster than some raid cards.

I am interested to know what you find out, so please post back your results.

Skaperen · 09-16-2010, 01:00 PM

Here are stats with a config using RAID 5 on just the first 3 drives:

Code:

/dev/sda: drives 0 1 2, RAID 5, 256K stride, no write cache, balanced
/dev/sdb: drive 3, single, no write cache
/dev/sda read:    267.976 MB/sec    blocksize  1048576
/dev/sdb read:    135.881 MB/sec    blocksize  1048576
/dev/sda write:    16.958 MB/sec    blocksize 16777216
/dev/sdb write:   120.460 MB/sec    blocksize 16777216
/dev/sda read/write:  15.802
/dev/sdb read/write:   1.128

Writing on this config is actually faster.

FYI, the BIOS management identifies drives and PHYs as 0 through 3.

jefro · 09-16-2010, 07:42 PM

I meant that many posts refer to the number 4 connection being an issue. It was not a joke.

never say never · 09-20-2010, 07:43 PM

Why no write cache?

Any more progress?