Slow RAID1 with gmirror

Hr. Daniel Mikkelsen daniel at copyleft.no
Sat Jul 22 13:44:35 UTC 2006


Hi.

I've been setting up some gmirror based software RAID1s lately, and I
keep running into some odd behaviour.

Writing to the RAID1 runs at near to normal rates, as expected.

But reading from the RAID1 runs at half the normal rates, while I
expected to get double rates.

I've tested this on 6.0, 6.1, with PATA and SATA drives, and I
consistently get the same results.

I've tested with the same hardware running Linux 2.6 with software RAID1
and there I get the expected double rate.

I've tried all the available balance algorithms, and none of them help.

I haven't tried with SCSI disks.

I'm thinking that it might be the test I'm running that's a corner case,
I simply dd to or from the filesystem with various settings for bs=.

Is this a know issue? Is it an issue at all?

-- 
Daniel Mikkelsen
Copyleft Software AS


-- 
Daniel Mikkelsen
Copyleft Software AS


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