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SubjectRe: limits on raid
On Mon, 18 Jun 2007, Brendan Conoboy wrote:

> david@lang.hm wrote:
>> in my case it takes 2+ days to resync the array before I can do any
>> performance testing with it. for some reason it's only doing the rebuild
>> at ~5M/sec (even though I've increased the min and max rebuild speeds and
>> a dd to the array seems to be ~44M/sec, even during the rebuild)
>
> With performance like that, it sounds like you're saturating a bus somewhere
> along the line. If you're using scsi, for instance, it's very easy for a
> long chain of drives to overwhelm a channel. You might also want to consider
> some other RAID layouts like 1+0 or 5+0 depending upon your space vs.
> reliability needs.

I plan to test the different configurations.

however, if I was saturating the bus with the reconstruct how can I fire
off a dd if=/dev/zero of=/mnt/test and get ~45M/sec whild only slowing the
reconstruct to ~4M/sec?

I'm putting 10x as much data through the bus at that point, it would seem
to proove that it's not the bus that's saturated.

David Lang
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