Re: limits on raid

[david@lang.hm]

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