Re: limits on raid

[david]

On Mon, 18 Jun 2007, Brendan Conoboy wrote:

> david@xxxxxxx wrote:
> >  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.
>
> I am unconvinced.  If you take ~1MB/s for each active drive, add in SCSI 
> overhead, 45M/sec seems reasonable.  Have you look at a running iostat while 
> all this is going on?  Try it out- add up the kb/s from each drive and see 
> how close you are to your maximum theoretical IO.

I didn't try iostat, I did look at vmstat, and there the numbers look even 
worse, the bo column is ~500 for the resync by itself, but with the DD 
it's ~50,000. when I get access to the box again I'll try iostat to get 
more details

> Also, how's your CPU utilization?

~30% of one cpu for the raid 6 thread, ~5% of one cpu for the resync 
thread

David Lang
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