Re: limits on raid

On Mon, 18 Jun 2007, Brendan Conoboy wrote:

david@lang.hm wrote:

quoted

 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