On Fri, 2005-05-06 at 22:16, John David Duncan wrote:
> > And no performance diff. Note that you're benchmarks only show a 20M
> > addition overhead. We're about 60x too slow for these drives so I'm
> > not
> > sure what could be going on here :-/
> I know of a site that encountered a similar performance issue:
> The OS was reading in a lot more data from the disk than the
> database really needed.
> The culprit turned out to be the stripe size on a 4-disk RAID.
> By reducing the stripe size from 768K to 32K, they obtained a
> 200% increase in mysql throughput.
This is actually interesting point, as we typically recommend large
stripes with MySQL (RAID 10 best)
This may sounds like contradiction but it is not. You need to have
large stripe set (256-1024K+) but small RAID controller cache line
(16K for Innodb tables)
The thing is by default many RAID controllers would put cacheline size
= stripe size, some may not even allow to change it.
If it is the case MySQL will have to read a lot of unnecessary data
which will kill performance.
Peter Zaitsev, Senior Performance Engineer
Come to hear my talk at MySQL UC 2005 http://www.mysqluc.com/
MySQL AB, www.mysql.com