UNS: Re: ZfS & GEOM with many odd drive sizes

[Doug Rabson]

On Thursday 19 July 2007, Mark Powell wrote:
> On Thu, 19 Jul 2007, Doug Rabson wrote:
> > On Thursday 19 July 2007, Mark Powell wrote:
> >> Should I expect much greater CPU usage with ZFS?
> >>    I previously had a geom raid5 array which barely broke a sweat
> >> on benchmarks i.e simple large dd read and writes. With ZFS on the
> >> same hardware I notice 50-60% system CPU usage is usual during
> >> such tests. Before the network was a bottleneck, but now it's the
> >> zfs array. I expected it would have to do a bit more 'thinking',
> >> but is such a dramatic increase normal?
> >>
> >>    Many thanks again.
> >
> > ZFS does a checksum on every block it reads from the disk which may
> > be your problem. In normal usage, this isn't a big deal due because
> > many reads get data from the cache.
>
> I've turned off checksums, but still my machine is struggling. I
> think my Athlon XP is a little old for all this work :( Any other
> tips for speeding zfs up?
>    Cheers.

Nothing really comes to mind. You could try simpler geometries (e.g. 
mirrors or collections of mirrors). Having at least some of your drives 
in a simple configuration might be useful - I'm working on ZFS boot 
code at the moment and I don't intend to support raidz or raidz2 (at 
least to start with). Collections of mirrors and simple disks are much 
easier.