current zfs tuning in RELENG_7 (AMD64) suggestions ?

[Pete French]

> In the past it had been suggested that for zfs tuning, something like
>
> vm.kmem_size_max="1073741824"
> vm.kmem_size="1073741824"
> vfs.zfs.prefetch_disable=1
>
> However doing a simple test with bonnie and dd, there does not seem 
> to be very much difference in 4 configs.  Am I better off just with 

The tuning isn't there to improve performance, it's there to prevent
the box going titus due to a panic when the ARC gets too big, and
you are missing the mian one, which is to limit the size of the ARC.
On recent versions of BSD (and you are running 7.2, so thats fine) then
the defaults for kmem size are fine, but you still need something like this:

vfs.zfs.arc_max="256M"

In there to stop the ARC growing. thats the only tuning I have on
my 4 gig machine, which takes a steady stream of data and is used
for taking backup snapshots. ZFS is excellent, and for me is perfectly
stable, to the point where I am starting to roll it out to production
machines, with the above tuning.

-pete.