Are any adjustments for ZFS necessary in 8.1 amd64?

[Torbjorn Kristoffersen]

On Wed, Oct 6, 2010 at 5:15 AM, jhell <jhell at dataix.net> wrote:
> On 10/05/2010 20:50, Trever wrote:
>> Apologies if this has been answered previously, but I can't find definitive info.
>>
>> The FBSD handbook recommends a customized loader.conf when using ZFS (for all architectures):
>> vm.kmem_size="330M"
>> vm.kmem_size_max="330M"
>> vfs.zfs.arc_max="40M"
>> vfs.zfs.vdev.cache.size="5M"
>>
>> Is this still true for the 8.1 amd64 release?  I've read various places that it is not and that handbook is NOT up-to-date.  Out of the box, amd64 8.1 ZFS so far "just works" without any customizations other than to make sure it turns on at reboot.  But systems are fairly quiescent, we have not gone to production yet.
>>
>> In addition to the handbook recommendations, are there 8.1 amd64 tunings that should be done for a vanilla server?  (Will be imap server, actually.)
>>
>> Without tuning as per above, I see this on our systems (sysctl -a):
>> vm.kmem_size: 8318648320
>> vm.kmem_size_max: 329853485875
>> vfs.zfs.arc_max: 7244906496
>> vfs.zfs.vdev.cache.size: 10485760
>>
>> Our systems have 24 GB of RAM.
>>
>
> With the amount of RAM that you have available in your system I would
> not recommend using the above values that you quoted from the Wiki.
> Those values from the wiki IIRC were based on a i386 system that has
> less than 1G of RAM and were used as an example more than a definitive
> tuning to achieve better performance.
>
> With all the available configurations that are possible with a ZFS based
> FreeBSD system I would suggest that you try out the defaults and move
> from that point onward before you try tuning for a specific scenario. It
> will be best to have a definitive starting point at which you can always
> refer back to in your performance testing.
>

I've got the same setup except 8GB of memory.  I'd also like to tune
as best as I can, but I'm uncertain of how far I should try to go.
It's a production system so I'm playing it a bit careful. Using
default settings now, but I'm also interested in better performance.

TK