Setting "zfs_arc_max" value in FreeBSD 8.

[Artem Belevich]

Good to hear that it's usable for you even on a relatively low-memory
system. Now, throw in an SSD for L2ARC, more RAM for ARC (and L2ARC
housekeeping) and then it starts to really shine.

As for better than expected performance, in my not-so scientific
benchmarks (copying 10G-large files on 8-disk RAIDZ2 pool until
filesystem is full)  ZFS on FreeBSD did beat the hell out of
OpenSolaris on the same hardware. I was really surprised. I'm sure
something needed to be tuned on OpenSolaris, but it was nice to see
FreeBSD performing so well.

--Artem



On Fri, Jan 22, 2010 at 6:39 PM, jhell <jhell at dataix.net> wrote:
>
> On Fri, 22 Jan 2010 11:47, fbsdlist@ wrote:
>>>>
>>>> Anyone know if it is adjustable on a system with 1024MB of ram ? Is this
>>>> just being auto calculated by some other value ?
>>
>> You may want to make sure that vm.kmem_size is set to a value much
>> larger than vfs.zfs.arc_max. Default value may be too small to allow
>> such a large ARC.
>>
>> On a side note, I'm not sure that ZFS is a good match for system with
>> only 1G of RAM. By trial and error on my box with 8G or memory I've
>> figured out that I need to set arc_max ~1G below physical memory size
>> to avoid lockups under load. YMMV.
>>
>
> ZFS on this box with 1G has been quite enjoyable actually. With the settings
> I have posted I have not had any lockup on stable/7 and no sudden freezes or
> waits for transfers. So this entirely thus far has been a godsend. I had
> even put this thing through some of the tortures that others have posted to
> the list and not come up with the same results but better. There is
> obviously a lot of variables in this between hardware and configurations
> used so the results are minimal in comparison. With ZFS in place on this
> machine it performs a little bit under specs for the hardware but I wouldn't
> expect anything less for such a file-system.
>
> --
>
>  Thoughts & Prayers out to Haiti.
>
>  jhell
>
>