Setting "zfs_arc_max" value in FreeBSD 8.

jhell jhell at
Sat Jan 23 16:19:48 UTC 2010

On Sat, 23 Jan 2010 00:19, fbsdlist@ wrote:
> 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.

Can not wait until I can get something like this spinning!. I'm looking at 
around 6 months before this type of configuration will come into effect 
and be viable. I'm excited!.

> 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

These guys really are doing one hell (maybe 2 or 3 ;]) of a job. Couldn't 
ask for better people to work on this.

> On Fri, Jan 22, 2010 at 6:39 PM, jhell <jhell at> 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
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