Setting "zfs_arc_max" value in FreeBSD 8.

[jhell]

On Sat, 23 Jan 2010 04:25, Alexander@ wrote:
> On Fri, 22 Jan 2010 21:39:48 -0500 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.
>
> You may want to switch to fletcher4 checksums. This is the default in
> Solaris and 8.0 now. I didn't merge this change to 7-stable as I didn't
> took the time to analyze if the change for the default has some unwanted
> implications for existig pools.
>

I will do this and report back with any differences that I find. As for 
your previous email that arrived I believe after this one, Thank you for 
your replies I appreciate the feedback.

> I have a 9-current box with 1GB RAM and ZFS which shows the slow-down
> after some hours of running (and doing things) too. It would be good to
> make a list of OS versions and if there are slowdowns or not (anyone
> with time out there to have a look at the mails and get this info out
> of the mails / people?). Maybe it is related to changes not in ZFS...
>
> Bye,
> Alexander.
>

Is there any recommendations from anyone ? so there is a basis for what 
can be tested from. (unixbench|iozone|others) in comparison to the same 
results version to version ?

Thanks

-- 

  jhell