ZFS vs OSX Time Machine

[Artem Belevich]

On Thu, Apr 28, 2011 at 6:08 PM, Jeremy Chadwick
<freebsd at jdc.parodius.com> wrote:
> I will note something, however: your ARC max is set to 3072MB, yet Wired
> is around 4143MB.  Do you have something running on this box that takes
> up a lot of RAM?  mysqld, etc..?  I'm trying to account for the "extra
> gigabyte" in Wired.  "top -o res" might help here, but we'd need to see
> the process list.
>
> I'm thinking something else on your machine is also taking up Wired,
> because your arcstats shows:
>
>> kstat.zfs.misc.arcstats.c: 3221225472
>> kstat.zfs.misc.arcstats.c_min: 402653184
>> kstat.zfs.misc.arcstats.c_max: 3221225472
>> kstat.zfs.misc.arcstats.size: 3221162968
>
> Which is about 3072MB (there is always some degree of variance).

The difference is probably due to fragmentation (most of ARC
allocations are served from power-of-2 zones, if I'm not mistaken) + a
lot of wired memory sits in slab allocator caches (FREE column in
vmstat -z). On a system with ARC size of ~16G I regularly see ~22GB
wired. Ona smaller box I get about 7GB wired at around 5.5GB ARC size.

--Artem