On Wed, May 16, 2012 at 3:35 PM, Paynter, Richard
<richard.payn...@infocrossing.com> wrote:

> Does anyone know what the minimum value for zfs_arc_max should be set to?
> Does it depend on the amount of memory on the system, and – if so – is there
> a formula, or percentage, to use to determine what the minimum value is?

    I would assume that it should not be set any lower than `kstat
zfs::arcstats:c_min`, which I assume you can set with zfs_arc_min in
/etc/system, but that does not really answer your question. Under
Solaris 10 I have set it as low as 1 GB with no (apparent) ill effects
except the desired reduction in the ARC and performance associated
with such. This was NOT for production, but purely testing.

    Why are you trying to tune the ARC as _low_ as possible? In my
experience the ARC gives up memory readily for other uses. The only
place I _had_ to tune the ARC in production was a  couple systems
running an app that checks for free memory _before_ trying to allocate
it. If the ARC has all but 1 GB in use, the app (which is looking for
about 2.5 GB) does not see enough free memory and tosses an out of
memory error without even trying to actually get the memory it needs.
I have the ARC max tuned to 4 GB on these boxes with 16 GB RAM.
Instead of my ARC using 10-12 GB it is stuck with only 4 GB, but the
application does not quite with an error. Yes, I have flagged this
behavior for the vendor, they don't seem to care.

Paul Kraus
-> Senior Systems Architect, Garnet River ( http://www.garnetriver.com/ )
-> Assistant Technical Director, LoneStarCon 3 (http://lonestarcon3.org/)
-> Sound Coordinator, Schenectady Light Opera Company (
http://www.sloctheater.org/ )
-> Technical Advisor, Troy Civic Theatre Company
-> Technical Advisor, RPI Players
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