I have a customer who wants to set zfs_arc_max to 1G for a 16G system,
and 2G for a 32G system.  Both of these are SAP and/or Oracle db
servers.  They apparently want to maximize the amount of memory
available for the applications.


My question, now, is whether it would be advisable to do this, and - if
not - what the impact might be.


The 32G system is an M3000; the 16G system is a V490.  Both are running
Solaris 10 Update 8, patched to 147440-09.


I have a feeling that setting zfs_arc_max this low is not a good idea,
but would like to get some corroborating information/references, if






From: zfs-discuss-boun...@opensolaris.org
[mailto:zfs-discuss-boun...@opensolaris.org] On Behalf Of Richard Elling
Sent: Thursday, May 17, 2012 11:24 AM
To: Paul Kraus
Cc: ZFS Discussions
Subject: Re: [zfs-discuss] zfs_arc_max values


On May 17, 2012, at 5:28 AM, Paul Kraus wrote:

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

        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. 


arc_c_max and arc_c_min are used for different things. If you make

changes there, then it is a good idea to set both zfs_arc_min,
zfs_arc_max, and

zfs_arc_meta_limit as a set.


NB, the minimum size of these is 64MB.

 -- richard



ZFS Performance and Training








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