Date: Mon, 3 Aug 2015 08:31:46 -0500 (CDT) From: Bob Friesenhahn <bfriesen@simple.dallas.tx.us> To: Quartz <quartz@sneakertech.com> Cc: freebsd-fs@freebsd.org Subject: Re: ZFS: Disabling ARC? Message-ID: <alpine.GSO.2.01.1508030826020.4186@freddy.simplesystems.org> In-Reply-To: <55BF1270.10003@sneakertech.com> References: <55BC14B7.9010009@sneakertech.com> <9DBE58C6-8C42-498B-AB66-7D9BBDFAA90F@kraus-haus.org> <55BF1270.10003@sneakertech.com>
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On Mon, 3 Aug 2015, Quartz wrote: >> If you are really worried about the ARC hogging RAM, then set a cap. >> The kernel tunables here are: > > I'm not worried about it hogging ram per se, but rather I'm a little confused > about where and when it helps, where it's useless or detrimental (if ever), > and consequently I don't really know when I should tune it or what to tune it > *to*. > > Basically, my question is the subject line of this thread: is there ever a > reason to attempt to disable ARC, and what would that situation probably look > like? ARC is intrinsic to the design of zfs and so it can not be entirely disabled. Without caching, zfs would perform terribly, and some caching is needed in order for transaction groups to work. The types of data (data/metadata) cached in the ARC are tunable on a filesystem basis. If you do not encounter a problem, then you should not worry about it. The whole point of the ARC algorithm is that it self-tunes itself to meet available resources and requirements. Bob -- Bob Friesenhahn bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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