Date: Mon, 3 Aug 2015 08:18:00 -0400 From: PK1048 <info@pk1048.com> To: FreeBSD Filesystems <freebsd-fs@freebsd.org> Subject: Re: ZFS: Disabling ARC? Message-ID: <12AA569B-829F-418F-B7B4-897F34B92067@pk1048.com> 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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Sent from my portable device On Aug 3, 2015, at 03:04, Quartz <quartz@sneakertech.com> wrote: >> If you are really worried about the ARC hogging RAM, then set a cap. >> The kernel tunables here are: >=20 > I'm not worried about it hogging ram per se, but rather I'm a little confu= sed about where and when it helps, where it's useless or detrimental (if eve= r), and consequently I don't really know when I should tune it or what to tu= ne 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 lo= ok like? I expect that ZFS would be functionally useless (from a performance standpoi= nt) if you completely disabled the ARC, I'm not even sure you can. Take a look at http://www.solarisinternals.com/wiki/index.php/ZFS_Evil_Tunin= g_Guide before doing any ZFS tuning. It was written in the early (Solaris on= ly) days of ZFS, but is still for the most part applicable today. Brendan Gregg has a very good blog entry on the ARC here http://dtrace.org/b= logs/brendan/2012/01/09/activity-of-the-zfs-arc/ I suspect that will answer m= ost of your ARC questions in detail.
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