ZFS: Disabling ARC?

PK1048 info at pk1048.com
Mon Aug 3 13:50:05 UTC 2015


Sent from my portable device

On Aug 3, 2015, at 03:04, Quartz <quartz at sneakertech.com> 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?

I expect that ZFS would be functionally useless (from a performance standpoint) 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_Tuning_Guide before doing any ZFS tuning. It was written in the early (Solaris only) 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/blogs/brendan/2012/01/09/activity-of-the-zfs-arc/ I suspect that will answer most of your ARC questions in detail.



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