ZFS Tuning - arc_summary.pl

Ben Kelly ben at wanderview.com
Mon Mar 29 16:28:05 UTC 2010

On Mar 29, 2010, at 10:43 AM, Barry Pederson wrote:

> I've been using the arc_summary.pl script from here:
> http://jhell.googlecode.com/svn/base/head/scripts/zfs/arc_summary/arc_summary.pl
> and noticed some odd numbers, with the ARC Current Size being larger than the Max Size, and the breakdown adding up to less than the current size as shown below

I believe the current size can be larger than the max if your working data set is large enough.  The ARC can't evict data that is still being referenced.  When I last looked (over a year ago) there was no mechanism to provide back pressure from the ARC to the VM layer to request that more nodes be released to help deal with this situation.

I don't know if that really helps at all, but I just thought I would add the data point from my previous debugging sessions with zfs.

- Ben

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