ZFS ARC being limited below what is defined in /boot/loader.conf

Steve Polyack korvus at comcast.net
Fri Feb 12 18:31:13 UTC 2010


Has anyone had an issue with the ZFS ARC max being limited below what 
has been defined in /boot/loader.conf?  I just upgraded the RAM in a 
ZFS-equipped system and attempted to devote 4GB to the ARC cache by 
placing the following in loader.conf:
   vfs.zfs.arc_max="4096M"

However, after rebooting, querying the sysctl gives me this:
$ sysctl vfs.zfs.arc_max
vfs.zfs.arc_max: 1726489600

or about 1.7GB, an odd number that I can't find any references to.  For 
reference, I'm running 8-STABLE (as of Jan 19th) on an amd64 system with 
8GB of RAM.  The system was previously very stable with 4GB of RAM and a 
512MB arc_max.  I have not modified vm.kmem_size_max (defaults to ~330GB 
on amd64) or any other ZFS tunables.  I'd also like to avoid syncing up 
to the current 8-STABLE if at all possible.

Thanks,
Steve Polyack



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