New ZFSv28 patchset for 8-STABLE

Pawel Jakub Dawidek pjd at
Mon Jan 10 09:14:30 UTC 2011

On Sun, Jan 09, 2011 at 12:52:56PM +0100, Attila Nagy wrote:
> I've finally found the time to read the v28 patch and figured out the 
> problem: vfs.zfs.l2arc_noprefetch was changed to 1, so it doesn't use 
> the prefetched data on the L2ARC devices.
> This is a major hit in my case. Enabling this again restored the 
> previous hit rates and lowered the load on the hard disks significantly.

Well, not storing prefetched data on L2ARC vdevs is the default is
Solaris. For some reason it was changed by kmacy@ in r205231. Not sure
why and we can't ask him now, I'm afraid. I just sent an e-mail to
Brendan Gregg from Oracle who originally implemented L2ARC in ZFS why
this is turned off by default. Once I get answer we can think about
turning it on again.

Pawel Jakub Dawidek             
pjd at                 
FreeBSD committer                         Am I Evil? Yes, I Am!
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