New ZFSv28 patchset for 8-STABLE

Bob Friesenhahn bfriesen at
Mon Jan 3 21:51:34 UTC 2011

> After four days, the L2 hit rate is still hovering around 10-20 percents (was 
> between 60-90), so I think it's clearly a regression in the ZFSv28 patch...
> And the massive growth in CPU usage can also very nicely be seen...
> I've updated the graphs at (switch time can be checked on the zfs-mem graph):
> There is a new phenomenom: the large IOPS peaks. I use this munin script on a 
> lot of machines and never seen anything like this... I'm not sure whether 
> it's related or not.

It is not so clear that there is a problem.  I am not sure what you 
are using this server for but it is wise to consider that this is the 
funny time when a new year starts, SPAM delivery goes through the 
roof, and employees and customers behave differently.  You chose the 
worst time of the year to implement the change and observe behavior.

CPU use is indeed increased somewhat.  A lower loading of the l2arc is 
not necessarily a problem.  The l2arc is usually bandwidth limited 
compared with main store so if bulk data can not be cached in RAM, 
then it is best left in main store.  A smarter l2arc algorithm could 
put only the data producing the expensive IOPS (the ones requiring a 
seek) in the l2arc, lessening the amount of data cached on the device.

Bob Friesenhahn
bfriesen at,
GraphicsMagick Maintainer,

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