New ZFSv28 patchset for 8-STABLE

[Attila Nagy]

  On 12/16/2010 01:44 PM, Martin Matuska wrote:
> Link to the patch:
>
> http://people.freebsd.org/~mm/patches/zfs/v28/stable-8-zfsv28-20101215.patch.xz
>
>
I've used this:
http://people.freebsd.org/~mm/patches/zfs/v28/stable-8-zfsv28-20101223-nopython.patch.xz
on a server with amd64, 8 G RAM, acting as a file server on 
ftp/http/rsync, the content being read only mounted with nullfs in 
jails, and the daemons use sendfile (ftp and http).

The effects can be seen here:
http://people.fsn.hu/~bra/freebsd/20110101-zfsv28-fbsd/
the exact moment of the switch can be seen on zfs_mem-week.png, where 
the L2 ARC has been discarded.

What I see:
- increased CPU load
- decreased L2 ARC hit rate, decreased SSD (ad[46]), therefore increased 
hard disk load (IOPS graph)

Maybe I could accept the higher system load as normal, because there 
were a lot of things changed between v15 and v28 (but I was hoping if I 
use the same feature set, it will require less CPU), but dropping the 
L2ARC hit rate so radically seems to be a major issue somewhere.
As you can see from the memory stats, I have enough kernel memory to 
hold the L2 headers, so the L2 devices got filled up to their maximum 
capacity.

Any ideas on what could cause these? I haven't upgraded the pool version 
and nothing was changed in the pool or in the file system.

Thanks,