ZFS, compression, system load, pauses (livelocks?)

[Jonathan]

I seem to have run into the same problem with

"2) long pauses, in what looks like vfs.zfs.txg.timeout second intervals"
http://lists.freebsd.org/pipermail/freebsd-fs/2009-December/007343.html

In my case 50-100% CPU is used by ZFS with *no* disk activity during the 
pauses then a burst of rapid disk activity and then another pause.  I'm 
also not running compression on the file system that I am writing to so 
I don't think it's something specific to compression.

Has anyone had any luck finding a solution or are people still just 
patching around it for now?

I dropped vfs.zfs.txg.timeout from 30 to 5 seconds and my throughput is 
far better, but still sawtoothed.  The actual data transfer "teeth" are 
much closer together but still seem to be spaced at vfs.zfs.txg.timeout 
intervals.  When transferring data I see about 50% of a 1gb link which 
drops to 0 during the pauses.  Based on gstat my disks spend maybe 1/4 
of their time busy so I doubt my array is the limiting factor in this 
situation.

I'm running 8-stable r200414 right now and I don't remember having this 
problem with 8-beta releases so maybe something has changed recently 
that triggered this?

Jonathan Stewart

Sorry for the broken threading.  I've added freebsd-fs to my 
subscription list so I will be able to follow the rest of the discussion 
on the list.