ZFS vdev I/O questions

[Mark Felder]

On Tue, Jul 16, 2013, at 8:16, Daniel Kalchev wrote:
> 
> Could this be DDT/metadata specific issue? Is the DDT/metadata 
> vdev-specific? The pool initially had only two vdevs and after vdev 3 
> was added, most of the written data had no dedup enabled. Also, the ZIL 
> was added later and initial metadata could be fragmented. But.. why 
> should this affect writing? The zpool is indeed pretty full, but 
> performance should degrade for all vdevs (which are more or less equally 
> full).
> 

I don't want to put you down the wrong path, but you're right -- the
zpool is pretty full, and zfs is known to have issues writing when above
~80%. There's another thread where this was discussed briefly. However,
you have quite a large pool so I find it hard to believe that your
3.45TB free is so fragmented that zfs is having issues choosing where to
write. It's certainly possible, though. 

Hopefully someone will drop in their 2c as well