Writing halted on iSCSI zpool

I am running 9.2.1.8 Release x64 with 6x3TB drives in a raidz2 pool. I setup an iscsi target that allocates all but 800k of the zfs pool. This config has been running fine for about a year. Now, I am getting alerts that the capacity of my pool is at 98%. The pool is 10.3TB and ~5TB are in use via a Windows box through the iscsi. At this point, I cannot write anything to the drive via Windows due to an I/O error. The freenas box is incredibly slow. It is also running a scrub at the...

Writing halted on iSCSI zpool