I've recently converted 8x6TB disks into 4 mirrored vdev's to play with ZFS (1.6.1). The performance is much less than expected, particularly with writes--like, 40-50MB/s. That's much less than the speed of a single disk, so something seems odd. No compression or dedup enabled, default 128k record size. I'm on an iMac using 2x Thunderbolt enclosures that were previously doing work w/ SoftRAID.
Before I just spray a fire hose of output - is there any particular command(s) that would be helpful?