After some recent upgrades:
FreeNAS FreeNAS-9.10.2-U3 (e1497f269)
I noticed myself getting spammed with messages like:
May 4 13:21:42 126.96.36.199 2017-05-04T17:21:42.306Z serverblade1.robpatton.com vmkwarning: cpu0:67660)WARNING: ScsiDeviceIO: 6462: The Physical block size “16384” reported by the device naa.6589cfc0000005aac04099e50185e8c8 is not supported. The only supported physical blocksizes are 512 and 4096
FreeNAS acts as an iSCSI target with its LUNs backed by a ZFS Volume. This causes the blocksize to be reported as the ZFS size, which scares the host, I guess.
To help make the host feel better about itself, login to FREENAS and Sharing > Block (iSCSI) > Extents > Edit > Disable Physical Block Size Reporting
As shown here.
And it should feel better about itself.
For me, this did not work till I rebooted the FREENAS box, which means I had to vmotion all my stuff elsewhere. A fun exercise..