Just finished recovering a Nexenta 2011 system. The underlying faults were hba/cable/backplane/drives/no usable os. On just out of production hardware (Ibex Peak) running a functioning, licensed, Nexenta os, the pools imported without issue. An Hitachi SAS pool resilvered, all online, a Constellation SATA pool remained degraded, a faulty drive was removed, errors remained, a drive was going offline. Replaced Nexenta with 11.2-U7, moved degraded Constellation pool to the Hitachi backplane, pool remained degraded but drives stayed online. Replicated to new pools, zfs set readonly=off. Thanks everyone for your help.
A correction on the drives:
The Hitachi pool are sata not sas, now no errors reported.
The degraded pool was Seagate NAS, not Constellation, now no errors reported, the failed drive a Barracuda spare.
Also failed, an Intel SSD 320 Series 80GB.
An update on the Seagate pool:
One of the Seagate NAS drives fails SMART, short drive self test at 10%, long generic test at 24%.
19,713 hours ~ 2.25 years.
Seagate warranty expired 2016, drive reported as IronWolf.
