TL;DR

Solaris 11.4 SRU 90 now does resilvering and scrubbing, while freeing space is pending.

Closing a time gap

Oracle Solaris had reached ZFS pool version 53 so far. With SRU 90, version 54 was added. This becomes visible in the version overview:

root@testbed:~# zpool upgrade -v
This system is currently running ZFS pool version 54.
The following versions are supported:
VER  DESCRIPTION
---  --------------------------------------------------------
  1  Initial ZFS version
  [...]
 54  Scan with pending free
 
For more information on a particular version, including supported releases, see the ZFS Administration Guide.

When performing operations in ZFS, some tasks are carried out in the background — for example, the freeing of blocks that were previously used by deleted snapshots or clones. For larger operations, this can take hours or even days.

Until now, scrubs or resilverings were not performed during this time and had to wait until the freeing process was complete. Especially the postponement of resilvering could be problematic. Pool version 54 closes this gap and allows a “scan with pending free.”

The upgrade is very straightforward:

root@testbed:~# zpool upgrade test   
This system is currently running ZFS pool version 54.
Successfully upgraded 'test' from version 53 to version 54

However, the usual caveat applies: only perform the upgrade once you are certain that you no longer want to roll back to an older version of Solaris 11.4.¹ An older version may not be able to mount a pool with a higher ZFS pool version.

Or rather, once you are certain that the version you might want to roll back to also supports the new pool version. However, with SRU 90 and ZFS pool version 54, there is no older SRU supporting version 54. ↩