[LU-4277] Integrate ZFS zpool resilver status with OFD OS_STATE_DEGRADED flag

• Type: Improvement
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.11.0
• Affects Version/s: Lustre 2.11.0
• Labels: zfs
• Assignee: Nathaniel Clark
• Reporter: Andreas Dilger

Description

The OFD statfs() handled can optionally add an OS_STATE_DEGRADED flag to the statfs reply, which the MDS uses to help decide which OSTs to allocate new file objects from. Unless all other OSTs are also degraded, offline, or full, the DEGRADED OSTs will be skipped for newly created files.

This avoids the application waiting for slow writes because of the rebuild long after it has completed on other healthy OSTs. It also avoids the new writes from interfering with the OST rebuild process, so it is a double win.

This was previously implemented as a /proc tunable suitable for mdadm or a hardware-RAID utility to set from userspace, but since ZFS RAID is in the kernel it should be possible to query this status directly from the kernel when the MDS statfs() arrives.

Issue Links

• is related to: LU-6767 Capture READONLY status in osd-zfs osd_statfs()