Spares low checking is triggered under the following conditions:
- At boot and takeover time.
- By hourly check of spares by global status monitor.
- When the M-host or a management applications invokes the aggr-check-spares-low Zapi.
- When configuration change may result in new demand for spares, such as when an aggregate or plex is onlined.
- Anytime the population of a spare pool changes.
There are two cases for change to population of a spare pool, addition and subtraction.
- Addition: This includes the following cases:
- Spare disks are added and/or assigned to a system. This includes case where disk is dynamically qualified, or finally completes initialization after initial failure.
- An aggregate or plex is offlined and destroyed and its disks released to the spare pool.
- Aggregate orphan disks are released to the spare pool.
- A disk in broken pool is unfailed.
- A disk is released from disk maintenance center with no trouble found.
- Demotion of aggregate or RAID group type from RAID-DP to RAID4.
- Subtraction: This includes the following cases:
- Aggregate or plex creation.
- Promotion of unmirrored to mirrored aggregate.
- Addition of disks to an existing aggregate.
- Promotion of aggregate or RAID group type from RAID4 to RAID-DP.
- Allocation of replacement disk for reconstruction, disk copy operation for sick disk, disk replacement, or Boab carrier evacuation.
- A spare disk is removed or failed.
- A spare disk gets placed into disk maintenance center. This includes for maintenance testing, disk sanitization and disk recovery.