Understanding background disk firmware updates
When a node reboots and there is new disk firmware present, the affected drives are automatically and sequentially taken offline, and the node responds normally to read and write requests.
If any request affects an offline drive, the read requests are satisfied by reconstructing data from other disks in the RAID group, while write requests are written to a log. When the disk firmware update is complete, the drive is brought back online after resynchronizing any write operations that took place while the drive was offline.
During a background disk firmware update, the node functions normally. You see status messages as disks are taken offline to update firmware and brought back online when the firmware update is complete. Background disk firmware updates proceed sequentially for active data disks and for spare disks. Sequential disk firmware updates ensure that there is no data loss through double-disk failure.
Offline drives are marked with the annotation offline in the nodeshell vol status -r command output. While a spare disk is offline, it cannot be added to a volume or selected as a replacement drive for reconstruction operations. However, a disk would normally remain offline for a very short time (a few minutes at most) and therefore would not interfere with normal cluster operation.
The background disk firmware update is completed unless the following conditions are encountered:
Degraded aggregates are on the node.
Disks needing a firmware update are present in an aggregate or plex that is in an offline state.
Automatic background disk firmware updates resume when these conditions are addressed.