There are many important issues to consider when performing a background disk firmware update.
When a storage system configured with RAID-DP or SyncMirror reboots and there is a new disk firmware present, the affected drives are automatically and sequentially taken offline, and the storage system 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 storage system functions normally. You will 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 will be no data loss through double-disk failure.
Offline drives are marked with the annotation "offline" in the 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 system operation.
Automatic background disk firmware updates will resume when these conditions are addressed. For more information about determining volume status and state, see the Data ONTAP Storage Management Guide.
Automatic background disk firmware updates are overridden when the disk_fw_update command is issued.