If the write-only or read-write cache disks become unavailable because of hardware failure or physical removal from the NAS, all volumes using the write-cache will also become unavailable and will have Cache Missing as their status. QTS restricts access to these volumes to protect data integrity, as some volume data may be stored in the write cache without being flushed to disk.

When the SSD cache is missing, restore it using one of the following methods:

• If the SSD cache disks were removed from the NAS, re-insert the disks into the same drive bays.

• Resolve any RAID errors.

• Restart the NAS.