failed drive?

[Chris Murphy]

The drive is failing. Reallocated sectors is so high that they're are almost no reserve sectors remaining at which point any additional bad sectors well result in write failure. So in any case it needs to be replaced.

The array it's in is an Intel firmware RAID, sometimes annoyingly called "fake RAID" so it might be going inactive due to some firmware policy in order to get the users attention? But  ultimately under Linux is managed by the Linux MD driver and mdadm. Usually these are boot volumes or Windows volumes. Otherwise you'd just set it up with mdadm superblock/metadata like the others.