I think I know why was the server misbehaving. One of boot SSDs is failing.
SMART overall-health self-assessment test result: FAILED!
Drive failure expected in less than 24 hours. SAVE ALL DATA.
No failed Attributes found.
@caskd I think you need to add the drive to the array
@matrix https://raid.wiki.kernel.org/index.php/Replacing_a_failed_drive
assuming you're using mdadm
@matrix
NO!
You need to at least add the new disk to the array.
If you are booting from a Linux RAID1 array, can you just power it off, replace the drive and it boots up and starts rebuilding?