Trying to use mdadm to grow a raid5 array from 2 to 4 devices, I started it with the --backup-file argument to ensure integrity. This seems to have caused mdadm-grow-continue@...service to have failed: ● mdadm-grow-continue@md123.service - Manage MD Reshape on /dev/md123 Loaded: loaded (/lib/systemd/system/mdadm-grow-continue@.service; static; vendor preset: enabled) Active: failed (Result: exit-code) since Sun 2017-12-17 16:20:11 EST; 19h ago Main PID: 10875 (code=exited, status=2) Dec 17 16:20:10 hostname.fqdn systemd[1]: Started Manage MD Reshape on /dev/md123. Dec 17 16:20:11 hostname.fqdn systemd[1]: mdadm-grow-continue@md123.service: Main process exited, code=exited, status=2/INVALIDARGUMENT Dec 17 16:20:11 hostname.fqdn systemd[1]: mdadm-grow-continue@md123.service: Unit entered failed state. Dec 17 16:20:11 hostname.fqdn systemd[1]: mdadm-grow-continue@md123.service: Failed with result 'exit-code'. And the grow seemed to freeze at having reshaped a single block. Manually running mdadm --grow --continue /dev/md123 --backup-file ... got things running again.