We have this error on an MD3820f: "MD3820f Cache Backup Device Failed"

and in the log:

ERROR: checkBackupSpaceAvailability: checkBackupCapacity for ALT_CB_VOL failed

WARN: CCM: checkSpaceAvailability() Insufficient backup storage

What in https://www.dell.com/community/en/conversations/powervault/md3820f-cache-backup-device-failed/64c10602f4ccf8a8ded024bb doesn't work.

We don't want to buy a new controller for expensive money.