One of your drives (formatted with XFS) has problems. Run a (long) SMART test to see if the drive itself detects an issue (or whether it might be a cable or connection problem). If this is not your Proxmox installation drive, you could check the system logs to maybe get more information on the actual error.
There is no one quick fix depending on the actual error and circumstances. Prepare for replacing the drive and restoring its content from existing backups (as new backups probably fail or will be corrupted).
Its also not specific to Proxmox so other Linux XFS and drive troubleshooting guide will be relevant too.