On MooseFS 4.57.5, when mfsbdev map is followed by mount operation in shell script, mount command fails because block device is not yet ready right after mfsbdev map reported that block device is started:

started block device: (/dev/mfs/extracted_raw->/dev/nbd0 : MFS:/r6/ec41/extracted.btrfs : 8192.000GiB)

mount: /mnt/{{mount_path}}: wrong fs type, bad option, bad superblock on /dev/nbd0, missing codepage or helper program, or other error.
       dmesg(1) may have more information after failed mount system call.

As workaround I had to insert sleep 8 after mfsbdev map and before mount to give block device time to initialise.