Ceph » rbd

Hi guys,
I'm testing rbd backup with Veritas NetBackup，here is the steps blow:
1.Create rbd in ceph
[root @node1] rbd creates a test-backup/rbd-1 --size 100MB --image-feature layering
2.rbd diff test-backup/rbd-1 | awk'{SUM += $2} END {print SUM}'
result is 0
2.rbd mapping rbd-1
[root @node1] rbd mapping test-backup/rbd-1
/dev/rbd0
3.backup and restore /dev/rbd0 on node1
Use veritas netbackup to backup and restore the rbd block device /dev/rbd0 created by ceph. The backup will back up all the block devices including file system partitions and unwritten data, and restore the same process
5.unmap rbd
6.rbd diff test-backup/rbd-1 | awk'{SUM += $2} END {print SUM}'
result is 100

I want to solve the problem of 100% usage after restore，thanks！