Dangling Device Mappers Found

Issue

I cannot clean the Dangling Device Mappers.

Environment

OnApp 3.x, 4.x, 5.x, 6.x

Integrated Storage

Resolution

If the disk belongs to an online virtual machine, then rebooting the virtual machine should fix the issue. You can find which virtual machine uses that disk by following this article.

If the VM is offline, then the entries are on one of the HVs. They can be found with dmsetup ls --tree | grep <<disk_id>> and removed using dmsetup remove

Example:

[root@11.12.13.14 ~]# dmsetup ls --tree | grep asdfasdfasdf12
 asdfasdfasdf12 (253:8)
 |-3_asdfasdfasdf12 (253:7)
 |-2_asdfasdfasdf12 (253:6)
 |-1_asdfasdfasdf12 (253:5)
 `-0_asdfasdfasdf12 (253:4)
 [root@11.12.13.14 ~]# dmsetup remove asdfasdfasdf12
 [root@11.12.13.14 ~]# dmsetup remove 0_asdfasdfasdf12
 [root@11.12.13.14 ~]# dmsetup remove 1_asdfasdfasdf12
 [root@11.12.13.14 ~]# dmsetup remove 2_asdfasdfasdf12
 [root@11.12.13.14 ~]# dmsetup remove 3_asdfasdfasdf12
 [root@11.12.13.14 ~]#

Additional Info

'Dangling device mapper' indicates that there is some orphaned connections on the HV for a VM disk. These would not usually cause data loss, but they can interfere with transactions and backups as the storage may have issues activating or deactivating a given disk.