dm-ioctl - DM_TABLE_STATUS

Returns status information from each of the mappings in the table. For example, for mirroring, this tells you what percentage of the mirror is in-sync. For snapshots, it says how full the snapshot is. For multipath it tells you which paths have failed and which path group is currently being used.
If DM_STATUS_TABLE_FLAG is set, instead of the mapping status it returns a copy of the Active table.

Returns status information from each of the mappings in the table. For example, for mirroring, this tells you what percentage of the mirror is in-sync. For snapshots, it says how full the snapshot is. For multipath it tells you which paths have failed and which path group is currently being used.