What we see in the data you sent: Qemu chain: $ qemu-img info --backing-chain /dev/33777993-a3a5-4aad-a24c-dfe5e473faca/6197b30d-0732-4cc7-aef0-12f9f6e9565b image: /dev/33777993-a3a5-4aad-a24c-dfe5e473faca/6197b30d-0732-4cc7-aef0-12f9f6e9565b file format: qcow2 virtual size: 150G (161061273600 bytes) disk size: 0 cluster_size: 65536 backing file: 8e412b5a-85ec-4c53-a5b8-dfb4d6d987b8 (actual path: /dev/33777993-a3a5-4aad-a24c-dfe5e473faca/8e412b5a-85ec-4c53-a5b8-dfb4d6d987b8) backing file format: qcow2 Format specific information: compat: 1.1 lazy refcounts: false refcount bits: 16 corrupt: false image: /dev/33777993-a3a5-4aad-a24c-dfe5e473faca/8e412b5a-85ec-4c53-a5b8-dfb4d6d987b8 file format: qcow2 virtual size: 150G (161061273600 bytes) disk size: 0 cluster_size: 65536 Format specific information: compat: 1.1 lazy refcounts: false refcount bits: 16 corrupt: false Vdsm chain: $ cat 6197b30d-0732-4cc7-aef0-12f9f6e9565b.meta CAP=161061273600 CTIME=1594060718 DESCRIPTION= DISKTYPE=DATA DOMAIN=33777993-a3a5-4aad-a24c-dfe5e473faca FORMAT=COW GEN=0 IMAGE=d7bd480d-2c51-4141-a386-113abf75219e LEGALITY=ILLEGAL ^^^^^^ This is the issue, the top volume is illegal. PUUID=8e412b5a-85ec-4c53-a5b8-dfb4d6d987b8 TYPE=SPARSE VOLTYPE=LEAF $ cat 8e412b5a-85ec-4c53-a5b8-dfb4d6d987b8.meta CAP=161061273600 CTIME=1587646763 DESCRIPTION={"DiskAlias":"cpslpd01_Disk1","DiskDescription":"SAP SLCM H11 HDB D13"} DISKTYPE=DATA DOMAIN=33777993-a3a5-4aad-a24c-dfe5e473faca FORMAT=COW GEN=0 IMAGE=d7bd480d-2c51-4141-a386-113abf75219e LEGALITY=LEGAL PUUID=00000000-0000-0000-0000-000000000000 TYPE=SPARSE VOLTYPE=INTERNAL We set volume to ILLEGAL when we merge the top volume into the parent volume, and both volumes contain the same data. After we mark the volume as ILLEGAL, we pivot to the parent volume (8e412b5a-85ec-4c53-a5b8-dfb4d6d987b8). If the pivot was successful, the parent volume may have new data, and starting the vm using the top volume may corrupt the vm filesystem. The ILLEGAL state prevent this. If the pivot was not successful, the vm must be started using the top volume, but it will always fail if the volume is ILLEGAL. If the volume is ILLEGAL, trying to merge again when the VM is not running will always fail, since vdsm does not if the pivot succeeded or not, and cannot merge the volume in a safe way. Do you have the vdsm from all merge attempts on this disk? The most important log is the one showing the original merge. If the merge succeeded, we should see a log showing the new libvirt chain, which should contain only the parent volume. Nir