Unfortunately yes, even VM's/disks on the NFS data domain are giving the same error. Just to be sure, i just created a completely new NFS data share on Truenas imported the data domain to ovirt and created a new test vm with 2 thin provisioned disks on it, cannot sparsify neither: "Error while executing action: Cannot sparsify Virtual Disk. Sparsifying is not supported for QCOW2 disk testvm3_Disk1." I checked the NFS share on Truenas to make sure i have a sparse qcow2 file and it is: -rw-rw---- 1 vdsm ovirt-kvm 24G Jan 12 12:57 a0f82c8b-d2aa-442b-b28b-b25ca684dd7b -rw-rw---- 1 vdsm ovirt-kvm 1.0M Jan 12 12:44 a0f82c8b-d2aa-442b-b28b-b25ca684dd7b.lease -rw-r--r-- 1 vdsm ovirt-kvm 307 Jan 12 12:44 a0f82c8b-d2aa-442b-b28b-b25ca684dd7b.meta root@truenas[.../29dcdef7-8d1d-48bc-b9cf-3850102ec251]# file a0f82c8b-d2aa-442b-b28b-b25ca684dd7b a0f82c8b-d2aa-442b-b28b-b25ca684dd7b: QEMU QCOW2 Image (v3), 26843545600 bytes