QCOW or IMG

[mikeyosm]

Hi

 

I am converting my vmware vmdks ready for UNRAID. Should I convert them to .QCOW2 or .IMG format? Which is better and for what reasons? Thanks.

[itimpi]

qcow2 allocates space dynamically as required so typically uses less space.  It also in theory supports snapshotting for VMs although unRAID does not currently make use of this feature.

 

img allocates all the space up front (although on unRAID it can make use of sparse files to mean on-disk space is less than might be expected\).  It normally gives better performance than .qcow2

[mikeyosm]

qcow2 allocates space dynamically as required so typically uses less space.  It also in theory supports snapshotting for VMs although unRAID does not currently make use of this feature.

 

img allocates all the space up front (although on unRAID it can make use of sparse files to mean on-disk space is less than might be expected\).  It normally gives better performance than .qcow2

 

I guess by 'normally better' this implies a static file that never grows/shrinks so no fragmentation? I suppose this is the 'thick' provisioning that vmare uses.