Comment 1 for bug 1809241

This happens because BlockDevice has a unique_together on (node,name).

In this case the name would be the same, but since these are two VirtualBlockDevices with a different filesystem_group it's actually ok.

I think we need to drop the unique index and add an explicit check in BlockDevice.save() for it, and override it in VirtualBlockDevice.save() so that it takes into account the filesystem_group as well.