--- QemuServer.orig.pm	2019-02-01 13:04:19.000000000 +0100
+++ QemuServer.patched.pm	2019-02-12 16:47:56.000000000 +0100
@@ -6461,6 +6461,46 @@
 	my $src_path = PVE::Storage::path($storecfg, $src_volid, $snapname);
 	my $dst_path = PVE::Storage::path($storecfg, $dst_volid);
 
+    #BEGIN addition
+    my $src_storage_plugin = PVE::Storage::Plugin->lookup($src_scfg->{type});
+    my $dst_storage_plugin = PVE::Storage::Plugin->lookup($dst_scfg->{type});
+
+    # in many cases the storage may have a better idea how to convert:
+    # if src and dst format is the same
+    # and src_storeid is dst_storeid
+    # and the storage has the feature
+    # and the feature is implemented as volume_copy / volume_snapshot_copy
+    # let the storage do the work as it quite sure is faster
+    if ( $src_format eq $dst_format ) {
+        if( $src_storeid eq $dst_storeid ) {
+            # this is the same storage
+            # and storage is capable of materializing snaps
+            if( $snapname ) {
+                my $canCopySnap = PVE::Storage::volume_has_feature($storecfg, 'copy', $src_volid, $snapname, undef) && $src_storage_plugin->can('volume_snapshot_copy');
+                if( $canCopySnap ) {
+                    print "delegate to storage plugin volume_snapshot_copy (snap $snapname)\n";
+                    $src_storage_plugin->volume_snapshot_copy($src_scfg, $src_volname, $snapname, $dst_volname);
+
+                    $src_storage_plugin->deactivate_volume($src_storeid, $src_scfg, $src_volname, $snapname);
+
+                    return 1;
+                }
+            }
+
+            my $canCopyVolume = PVE::Storage::volume_has_feature($storecfg, 'copy', $src_volid, undef, undef) && $src_storage_plugin->can('volume_copy');
+            if ( $canCopyVolume ) {
+                print "delegate to storage plugin: volume_copy (base)\n";
+                $src_storage_plugin->volume_copy($src_scfg, $src_volname, $dst_volname);
+
+                $src_storage_plugin->deactivate_volume($src_storeid, $src_scfg, $src_volname, $snapname);
+
+                return 1;
+            }
+        }
+        # @todo: two zfs-storages might be able to receive stream from each other
+    }
+    #END addition
+
 	my $cmd = [];
 	push @$cmd, '/usr/bin/qemu-img', 'convert', '-p', '-n';
 	push @$cmd, '-l', "snapshot.name=$snapname" if($snapname && $src_format eq "qcow2");
@@ -6487,6 +6527,11 @@
 
 	eval  { run_command($cmd, timeout => undef, outfunc => $parser); };
 	my $err = $@;
+
+    # added: deactivate the src-volume, even on failure
+    # this can be safely called as qemu_img_convert is never called on a running volume (that is not a snap)
+    $src_storage_plugin->deactivate_volume($src_storeid, $src_scfg, $src_volname, $snapname);
+
 	die "copy failed: $err" if $err;
     }
 }