diff --git a/btrbk b/btrbk
index d71742f..c4ece72 100755
--- a/btrbk
+++ b/btrbk
@@ -254,9 +254,9 @@ my %raw_info_sort = (
   # kdf_* (generated by kdf_backend)
  );
 
-my %url_cache;       # map URL to btr_tree node
 my %raw_url_cache;   # map URL to (fake) btr_tree node
 my %mountpoint_cache;# map HOST to btrfs mount points
+my %spec_cache;      # map HOST:fs_spec (aka device) to btr_tree node
 my %uuid_cache;      # map UUID to btr_tree node
 my %realpath_cache;  # map URL to realpath (symlink target)
 
@@ -370,9 +370,6 @@ sub SUBVOL_LIST {
   my $vol = shift; my $t = shift // "SUBVOL_LIST"; my $svl = vinfo_subvol_list($vol);
   print STDERR "$t:\n  " . join("\n  ", map { "$vol->{PRINT}/./$_->{SUBVOL_PATH}\t$_->{node}{id}" } @$svl) . "\n";
 }
-sub URL_CACHE {
-  print STDERR "URL_CACHE:\n" . join("\n", (sort keys %url_cache)) . "\n";
-}
 
 
 sub ABORTED($;$)
@@ -2061,17 +2058,22 @@ sub btr_tree($$$$)
   my $spec = shift || die;  # aka device
   my $mountpoints = shift || die; # all known mountpoints for this filesystem: arrayref of { file, subvolid }
   die unless($vol_root_id >= 5);
-  # NOTE: we need an ID (provided by btrfs_subvolume_show()) in order
-  # to determine the anchor to our root path (since the subvolume path
-  # output of "btrfs subvolume list" is ambigous, and the uuid of the
-  # btrfs root node cannot be resolved).
 
-  # man btrfs-subvolume:
-  #   Also every btrfs filesystem has a default subvolume as its initially
-  #   top-level subvolume, whose subvolume id is 5(FS_TREE).
-  my %tree = ( id => 5,
+  # return parsed tree from %spec_cache if present
+  my $vol_host_spec = ($vol->{HOST} // "localhost") . ':' . $spec;
+  my $cached_tree = $spec_cache{$vol_host_spec};
+  TRACE "spec_cache " . ($cached_tree ? "HIT" : "MISS") . ": $vol_host_spec";
+  if($cached_tree) {
+    TRACE "btr_tree: returning cached tree at id=$vol_root_id";
+    my $node = $cached_tree->{ID_HASH}{$vol_root_id};
+    ERROR "Unknown subvolid=$vol_root_id in btrfs tree of $vol_host_spec" unless($node);
+    return $node;
+  }
+
+  # assemble subvolume tree
+  my %tree = ( id => 5, # top-level subvolume id is always 5 (by btrfs spec)
                is_root => 1,
-               spec => $spec,
+               host_spec => $vol_host_spec, # unique identifier, e.g. "localhost:/dev/sda1"
                MOUNTPOINTS => $mountpoints, # { file, spec, node }
                SUBTREE => []
               );
@@ -2156,6 +2158,7 @@ sub btr_tree($$$$)
   TRACE "btr_tree: returning tree at id=$vol_root->{id}";
   VINFO($vol_root, "node") if($loglevel >=4);
 
+  $spec_cache{$vol_host_spec} = \%tree;
   return $vol_root;
 }
 
@@ -2227,26 +2230,6 @@ sub _is_child_of
 }
 
 
-sub _fill_url_cache
-{
-  my $node = shift;
-  my $abs_path = shift;
-  my $node_subdir = shift;
-  TRACE "_fill_url_cache: $abs_path" . ($node_subdir ? " (subdir=$node_subdir)" : "");
-
-  # traverse tree from given node and update tree cache
-  $url_cache{$abs_path} = $node unless(defined($node_subdir));
-  foreach(@{$node->{SUBTREE}}) {
-    my $rel_path = $_->{REL_PATH};
-    if(defined($node_subdir)) {
-      next unless($rel_path =~ s/^\Q$node_subdir\E\///);
-    }
-    _fill_url_cache($_, $abs_path . '/' . $rel_path, undef);
-  }
-  return undef;
-}
-
-
 sub _get_longest_match
 {
   my $node = shift;
@@ -2264,20 +2247,6 @@ sub _get_longest_match
 }
 
 
-# reverse path lookup
-sub get_cached_url_by_uuid($)
-{
-  my $uuid = shift;
-  my @result;
-  while(my ($url, $node) = each(%url_cache)) {
-    next if($node->{is_root});
-    next unless($node->{uuid} eq $uuid);
-    push @result, $url;
-  }
-  return @result;
-}
-
-
 sub vinfo($;$)
 {
   my $url = shift // die;
@@ -2455,51 +2424,32 @@ sub vinfo_init_root($;@)
 {
   my $vol = shift || die;
   my %opts = @_;
-  my $tree_root;
 
-  # use cached info if present
-  $tree_root = $url_cache{$vol->{URL}};
-  TRACE "url_cache " . ($tree_root ? "HIT" : "MISS") . ": URL=$vol->{URL}";
-  unless($tree_root) {
-    if(my $real_path = $realpath_cache{$vol->{URL}}) {
-      my $real_url = $vol->{URL_PREFIX} . $real_path;
-      $tree_root = $url_cache{$real_url};
-      TRACE "url_cache " . ($tree_root ? "HIT" : "MISS") . ": REAL_URL=$real_url";
-    }
-  }
+  # resolve btrfs tree from mount point
+  my ($mnt_path, $real_path, $subvolid, $spec, $spec_mounts) = btrfs_mountpoint($vol);
+  return undef unless($mnt_path && $real_path && $subvolid);
 
-  unless($tree_root) {
-      # btrfs tree is not yet cached, read it from mount point
-      my ($mnt_path, $real_path, $subvolid, $spec, $spec_mounts) = btrfs_mountpoint($vol);
-      return undef unless($mnt_path && $real_path && $subvolid);
-      my $mnt_tree_root = $url_cache{$vol->{URL_PREFIX} . $mnt_path};
-      unless($mnt_tree_root) {
-        # read btrfs tree for the mount point
-        my $mnt_vol = vinfo($vol->{URL_PREFIX} . $mnt_path, $vol->{CONFIG});
-        $mnt_tree_root = btr_tree($mnt_vol, $subvolid, $spec, $spec_mounts);
-        _fill_url_cache($mnt_tree_root, $mnt_vol->{URL});
-      }
+  # read btrfs tree for the mount point
+  my $mnt_vol = vinfo($vol->{URL_PREFIX} . $mnt_path, $vol->{CONFIG});
+  my $mnt_tree_root = btr_tree($mnt_vol, $subvolid, $spec, $spec_mounts);
+  return undef unless($mnt_tree_root);
 
-      # find longest match in tree
-      my $ret = _get_longest_match($mnt_tree_root, $mnt_path, $real_path) // die;
-      $tree_root = $ret->{node};
-
-      # set NODE_SUBDIR if $vol->{PATH} points to a regular (non-subvolume) directory.
-      # in other words, "PATH=<path_to_subvolume>/NODE_SUBDIR"
-      my $node_subdir = $real_path;
-      die unless($node_subdir =~ s/^\Q$ret->{path}\E//);  # NOTE: $ret->{path} has trailing slash!
-      $node_subdir =~ s/\/+$//;
-      $vol->{NODE_SUBDIR} = $node_subdir if($node_subdir ne '');
-
-      $vol->{MOUNTPOINT} = $mnt_path;
-      $vol->{MOUNTPOINT_NODE} = $mnt_tree_root;
-
-      _fill_url_cache($tree_root, $vol->{URL}, $vol->{NODE_SUBDIR});
-  }
+  # find longest match in btrfs tree
+  my $ret = _get_longest_match($mnt_tree_root, $mnt_path, $real_path) // die;
+  my $tree_root = $ret->{node};
   return undef unless($tree_root);
 
+  # set NODE_SUBDIR if $vol->{PATH} points to a regular (non-subvolume) directory.
+  # in other words, "PATH=<path_to_subvolume>/NODE_SUBDIR"
+  my $node_subdir = $real_path;
+  die unless($node_subdir =~ s/^\Q$ret->{path}\E//);  # NOTE: $ret->{path} has trailing slash!
+  $node_subdir =~ s/\/+$//;
+  $vol->{NODE_SUBDIR} = $node_subdir if($node_subdir ne '');
   $vol->{node} = $tree_root;
 
+  $vol->{MOUNTPOINT} = $mnt_path;
+  $vol->{MOUNTPOINT_NODE} = $mnt_tree_root;
+
   return $tree_root;
 }
 
@@ -2523,6 +2473,7 @@ sub vinfo_init_raw_root($;@)
     # create fake btr_tree
     $tree_root = { id => 5,
                    is_root => 1,
+                   host_spec => 'raw_tree@' . $droot->{URL}, # for completeness (this is never used)
                    GEN_MAX => 1,
                    SUBTREE => [],
                    UUID_HASH => {},
@@ -2749,7 +2700,6 @@ sub vinfo_inject_child($$$;$)
   return undef unless(add_btrbk_filename_info($node, $raw_info));
 
   $vinfo_child->{node} = $node;
-  $url_cache{$vinfo_child->{URL}} = $node;
   TRACE "vinfo_inject_child: injected child id=$node->{id} to $vinfo->{PRINT}";
   return $vinfo_child;
 }
@@ -4280,13 +4230,9 @@ sub _origin_tree
   # cache a bit, this might be large
   $nodelist //= [ (sort { $a->{REL_PATH} cmp $b->{REL_PATH} } values %uuid_cache) ];
 
-  my @url = get_cached_url_by_uuid($uuid);
   my $out_path;
-  if(scalar @url) {
-    $out_path = join(" === ", sort map { vinfo($_)->{PRINT} } @url);
-  } else {
-    $out_path = _fs_path($node);
-  }
+  $out_path = _fs_path($node);
+
   my $prefix_spaces = ' ' x (($depth * 4) - ($prefix ? 4 : 0));
   push(@$lines, { tree          => "${prefix_spaces}${prefix}$out_path",
                   uuid          => $node->{uuid},