More tmpfs impermanence fixes.

common/global/backup.nix

@@ -6,8 +6,7 @@ let
   btrfs = "${btrfsPkg}/bin/btrfs";
   snapshotBackup = pkgs.writeScript "kopia-snapshot-backup" (builtins.readFile ./kopia-snapshot-backup.sh);
   backupScript = pkgs.writeShellScript "backup-persist" ''
-      target_path="/persist"
-      snapshot_path="$target_path/kopia-backup-snapshot"
+      target_path="${config.custom.impermanence.persistPath}"
       KOPIA_CHECK_FOR_UPDATES=false
 
       ${kopia} repository connect server \
@@ -16,18 +15,29 @@ let
         -p "$(cat ${config.sops.secrets.kopia.path})" \
       || exit 1
 
-      [ -e "$snapshot_path" ] && ${btrfs} subvolume delete "$snapshot_path"
+      # Check if target_path is on btrfs filesystem
+      fs_type=$(stat -f -c %T "$target_path")
 
-      ${btrfs} subvolume snapshot -r "$target_path" "$snapshot_path"
+      if [ "$fs_type" = "btrfs" ]; then
+        # On btrfs: use snapshot for consistency
+        snapshot_path="$target_path/kopia-backup-snapshot"
+        [ -e "$snapshot_path" ] && ${btrfs} subvolume delete "$snapshot_path"
+        ${btrfs} subvolume snapshot -r "$target_path" "$snapshot_path"
 
-      # --no-send-snapshot-path due to https://github.com/kopia/kopia/issues/4402
-      # Exclude btrfs replication snapshots (they appear as empty dirs in the snapshot anyway)
-      ${kopia} snapshot create --no-send-snapshot-report --override-source "$target_path" \
-        --ignore "services@*" \
-        --ignore "services-standby/services@*" \
-        -- "$snapshot_path"
+        # --no-send-snapshot-path due to https://github.com/kopia/kopia/issues/4402
+        # Exclude btrfs replication snapshots (they appear as empty dirs in the snapshot anyway)
+        ${kopia} snapshot create --no-send-snapshot-report --override-source "$target_path" \
+          --ignore "services@*" \
+          --ignore "services-standby/services@*" \
+          -- "$snapshot_path"
+
+        ${btrfs} subvolume delete "$snapshot_path"
+      else
+        # On non-btrfs (e.g., ext4): backup directly without snapshot
+        ${kopia} snapshot create --no-send-snapshot-report --override-source "$target_path" \
+          -- "$target_path"
+      fi
 
-      ${btrfs} subvolume delete "$snapshot_path"
       ${kopia} repository disconnect
   '';
 in