diff --git a/.env.example b/.env.example
index 172b887..7d09efe 100644
--- a/.env.example
+++ b/.env.example
@@ -2,5 +2,13 @@
 DATABASE_URL=postgres://USER@localhost:5432/stl_library
 PORT=3000
 
+# Docker only: where data lives on the host. Both default to ./data beside
+# docker-compose.yml. DATA_DIR takes the model files, thumbnails and previews.
+DATA_DIR=/Volumes/Data/printhive
+# The database is set separately, because Postgres needs a filesystem with real
+# ownership and permissions — leave it on local disk if DATA_DIR is exFAT, FAT
+# or a network share.
+PGDATA_DIR=/Volumes/Data/printhive/pgdata
+
 # Thingiverse import — get a free app token at https://www.thingiverse.com/developers
 THINGIVERSE_TOKEN=
diff --git a/README.md b/README.md
index edfb6a7..36fcc64 100644
--- a/README.md
+++ b/README.md
@@ -59,17 +59,22 @@ Run the unit tests with `npm test`.
 
 ### Where your data lives
 
-With Docker, everything sits in folders next to `docker-compose.yml` (set `DATA_DIR` to put them elsewhere):
+With Docker, everything sits in folders on the host — `./data` beside `docker-compose.yml` unless `.env` says
+otherwise (`DATA_DIR` for the files, `PGDATA_DIR` for the database):
 
 | Folder | Holds |
 |---|---|
-| `data/pgdata` | The database: models, tags, collections, watches, spools, printers, settings (tokens and printer access codes live here) |
-| `data/uploads` | Your model files, as uploaded or downloaded |
-| `data/thumbnails` | Generated pictures, including plate images |
-| `data/glb` | Converted 3D previews for the viewer |
-| `data/extracted` | Files unpacked from archives — a cache |
+| `$PGDATA_DIR` | The database: models, tags, collections, watches, spools, printers, settings (tokens and printer access codes live here) |
+| `$DATA_DIR/uploads` | Your model files, as uploaded or downloaded |
+| `$DATA_DIR/thumbnails` | Generated pictures, including plate images |
+| `$DATA_DIR/glb` | Converted 3D previews for the viewer |
+| `$DATA_DIR/extracted` | Files unpacked from archives — a cache |
 
-A backup needs `data/pgdata` (or a `pg_dump`) and `data/uploads`; the other three rebuild themselves. Everything else in
+The database is set apart from the rest because Postgres needs a filesystem with real ownership and permissions —
+ext4, xfs, APFS and the like. exFAT, FAT and most network shares won't do, so keep `PGDATA_DIR` on local disk if the
+files live on one of those.
+
+A backup needs the database (or a `pg_dump`) and `uploads`; the other three rebuild themselves. Everything else in
 the container is replaced on each update, so nothing outside these folders is kept.
 
 Upgrading from a version that used Docker named volumes: stop the stack, run `tools/volumes-to-folders.sh` to copy the
diff --git a/docker-compose.yml b/docker-compose.yml
index 968d491..1c34ddd 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -6,7 +6,11 @@ services:
       POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:-printhive}
       POSTGRES_DB: printhive
     volumes:
-      - ${DATA_DIR:-./data}/pgdata:/var/lib/postgresql/data
+      # Set separately from DATA_DIR: Postgres needs a filesystem with real
+      # ownership and permissions (ext4, xfs, APFS...), which exFAT, FAT and
+      # most network shares don't provide. Keep it on local disk if the files
+      # live somewhere like that.
+      - ${PGDATA_DIR:-./data/pgdata}:/var/lib/postgresql/data
     healthcheck:
       test: ["CMD-SHELL", "pg_isready -U printhive -d printhive"]
       interval: 5s
@@ -33,7 +37,7 @@ services:
       MAKERWORLD_TOKEN: ${MAKERWORLD_TOKEN:-}
       PRINTABLES_TOKEN: ${PRINTABLES_TOKEN:-}
     volumes:
-      # Folders on the host, under ./data (set DATA_DIR to put them elsewhere).
+      # Folders on the host: ./data unless DATA_DIR says otherwise.
       # uploads and pgdata hold everything that matters; the other two rebuild.
       - ${DATA_DIR:-./data}/uploads:/app/uploads
       - ${DATA_DIR:-./data}/thumbnails:/app/thumbnails
diff --git a/tools/volumes-to-folders.sh b/tools/volumes-to-folders.sh
index cbef307..ab9b55f 100755
--- a/tools/volumes-to-folders.sh
+++ b/tools/volumes-to-folders.sh
@@ -8,9 +8,23 @@
 # again with nothing lost.
 set -euo pipefail
 
+# Same settings Compose uses, so the copy lands where the stack will look.
+if [ -f .env ]; then
+  DATA_DIR="${DATA_DIR:-$(grep -E '^DATA_DIR=' .env | tail -1 | cut -d= -f2-)}"
+  PGDATA_DIR="${PGDATA_DIR:-$(grep -E '^PGDATA_DIR=' .env | tail -1 | cut -d= -f2-)}"
+fi
 DATA_DIR="${DATA_DIR:-./data}"
+PGDATA_DIR="${PGDATA_DIR:-./data/pgdata}"
 VOLUMES=(pgdata uploads thumbnails glb extracted)
 
+# Where each volume's contents should end up.
+target_for() {
+  case "$1" in
+    pgdata) echo "$PGDATA_DIR" ;;
+    *) echo "$DATA_DIR/$1" ;;
+  esac
+}
+
 # Compose names volumes "<project>_<name>", the project being this folder's name
 # unless it's set elsewhere.
 PROJECT="${COMPOSE_PROJECT_NAME:-$(basename "$(pwd)")}"
@@ -20,13 +34,14 @@ if docker compose ps --status running --quiet 2>/dev/null | grep -q .; then
   exit 1
 fi
 
-echo "Project: $PROJECT"
-echo "Copying into: $DATA_DIR"
+echo "Project:  $PROJECT"
+echo "Files:    $DATA_DIR"
+echo "Database: $PGDATA_DIR"
 echo
 
 for name in "${VOLUMES[@]}"; do
   volume="${PROJECT}_${name}"
-  target="$DATA_DIR/$name"
+  target="$(target_for "$name")"
 
   if ! docker volume inspect "$volume" >/dev/null 2>&1; then
     echo "· $volume — no such volume, skipping (nothing to copy)"