diff --git a/Containers/mastercontainer/start.sh b/Containers/mastercontainer/start.sh
index 77587767..f3b1723b 100755
--- a/Containers/mastercontainer/start.sh
+++ b/Containers/mastercontainer/start.sh
@@ -63,6 +63,19 @@ else
 fi
 
 # Check for other options
+if [ -n "$NEXTCLOUD_DATADIR" ]; then
+    if ! echo "$NEXTCLOUD_DATADIR" | grep -q "^/mnt/" \
+    && ! echo "$NEXTCLOUD_DATADIR" | grep -q "^/media/"
+    then
+        echo "You've set NEXTCLOUD_DATADIR but not to an allowed value.
+The string must start with '/mnt/' or '/media/'. E.g. '/mnt/ncdata'"
+        exit 1
+    elif [ "$NEXTCLOUD_DATADIR" = "/mnt/" ] || [ "$NEXTCLOUD_DATADIR" = "/media/" ]; then
+        echo "You've set NEXTCLOUD_DATADIR but not to an allowed value.
+The string must start with '/mnt/' or '/media/' and not be equal to these."
+        exit 1
+    fi
+fi
 if [ -n "$NEXTCLOUD_MOUNT" ]; then
     if ! echo "$NEXTCLOUD_MOUNT" | grep -q "^/mnt/" \
     && ! echo "$NEXTCLOUD_MOUNT" | grep -q "^/media/" \
diff --git a/Containers/nextcloud/entrypoint.sh b/Containers/nextcloud/entrypoint.sh
index 8778ab02..0e7e86ac 100644
--- a/Containers/nextcloud/entrypoint.sh
+++ b/Containers/nextcloud/entrypoint.sh
@@ -21,6 +21,15 @@ redis.session.lock_retries = -1
 redis.session.lock_wait_time = 10000
 REDIS_CONF
 
+# Check permissions in ncdata
+touch "/mnt/ncdata/this-is-a-test-file"
+if ! [ -f "/mnt/ncdata/this-is-a-test-file" ]; then
+    echo "The www-data user doesn't seem to have access rights in /mnt/ncdata.
+Did you maybe change the datadir and did forget to apply the correct permissions?"
+    exit 1
+fi
+rm "/mnt/ncdata/this-is-a-test-file"
+
 if [ -f /var/www/html/version.php ]; then
     # shellcheck disable=SC2016
     installed_version="$(php -r 'require "/var/www/html/version.php"; echo implode(".", $OC_Version);')"
@@ -223,6 +232,13 @@ if ! [ -f "/mnt/ncdata/skip.update" ]; then
     fi
 fi
 
+# Check if appdata is present
+# If not, something broke (e.g. changing ncdatadir after aio was first started)
+if [ -z "$(find "/mnt/ncdata/" -maxdepth 1 -mindepth 1 -type d -name "appdata_*")" ]; then
+    echo "Appdata is not present. Did you maybe change the datadir after aio was first started?"
+    exit 1
+fi
+
 # Apply one-click-instance settings
 echo "Applying one-click-instance settings..."
 php /var/www/html/occ config:system:set one-click-instance --value=true --type=bool
diff --git a/php/containers.json b/php/containers.json
index b9d423ef..2066a10c 100644
--- a/php/containers.json
+++ b/php/containers.json
@@ -96,7 +96,7 @@
           "writeable": true
         },
         {
-          "name": "nextcloud_aio_nextcloud_data",
+          "name": "%NEXTCLOUD_DATADIR%",
           "location": "/mnt/ncdata",
           "writeable": true
         },
@@ -215,7 +215,7 @@
           "writeable": true
         },
         {
-          "name": "nextcloud_aio_nextcloud_data",
+          "name": "%NEXTCLOUD_DATADIR%",
           "location": "/nextcloud_aio_volumes/nextcloud_aio_nextcloud_data",
           "writeable": true
         },
diff --git a/php/src/ContainerDefinitionFetcher.php b/php/src/ContainerDefinitionFetcher.php
index ddb8d280..60e92305 100644
--- a/php/src/ContainerDefinitionFetcher.php
+++ b/php/src/ContainerDefinitionFetcher.php
@@ -78,6 +78,11 @@ class ContainerDefinitionFetcher
                     if($value['name'] === '') {
                         continue;
                     }
+                } elseif ($value['name'] === '%NEXTCLOUD_DATADIR%') {
+                    $value['name'] = $this->configurationManager->GetNextcloudDatadirMount();
+                    if ($value['name'] === '') {
+                        continue;
+                    }
                 }
                 if($value['location'] === '%NEXTCLOUD_MOUNT%') {
                     $value['location'] = $this->configurationManager->GetNextcloudMount();
diff --git a/php/src/Data/ConfigurationManager.php b/php/src/Data/ConfigurationManager.php
index f98cab2b..0a4bd990 100644
--- a/php/src/Data/ConfigurationManager.php
+++ b/php/src/Data/ConfigurationManager.php
@@ -309,4 +309,27 @@ class ConfigurationManager
             return $mount;
         }
     }
+
+    public function GetNextcloudDatadirMount() : string {
+        $mount = getenv('NEXTCLOUD_DATADIR');
+        if ($mount === false) {
+            $config = $this->GetConfig();
+            if (!isset($config['nextcloud_datadir']) || $config['nextcloud_datadir'] === '') {
+                $config['nextcloud_datadir'] = 'nextcloud_aio_nextcloud_data';
+            }
+            return $config['nextcloud_datadir'];
+        } else {
+            if(file_exists(DataConst::GetConfigFile())) {
+                $config = $this->GetConfig();
+                if (!isset($config['nextcloud_datadir'])) {
+                    $config['nextcloud_datadir'] = '';
+                }
+                if ($mount !== $config['nextcloud_datadir']) {
+                    $config['nextcloud_datadir'] = $mount;
+                    $this->WriteConfig($config);
+                }
+            }
+            return $mount;
+        }
+    }
 }