# Files and persistent storage

A deployment replaces the application filesystem with the files built for that version. Data written by the running app needs a persistent directory when it should survive that replacement.

Use `/tokay/data` for new code, or mark an existing application directory as persistent.

## Code resets while app owned data persists

Files included in the build are recreated on each deploy. This makes a deployment and rollback reproduce the version that was built.

Files under `/tokay/data` are different. They belong to the Service across deployments and restarts. Tokay also provides the path through `TOKAY_DATA_DIR` so the code can avoid hardcoding it.

A file written beside the source, such as `./uploads/photo.jpg`, is temporary unless that directory is marked persistent.

## Keep an existing application path

Open the **Persistent Storage** section in Service settings and add the directory the app already uses. Tokay also suggests write paths it detects in the code.

A newly attached persistent directory starts empty. If the build contains files at the same path, the empty persistent directory covers them on the next deployment. The confirmation explains this before the change is applied.

Detaching a directory stops mounting it but keeps its stored data. Deleting the data is a separate action. If important files already exist in a temporary path, rescue them before the current instance changes. See [Service files](service-files.md).

## Persistent data is protected outside the VM disk

Tokay replicates persistent directories away from the virtual machine's local disk. Periodic offsite snapshots provide another recovery point for severe failures or data that was deleted and later permanently purged.

## Choose persistence based on the kind of file

User uploads, generated reports, and a SQLite database file need persistent storage. Caches and temporary files usually should reset with the release.

Project databases such as Postgres, MySQL, MongoDB, and Redis manage their own durable storage. See [Databases](databases.md).