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# kCFURLVolumeIdentifierKey

Key for the unique identifier of the resource’s volume, returned as a `CFType` object.

```
let kCFURLVolumeIdentifierKey: CFString!
```

## Discussion

This identifier can be used with the [`CFEqual(_:_:)`](/documentation/CoreFoundation/CFEqual(_:_:)) function to determine whether two file system resources are on the same volume.

The value of this identifier is not persistent across system restarts.

---

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