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# backingStoreIdentity

A unique identifier for the backing store used by the system.

```
var backingStoreIdentity: Data? { get }
```

## Discussion

Changes to this identifier indicate that the system has dropped its backing store and is creating a new one. The system may create a new backing store if the old store becomes corrupted. The file provider extension can also request a new backing store by calling [`reimportItems(below:completionHandler:)`](/documentation/FileProvider/NSFileProviderManager/reimportItems(below:completionHandler:)).

While rebuilding the backing store, the system invalidates any extension instances associated with the domain. As a result, the system guarantees that the [`backingStoreIdentity`](/documentation/FileProvider/NSFileProviderDomain/backingStoreIdentity) remains stable throughout the lifetime of an [`NSFileProviderReplicatedExtension`](/documentation/FileProvider/NSFileProviderReplicatedExtension) instance.

> Note:
> This property is only available on file provider extensions based on the ``doc://com.apple.fileprovider/documentation/FileProvider/NSFileProviderReplicatedExtension`` protocol.

---

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