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# UserReportMediumBlockSize

Provides a report on the external device’s block size.

```
virtual kern_return_t UserReportMediumBlockSize(UInt64 *blockSize);
```

## Parameters

`blockSize`

On return, the external device’s block size.

## Return Value

A value that indicates the result of the report request. <doc://com.apple.documentation/documentation/DriverKit/kIOReturnSuccess> indicates success. For error definitions, see <doc://com.apple.documentation/documentation/iokit/iokit_constants>.

## Discussion

This call populates `blockSize` with the granularity of the block size, such as 512 bytes or 4096 bytes (4 KB).

---

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