Documentation: dm-integrity: Document an example of how the tunables relate.

should not be changed when reloading the target because the layout of disk

data depend on them and the reloaded target would be non-functional.

For example, on a device using the default interleave_sectors of 32768, a

block_size of 512, and an internal_hash of crc32c with a tag size of 4

bytes, it will take 128 KiB of tags to track a full data area, requiring

256 sectors of metadata per data area. With the default buffer_sectors of

128, that means there will be 2 buffers per metadata area, or 2 buffers

per 16 MiB of data.

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