[Twg] T10 End-to-End Data Integrity HLD

[Alexey Lyashkov]

On Apr 17, 2012, at 11:06, Andreas Dilger wrote:
> 
>>> One of the attractive features of the Merkle tree design is that it doesn't impose any extra overhead on the bulk RPC transmission, since the checksum sent with the RPC is distilled down to a single number, regardless of whether it is a single checksum on the data as is done today, or a hash of individual sector/page/chunk checksums as is proposed in both of our designs.  Similarly, this avoids the need to store long lists of GRD+REF+APP tags on large pages (which is really the smallest unit of coherency on the client), as would be needed with the straight T10-DIX implementation (128 * 8 bytes for a 64kB PAGE_SIZE with 512-byte sectors).
>> 
>> From a technical point of view, the tradeoff here is between transmitting a small amount of data (4k per 1MB) and recalculating that data on the servers.  Depending on where/how often we re-verify the checksums, we could remove the recalculation from the server entirely.
> 
> That is potentially true, but if the checksums are not verified until you get down to the disk, if there ever is a real checksum error you won't have any idea where the error is being introduced.


I may wrong, but I think, disk controller will verify checksum before put to the disk.
so we will have a write error if checksum is wrong.



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Alexey Lyashkov
alexey_lyashkov at xyratex.com