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

[Andreas Dilger]

On 2012-04-19, at 11:57, Alexey Lyashkov <alexey_lyashkov at xyratex.com> wrote:
> On Apr 19, 2012, at 01:55, Andreas Dilger wrote:
>> 
>> Based on the data in LU-1201, I think with Nehalem CPUs and multi-threaded ptlrpcd the checksum overhead will become a non-issue, and people will happily leave it enabled all the time.  The unfortunate thing is that the CRC16 used by T10-DIF has such poor software performance that I agree there is no option but to leave the verification to the hardware.
>> 
> Based on Xyratex test results - crc32c HW implementation isn't best choose, and multi thread ptlrpcd isn't help to improve a  OST side loading.
> yes, main problem is OST side, not a client side checksumming.
> 
> Typical speed is less 1Gb/s for crc32c hw, and it's less speed then adler may provide.
> Current top speed list - adler, crc32 hw based on (not crc32c), crc32c hw, both crc32c table implementation.

I think we both agree in any case that the current crc16-t10dif is not nearly as fast as any of these 32-bit checksums. This may prove to be a major discouragement to using T10-PI even if it is available. 

Cheers, Andreas