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

[John Carrier]

Alexey, 

If you are using the HCA to offload PI calculation on the server, why not use a CRC between the client and server that is optimal for software calculations.  The DIX architecture from SNIA does not require the PI calculation to extend to the app layer and describes translation between segments of the path.

--jc

-----Original Message-----
From: twg-bounces at lists.opensfs.org [mailto:twg-bounces at lists.opensfs.org] On Behalf Of Alexey Lyashkov
Sent: Friday, April 20, 2012 10:39 PM
To: Andreas Dilger
Cc: AndrewPerepechko; twg at lists.opensfs.org
Subject: Re: [Twg] T10 End-to-End Data Integrity HLD


On Apr 20, 2012, at 08:41, Andreas Dilger wrote:

> 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. 
> 
i forget one note, in case T10 DIF OSS CPU isn't included into CRC verification - it's done by raid/sas adapter transparency so we will dramatically reduce load on OSS node with that type checksumming enabled.
from OSC view - not have differences in handling EIO error - if it's real disk IO error or it's error during network transmitting, in both cases we need resend a data to OSS from a client.
so i think we don't need any separation for both these cases.


--------------------------------------------
Alexey Lyashkov
alexey_lyashkov at xyratex.com




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