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

[Andrew Perepechko]

Hi Johann!

The original design does not cover metadata integrity. Guard tag value 0xffff can be used to avoid guard tag integrity checks on specific (metadata) sectors.

If metadata is to be included in integrity checks, then I/O replay should be implemented for recoverable errors. Since T10 tag mismatches don't seem to be
the only possible source of recoverable errors, this looks like an existing defect in current BRW RPC handling/async_journal implementation (?).

Andrew
  ----- Original Message ----- 
  From: Johann Lombardi 
  To: Alexey Lyashkov 
  Cc: John Carrier ; twg at lists.opensfs.org ; discuss at lists.opensfs.org ; AndrewPerepechko 
  Sent: Tuesday, April 24, 2012 10:03 PM
  Subject: Re: [Discuss] [Twg] T10 End-to-End Data Integrity HLD


  On Sun, Apr 22, 2012 at 5:36 AM, Alexey Lyashkov <alexey_lyashkov at xyratex.com> wrote:
    Why not? HCA provide a T10 checksumming when obdfilter (osd) submit a IO request - so it's before a call bio_done() function and before send a reply to client.
     
    so we may don't want a commit as HCA verify a checksum and it's correct.

  I was actually concerned by checksum errors when committing metadata blocks to disk. That said, i assume that the low level driver is supposed to resubmit the I/O several times (ideally via multipath) on checksum errors and ultimately triggers a failover (to replay the I/O), right?

  Cheers,
  Johann
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