[dm-devel] [PATCHSET block#for-2.6.36-post] block: replace barrier with sequenced flush

[Vladislav Bolkhovitin]

Tejun Heo, on 08/23/2010 04:14 PM wrote:
>> I think that's correct and changing the priority of DM_ENDIO_REQUEUE
>> for REQ_FLUSH down to the lowest should be fine.
>> (I didn't know that FLUSH failure implies data loss possibility.)
>
> At least on ATA, FLUSH failure implies that data is already lost, so
> the error can't be ignored or retried.

In SCSI there are conditions when a command, including FLUSH 
(SYNC_CACHE), failed which don't imply lost data. For them the caller 
expected to retry the failed command. Most common cases are Unit 
Attentions and TASK QUEUE FULL status.

Vlad