We probably mean the same thing (I hope). Practically speaking a acid
compliant database system does the following (abstract actions) when
commiting a transaction:
1) writing to the log
2) flush the log ((and wait for the write to finish)
3) do other things
4) before deleting the log / overwriting the log / if there is time and
nothing else to do write to the datafile
5) remove the transaction from the log
So write order consistency means: For applications expecting local disk
semantics (like the acid scenario described above), protocol C hehaves
like local disk.
This means it is safe to place database log files and data files on
different drbd devices as long as the protocol is C.
In't it ?
Regards,
Robert
Protocol C ensures write-ordering and consistency for one drbd instance
(the local and the remote drive); not across two drbds.
But that's neither worse nor better than two independent local disks,
which exhibit exactly the same behaviour, and has to be handled at the
application level.
Regards,
Lars
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