Re: [PATCH 0/4] (RESEND) ext3[34] barrier changes

[Jamie Lokier]

Chris Mason wrote:
> write log blocks
> flush #1
> write commit block
> flush #2
> write metadata blocks
> 
> I'd agree with Ted, there's a fairly small chance of things get reordered 
> around flush #1.

Except when it crosses an MD disk boundary.  Then it's really likely.

We could also ask if there's _any_ possibility, when they are a merged
single I/O, of them not getting written in the expected order?
What about when FUA is set, does that imply any order?

But it's all moot: Checksumming is the way forward here, no doubt.
Checksumming makes the multi-sector write "atomic or corrupt".  That's
the same expectation as a commit sector provides by itself, but
generalised to the whole journal entry.

-- Jamie
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