Re: [PATCH] mmc: Multi-sector writes

[Pierre Ossman <drzeus-list@drzeus.cx>]

Pavel Machek wrote:

>
>Maybe the card is pretty close to going to crash, but... two disk
>successive disk errors still should not be cause for journal
>corruption.
>
>[Also errors could be corelated. Imagine severe overheat. You'll
>successive failing writes, but if you let cool it down, you'll still
>have working media... only with corrupt journal :-)]
>								Pavel
>  
>

Hmm... So how is this handled in other systems? E.g. if you yank a USB
device whilst there is a lot of outstanding data inside the device that
hasn't been ack:d yet.

The way I see it, filesystems should assume the following at a failed write:

* 0-n sectors were written successfully.
* 0-1 sectors have corrupt data.
* 0-m sectors have old data.
* The lower layer will report back 0-k successfully written sectors,
where k <= n.

So perhaps the best course of action is to remove the sector-by-sector
failsafe? It will increase the chance of k < n, but it will not break
above assumption.

Rgds
Pierre

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