RFC: detect and manage power cut on MLC NAND

[Artem Bityutskiy]

On Mon, 2015-03-23 at 20:05 +0100, Boris Brezillon wrote:
> > If we sacrifice another page, we could store a copy of the VID header
> > there, in case the first copy gets corrupted. IOW, we'd have:
> > 
> > 	ECH, VIDH#1, VIDH#2, User Data.
> 
> What do you mean by 'sacrificing another page', are you talking about
> the one paired with the VID header page ?
> If that's the case, then we cannot write anything on it (even a VID
> header backup), because if the PROGRAM operation is interrupted both
> pages (VIDH#1 and #2) could be corrupted.

Just this:

Page 0: ECH
Page 1: VIDH#1 (+all the ECH data)
Page 2: VIDH#2 (same as VIDH#1)

VIDH#1 and #2 are not in paired pages, so I expect one of them to always
be good.

If pages 0,1;2,3;4,5;etc are paired, we may lose ECH sometimes, should
not be catastrophic. I wonder though, if this pairing scheme is
realistic?

In case of a larger pairing step we seem to be always OK and will always
have a valid ECH and VIDH.

Do I miss something?