On 2015-04-27 16:49 +1000, NeilBrown wrote:
> On Mon, 27 Apr 2015 08:37:59 +0200 (CEST) Jean-Baptiste Thomas
> <cau2jeaf1honoq@xxxxxxxxxxx> wrote:
>·
> > I'm looking for a way to get MD to operate in a mode in which
> > reading a sector from a RAID-1 device would not succeed until it
> > got matching data from at least two components.
>·
> No, there is no such thing.
Thanks, now I can move on to working on plan B.
> There "should" be no circumstance which would make it worth while.
> A drive may well report an error, but it should *never* report
> incorrect data as though it were correct. That is horribly
> broken.
Isn't it. <g>
> The cost of running in a "safe" mode would be high, and the
> likely benefit extremely low. So it is unlikely that anyone
> would use it for long. So implementing it seems rather
> pointless.
How high would the cost be ?
Seems to me that a 4-component RAID-1 with a 2-component quorum
would incur no more I/O or CPU overhead than, say, a 4-component
RAID-6. Less, in fact, unless parity computation is faster than
memcmp().
Given the choice between that sort of cost and the possibility
of massive data corruption because one drive had a hiccup, I
would not even THINK about running without it.
> That said: if someone were to provide an implementation I
> would certainly consider reviewing it and adding it to md.
Great. Don't think it'll be me, though. :-/
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