Re: Paranoid mode for RAID-1 ?

[NeilBrown <neilb@suse.de>]

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On Mon, 27 Apr 2015 08:37:59 +0200 (CEST) Jean-Baptiste Thomas
<cau2jeaf1honoq@laposte.net> 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.
> 
> Recent experience[1] suggests that a transient problem in one
> disk can completely hose a four way RAID-1 array, which is
> otherwise supposed to still be fine after a triple total
> failure. I'm hoping that a paranoid mode would have prevented
> that.
> 
> If there is such a thing, PLEASE tell me. If not, please tell me 
> so I don't waste any more time looking for it.

No, there is no such thing.

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.

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.

That said: if someone were to provide an implementation I would certainly
consider reviewing it and adding it to md.

NeilBrown

> 
> [1] "Massive RAID-1 desync"
> http://www.spinics.net/lists/raid/msg48681.html
> http://marc.info/?l=linux-raid&m=143003812706563&w=2
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