Partiy error detection - was Re: ext3 journal on software raid (was Re: PROBLEM: Kernel 2.6.10 crashing repeatedly and hard)

Peter T. Breuer wrote:

And there is a risk of silent corruption on all raid systems - that is
well known. DIfferent raid systems do different thigs to compensate,
such as periodically recalculating the parity on everything. But when
you have redundant data and a corruption occurs, which of the two
datasets do you believe? You have to choose one of them! You guess
wrong half the time, if you guess ("you" is a raid system). Hence
"silent corruption".

Just on this point. With RAID-6 I guess you can get a majority rules type of ruling on which data 
block is the dud. Unless you come up with 3 different results in which case something is really not 
right in lego land.

I wonder perhaps about a userspace app that you can run to check all the parity blocks. On RAID-5 it 
should be able to tell you, you have a naff stripe, but on RAID-6 in theory if it's only a single 
drive that is a problem you should be able to correct the block.

Regards,
Brad