Subject: Re: Why my life is sucking. Part 2.
To: None <email@example.com>
From: Alan Barrett <firstname.lastname@example.org>
Date: 01/18/2001 16:35:07
On Thu, 18 Jan 2001, Greg Oster wrote:
> There are some serious consequences to doing *ANYTHING* to data on a
> RAID set before the parity rewrite completes. If the parity is
> not correct for a given stripe, and you write real data to a portion
> of that stripe, old (and *incorrect*) parity will be used to create the
> new parity, and that new parity will also be *incorrect*. If a component
> fails before that incorrect parity gets fixed, and that component was
> a 'data' portion of that stripe, that data *WILL* be reconstructed
> incorrectly. And it won't matter if fsck had just updated that data block -
> the reconstruction will get it *wrong*. So even allowing fsck and the
> parity rewrite to happen at the same time is stretching things a little...
I can see that this concern applies to flavours of RAID that use real
parity (like RAID4 and RAID5). Does it also apply to RAID1, where the
"parity" is actually a copy of the data, and calculating the parity
doesn't require any XOR operations?
--apb (Alan Barrett)