Re: Thoughts on using fs/jbd from drivers/md

[Mike Fedyk <mfedyk@matchmail.com>]

On Thu, May 16, 2002 at 04:17:49PM +0100, Stephen C. Tweedie wrote:
> Hi,
> 
> On Thu, May 16, 2002 at 03:54:20PM +1000, Neil Brown wrote:
> > The basic idea is to provide journaling for md/RAID arrays.  There
> > are two reasons that one might want to do this:
> >  1/ crash recovery.  Both raid1 and raid5 need to reconstruct the
> >    redundancy after a crash.  For a degraded raid5 array, this is not
> >    possible and you can suffer undetected data corruption.
> >    If we have a journal of recent changes we can avoid the
> >    reconstruction and the risk of corruption.
> 
> Right.  The ability of soft raid5 to lose data in degraded mode over a
> reboot (including data that was not being modified at the time of the
> crash) is something that is not nearly as widely understood as it
> should be, and I'd love for us to do something about it.

Are there workarounds to avoid this problem?

What does it take to trigger the corruption?

I ask this because I have used a degraded raid5 because the source drive
would become a member, but I needed to copy the data first.  While doing so,
I had to reboot a couple times to reconfigure the boot loader.  All seems to
be working fine on the system today though.

Thanks,

Mike