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

Mike Fedyk
2002-05-17T18:30:13Z

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