Messages in this thread | | | Date | Fri, 17 May 2002 18:35:37 -0700 | From | Mike Fedyk <> | Subject | Re: Thoughts on using fs/jbd from drivers/md |
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On Fri, May 17, 2002 at 07:34:10PM +0100, Stephen C. Tweedie wrote: > Hi, > > On Fri, May 17, 2002 at 11:29:42AM -0700, Mike Fedyk wrote: > > On Thu, May 16, 2002 at 04:17:49PM +0100, Stephen C. Tweedie wrote: > > > > 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? > > No. > > > What does it take to trigger the corruption? > > It just takes degraded mode, an unexpected power cycle, and concurrent > write activity. > > Degraded mode relies on the parity disk being in sync at all times ---
Doesn't degraded mode imply that there are not any parity disk(raid4)/stripe(raid5) updates?
> you can't recover data from the missing spindle unless that is true. > However, writes to a stripe are not atomic, and you can get a reboot > when, say, a write to one of the surviving data chunks has succeeded, > but the corresponding write to the parity disk has not. If this > happens, the parity is no longer in sync, and the data belonging to > the missing spindle in that stripe will be lost forever. > > > 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. > > If it was a clean shutdown and reboot, you're fine. >
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