NeilBrown wrote: > On Wed, 20 May 2015 02:31:50 -0400 Jim Paris <jim@xxxxxxxx> wrote: > > > NeilBrown wrote: > > > On Tue, 19 May 2015 10:12:40 -0400 Jim Paris <jim@xxxxxxxx> wrote: > > > > > > > I had a raid1 mirror consisting of big partitions on two disks. > > > > The first disk was 2TB, partitioned like this: > > > > > > > > [--sda1(128M)--][-------sda2(~2T)--------------] > > > > > > > > The second disk was 3TB, partitioned like this: > > > > > > > > [--sdb1(128M)--][-------sdb2(~3T)------------------------------------] > > > > > > > > sda2 and sdb2 were part of the array, which was only ~2TB in size due > > > > to the smaller disk. > > > > > > > > I realized that I needed to add a BIOS boot partition to the 3TB disk, > > > > so I removed sdb2 from the array, and repartitioned sdb like this: > > > > > > > > [--sdb1(128M)--][--sdb2(1M)--][-------sdb3(~3T)----------------------] > > > > > > > > Then I added sdb3 to the array. And lost all my data. :( > > > > > > > > What happened was that the last sector of the big partition did not > > > > change location. So the metadata (0.90) at the end was still present. > > > > > > This is one of the big reasons why 1.x was invented. > > > > > > > Adding sdb3 to the array was considered a "re-add" because the UUID > > > > and array sizes still matched the array, even though the partition > > > > itself shrank. And the resync was thus guided by an out-of-date > > > > bitmap, which caused very little data to actually be written to sdb3, > > > > so half the reads from the array started returning junk. Once the > > > > filesystem got involved, the result was rapid corruption. > > > > > > > > If I had not been using write-intent bitmaps, everything would have > > > > worked fine. I only recently started using bitmaps, and never had any > > > > problems with adjusting partitions like this before that. > > > > > > > > Perhaps mdadm can be more careful here -- for example, maybe checking > > > > the actual device size and not just the "used dev size" when > > > > determining whether to trust the bitmap. > > > > > > It is perfectly acceptable to have the various devices in an array of > > > different sizes. Unfortunately I don't think there is anything that mdadm > > > can usefully do here. > > > > > > Thanks for the report anyway, > > > NeilBrown > > > > Hi Neil, > > > > Can we add u64 device_size to bitmap_super_t, and ensure that it > > matches the actual current device size before trusting the bitmap? > > Well .... we could, but the bitmap_super is currently the same on all > devices. This would make it different. > And if we a going to change the metadata, why not just convert from 0.90 to > 1.0? My thinking was that the extra field could be added to bitmap_super automatically -- just start writing it now, but only use it to determine bitmap validity if the current value is non-zero. No explicit user-visible conversion. I see your point; it's a bit strange to change outdated stuff. But I also feel that if there's something mdadm could have done to prevent my data loss, that's worth putting in there. > mdadm --stop /dev/mdXX > mdadm --assemble /dev/mdXX --update=metadata /dev/...list-of-devices.... > > You might need to remove the bitmap first, and add it back afterwards. Cool. Much simpler than what's currently listed in the wiki for that conversion. Thanks Neil. xJim > > NeilBrown -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
