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 And the resync was thus guided by an out-of-date 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 > > I wrote a script (attached) to recreate what happened, using some loop > devices. It works fine if BITMAP=none, and fails with BITMAP=internal. > > Jim
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