Dear Andreas, thanks for the quyick reply, and on a Sunday... In message <20160515153121.GA11365@xxxxxxxxxxxxxxx> you wrote: > On Sun, May 15, 2016 at 03:37:40PM +0200, Wolfgang Denk wrote: > > Trying to follow the overlay method in [1], I run into errors; guess I > > must be missing something: > > > > [1] https://raid.wiki.kernel.org/index.php/Recovering_a_failed_software_RAID#Making_the_harddisks_read-only_using_an_overlay_file > > I think you mixed two approaches to the same thing, the wiki shows > a) how to create overlays manually and b) offers some convenience > functions that do the same thing (the overlay create remove functions, > you define those functions once and then you can repeatedly call them, > basically giving you two commands overlay_create and overlay_remove). Yes, you are right. I now realized this, too. > And then call 'overlay_create' when you want your overlays, > and 'overlay_remove; overlay create' when an experiment > failed and you want to reset them to their original state. > > At the time you remove the overlays, all things using them > must also be gone, so mdadm --stop before overlay_remove. > (And make sure no raid is running for the disks you're > overlaying...) Thanks - this was the key that got me working. After creating the overlys, the system would automatically start the (incorrect) RAID arrays. After manually stopping these, I had write access to the overlays. Recovering my data was (fortunately) simple: 1) I zeroed the incorrect superblocks on all devices: # mdadm --zero-superblock /dev/mapper/sda # mdadm --zero-superblock /dev/mapper/sdb # mdadm --zero-superblock /dev/mapper/sdc # mdadm --zero-superblock /dev/mapper/sdd # mdadm --zero-superblock /dev/mapper/sde # mdadm --zero-superblock /dev/mapper/sdf 2) Then I forced an assemble of the array: # mdadm --assemble --force --verbose /dev/md2 --metadata=1.2 # $overlays mdadm: looking for devices for /dev/md2 mdadm: /dev/mapper/sda is identified as a member of /dev/md2, slot 1. mdadm: /dev/mapper/sdb is identified as a member of /dev/md2, slot 0. mdadm: /dev/mapper/sdc is identified as a member of /dev/md2, slot 2. mdadm: /dev/mapper/sdd is identified as a member of /dev/md2, slot 3. mdadm: /dev/mapper/sde is identified as a member of /dev/md2, slot 5. mdadm: /dev/mapper/sdf is identified as a member of /dev/md2, slot 4. mdadm: added /dev/mapper/sda to /dev/md2 as 1 mdadm: added /dev/mapper/sdc to /dev/md2 as 2 mdadm: added /dev/mapper/sdd to /dev/md2 as 3 mdadm: added /dev/mapper/sdf to /dev/md2 as 4 mdadm: added /dev/mapper/sde to /dev/md2 as 5 mdadm: added /dev/mapper/sdb to /dev/md2 as 0 mdadm: /dev/md2 has been started with 6 drives. And me was happy again. I owe you a beer or two. Please don't hesitate to remind me whenever we meet... Thanks again. Best regards, Wolfgang Denk -- DENX Software Engineering GmbH, Managing Director: Wolfgang Denk HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@xxxxxxx "You can have my Unix system when you pry it from my cold, dead fingers." - Cal Keegan -- 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
