Mike Snitzer wrote:
mdadm 2.4.1 through 2.5.6 works. mdadm-2.6's "Improve allocation and use of space for bitmaps in version1 metadata" (199171a297a87d7696b6b8c07ee520363f4603c1) would seem like the offending change. Using 1.2 metdata works. I get the following using the tip of the mdadm git repo or any other version of mdadm 2.6.x: # mdadm --create /dev/md2 --run -l 1 --metadata=1.0 --bitmap=internal -n 2 /dev/sdf --write-mostly /dev/nbd2 mdadm: /dev/sdf appears to be part of a raid array: level=raid1 devices=2 ctime=Wed Oct 17 10:17:31 2007 mdadm: /dev/nbd2 appears to be part of a raid array: level=raid1 devices=2 ctime=Wed Oct 17 10:17:31 2007 mdadm: RUN_ARRAY failed: Input/output error mdadm: stopped /dev/md2 kernel log shows: md2: bitmap initialized from disk: read 22/22 pages, set 715290 bits, status: 0 created bitmap (350 pages) for device md2 md2: failed to create bitmap (-5) md: pers->run() failed ... md: md2 stopped. md: unbind<nbd2> md: export_rdev(nbd2) md: unbind<sdf> md: export_rdev(sdf) md: md2 stopped.
I would start by retrying with an external bitmap, to see if for some reason there isn't room for the bitmap. If that fails, perhaps no bitmap at all would be a useful data point. Was the original metadata the same version? Things moved depending on the exact version, and some --zero-superblock magic might be needed. Hopefully Neil can clarify, I'm just telling you what I suspect is the problem, and maybe a non-destructive solution.
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