- by Kjell Andreassen
Short version: Is it safe to do mdadm --zero-superblock /dev/sdd on a disk with a partition (dev/sdd1), filesystem and data? Will the partition be mountable and the data still there? Longer version: I used to have a raid6 array but decided to dismantle it. The disks from the array are now used as non-raid disks. The superblocks were cleared: sudo mdadm --zero-superblock /dev/sdd The disks were repartitioned with fdisk and filesystems created with mfks.ext4. All disks where mounted and everything worked fine. Today, a couple of weeks later, one of the disks is failing to be recognized when trying to mount it, or rather the single partition on it. sudo mount /dev/sdd1 /mnt/tmp mount: special device /dev/sdd1 does not exist fdisk claims there to be a partition on it: sudo fdisk -l /dev/sdd Disk /dev/sdd: 2000.4 GB, 2000398934016 bytes 255 heads, 63 sectors/track, 243201 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0xb06f6341 Device Boot Start End Blocks Id System /dev/sdd1 1 243201 1953512001 83 Linux Of course mount is right, the device /dev/sdd1 is not there, I'm guessing udev did not create it because of the mdadm data still on it: sudo mdadm --examine /dev/sdd /dev/sdd: Magic : a92b4efc Version : 1.2 Feature Map : 0x0 Array UUID : b164e513:c0584be1:3cc53326:48691084 Name : pringle:0 (local to host pringle) Creation Time : Sat Jun 16 21:37:14 2012 Raid Level : raid6 Raid Devices : 6 Avail Dev Size : 3907027120 (1863.02 GiB 2000.40 GB) Array Size : 15628107776 (7452.06 GiB 8001.59 GB) Used Dev Size : 3907026944 (1863.02 GiB 2000.40 GB) Data Offset : 2048 sectors Super Offset : 8 sectors State : clean Device UUID : 3ccaeb5b:843531e4:87bf1224:382c16e2 Update Time : Sun Aug 12 22:20:39 2012 Checksum : 4c329db0 - correct Events : 1238535 Layout : left-symmetric Chunk Size : 512K Device Role : Active device 3 Array State : AA.AAA ('A' == active, '.' == missing) My mdadm --zero-superblock apparently didn't work. Can I safely try it again without losing data? If not, are there any suggestion on what do to? Not starting mdadm at all on boot might be a (somewhat unsatisfactory) solution.