Full Discussion: Reconstructing RAID
Special Forums Hardware Filesystems, Disks and Memory Reconstructing RAID Post 302695721 by tonyaldr on Monday 3rd of September 2012 02:37:34 PM
Reconstructing RAID

I am trying to reconstruct a failed 4 disk RAID5 Western Digital ShareSpace device using 3 of the 4 disks connected via USB to an Ubuntu 12.04 machine. I get what seems like a successful re-assemble from -

mdadm --assemble --force /dev/md2 /dev/sde4 /dev/sdf4 /dev/sdg4
mdadm: /dev/md2 has been started with 3 drives (out of 4).
But then when I try to mount, it fails.  I am logged in as root and when I try to troubleshoot with mdadm, I get odd returns such as -
mdadm --examine /dev/md2
mdadm: No md superblock detected on /dev/md2.
Also, the system can't seem to find the volume -
vgscan -v
    Wiping cache of LVM-capable devices
    Wiping internal VG cache
  Reading all physical volumes.  This may take a while...
    Finding all volume groups
  No volume groups found

I read in some other posts that the WD system uses LVM2.  Could that be the issue?  Here is the output from mdadm --detail
mdadm --detail /dev/md2
        Version : 0.90
  Creation Time : Mon Oct 19 10:26:15 2009
     Raid Level : raid5
     Array Size : 5854981248 (5583.75 GiB 5995.50 GB)
  Used Dev Size : 1951660416 (1861.25 GiB 1998.50 GB)
   Raid Devices : 4
  Total Devices : 3
Preferred Minor : 2
    Persistence : Superblock is persistent

    Update Time : Sun Sep  2 15:22:50 2012
          State : clean, degraded 
 Active Devices : 3
Working Devices : 3
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 64K

           UUID : 4c4952ae:1477d756:234bdad8:bdaa1368
         Events : 0.9246753

    Number   Major   Minor   RaidDevice State
       0       8       84        0      active sync   /dev/sdf4
       1       8       68        1      active sync   /dev/sde4
       2       0        0        2      removed
       3       8      100        3      active sync   /dev/sdg4

Here's the result of the mount attempt-
mount -t auto dev/md2 /mnt/raid
mount: special device dev/md2 does not exist

Appreciate any assistance! Thanx!

Last edited by Neo; 11-21-2017 at 10:59 AM..
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VGSCAN(8)						      System Manager's Manual							 VGSCAN(8)

vgscan - scan all disks for volume groups and build /etc/lvmtab and /etc/lvmtab.d/* which are the database for all other lvm commands. SYNOPSIS
vgscan [-d|--debug] [-f|--forcenumbers] [-h|--help] [-r|--remove_snapshots [VolumeGroupName]] [-v|--verbose] DESCRIPTION
vgscan scans all SCSI, (E)IDE disks, multiple devices and a bunch of other disk devives in the system for volume groups defined. OPTIONS -d, --debug Enables additional debugging output (if compiled with DEBUG). -f, --forcenumbers If used volume group and/or logical volume minor numbers are found during scan, replace them. This will potentially cause problems for NFS exported filesystems on logical volumes with changed numbers. -h, --help Print a usage message on standard output and exit successfully. -r, --remove_snapshots [VolumeGroupName] Remove all snapshot logical volumes from all or just the named volume group. -v, --verbose Display verbose information of vgscan's activities. Hint Put vgscan in one of your system startup scripts. This gives you an actual logical volume manager database before activating all volume groups by doing a "vgchange -ay". DIAGNOSTICS
vgscan returns an exit code of 0 for success and > 0 for error: 1 error reading physical volumes 2 error inserting vokume group name into lvmtab 3 no volume group(s) found 4 error creating lvmtab 5 no or not enough free device specials to store volume group in lvmtab 6 error storing VGDA on disk(s) 7 reused LV device number 8 error releasing snapshot logical volume 95 driver/module not in kernel 96 invalid I/O protocol version 97 error locking logical volume manager 99 invalid command line See also lvm(8), vgcreate(8), vgchange(8) AUTHOR
Heinz Mauelshagen <Linux-LVM@Sistina.com> Heinz Mauelshagen LVM TOOLS VGSCAN(8)

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