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Full Discussion: Bad magic number on /dev/md0
Top Forums UNIX for Advanced & Expert Users Bad magic number on /dev/md0 Post 302132509 by ravinandan on Friday 17th of August 2007 07:56:08 AM
Old 08-17-2007
Bad magic number on /dev/md0

Hello All,
(RHEL4)
Few weeks ago I had posted a message in this forum about the problem I had when I replaced my two scsi disks and tried rebuild raid1 array.

I somehow managed to up the system with working raid1 array.
But the main problem persisted..
i.e when I reboot the system, mounting of /dev/md0 fails.
The error message says the superblock no. is wrong and it is expecting ext2 file system.

After this, I login in rescue mode(which the os provided me as soon as mount of /dev/md0 failed).

Once I login, I have to recreate the raid1 array using
mdadm --create /dev/md0 --level=raid1 --raid-devices=2 /dev/sdb1 /dev/sdc1

The above command successfully creates raid1 array after which I mount it to my /home directory.

Now everything works fine(until I restart)

(After full synchronization)
$cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sdc1[1] sdb1[0]
17782656 blocks [2/2] [UU]

unused devices: <none>

#mdadm -E /dev/sdb1
/dev/sdb1:
Magic : a92b4efc
Version : 00.90.00
UUID : 979caf2d:1be05876:14d74325:14ea3ec1
Creation Time : Fri Aug 10 15:47:52 2007
Raid Level : raid1
Device Size : 17782656 (16.96 GiB 18.21 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 0

Update Time : Fri Aug 17 17:11:05 2007
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Checksum : 14fdc667 - correct
Events : 0.92278


Number Major Minor RaidDevice State
this 0 8 17 0 active sync /dev/sdb1
0 0 8 17 0 active sync /dev/sdb1
1 1 8 33 1 active sync /dev/sdc1

# mdadm -E /dev/sdc1
/dev/sdc1:
Magic : a92b4efc
Version : 00.90.00
UUID : 979caf2d:1be05876:14d74325:14ea3ec1
Creation Time : Fri Aug 10 15:47:52 2007
Raid Level : raid1
Device Size : 17782656 (16.96 GiB 18.21 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 0

Update Time : Fri Aug 17 17:13:11 2007
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Checksum : 14fdc713 - correct
Events : 0.92292


Number Major Minor RaidDevice State
this 1 8 33 1 active sync /dev/sdc1
0 0 8 17 0 active sync /dev/sdb1
1 1 8 33 1 active sync /dev/sdc1

#cat /etc/mdadm.conf

DEVICE /dev/sdb1 /dev/sdc1
ARRAY /dev/md0 level=raid1 num-devices=2 UUID=979caf2d:1be05876:14d74325:14ea3ec1


#mdadm -E /dev/md0
mdadm: No super block found on /dev/md0 (Expected magic a92b4efc, got 764e5679)


Any help will be appreciated.
(Since I'm relieving from my current position I need to correct this problem...I don't want to pass this problem to my successor)

Regards,
Ravinandan S
 

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scsi-spin(8)						      System Manager's Manual						      scsi-spin(8)

NAME
scsi-spin - spin up and down a SCSI device SYNOPSIS
scsi-spin [-options...] [device] DESCRIPTION
scsi-spin let the user to manually spin up and down a SCSI device. This command is particularly useful if you've got noisy (or hot) drives in a machine that you rarely need to access. This is not the same as the kernel patch that's floating around that will automatically spin down the drive after some time. scsi-spin is completely manual, and spinning down a drive that's in use, especially the one containing the scsi-spin binary, is probably a really bad idea. To avoid running in trouble with such cases, scsi-spin verifies that the device to work on is not currently in use by scanning the mounted file system description file for a partition living on it and issue an error if this the case. OPTIONS
-u, --up spin up device. -d, --down spin down device. -e, --loej load or eject medium from drive (use along with -u or -d ) -w, --wait=[n] wait up to n seconds for the spin up/down command to complete. Default is to return immediately after the command was sent to the device. Either repeat -w n times or set n to define the time to wait before to report a timeout. -l, --lock prevent removal of medium from device. -L, --unlock allow removal of medium from device. -I, --oldioctl use legacy ioctl interface instead of SG_IO to dialog with device (could not be supported on all platforms). -e and -w are not allowed with this option. -v, --verbose=[n] verbose mode. Either repeat -v or set n accordingly to increase verbosity. 1 is verbose, 2 is debug (dump SCSI commands and Sense buffer). -f, --force force spinning up/down the device even if it is in use. -n, --noact do nothing but check if the device is in use. -p, --proc use /proc/mounts instead of /etc/mtab to determine if the device is in use or not. device the device is any name in the filesystem which points to a SCSI block device (sd, scd) or generic SCSI device (sg). See section below. SCSI devices naming convention Old kernel naming convention It is typically /dev/sd[a-z] , /dev/scd[0-9]* or /dev/sg[0-9]*. scsidev naming convention It is typically /dev/scsi/s[rdg]h[0-9]*-e????c?i?l? or /dev/scsi/<aliasname>. devfs naming convention It is typically /dev/scsi/host[0-9]/bus[0-9]/target[0-9]/lun[0-9]/disc (same for cd and generic devices) or short name /dev/sd/c[0-9]b[0-9]t[0-9]u[0-9] when devfsd "new compatibility entries" naming scheme is enabled. SEE ALSO
scsiinfo(8), sg_start(8), sd(4), proc(5), AUTHORS
Eric Delaunay <delaunay@debian.org>, 2001 Rob Browning <rlb@cs.utexas.edu>, 1998 03 September 2001 scsi-spin(8)
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