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/dev/md strangeness with raid10. Panic can't mount root
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clytle374
Apprentice
Apprentice


Joined: 01 Aug 2006
Posts: 166

PostPosted: Mon Sep 06, 2010 5:30 pm    Post subject: /dev/md strangeness with raid10. Panic can't mount root Reply with quote

After a year with Ubuntu, I'm back. I've had Gentoo on this machine before with a raid0 setup, it's an amd64 system with 3 sata drives. I did it differently this time and used raid10 for redundancy and ext4, both are built into the kernel and not modules. The array is 3 disks on /dev/sdX and there is another disk /dev/hda for windows.

I followed http://www.gentoo.org/doc/en/gentoo-x86+raid+lvm2-quickinstall.xml and this http://www.gentoo.org/doc/en/handbook/handbook-amd64.xml as always.

I did the usual
Code:
mknod /dev/md0 b 9 0
 mdadm --create /dev/md0 --level=10 --raid-devices=3 --metadata=0.90 /dev/sda3 /dev/sdb2 /dev/sdc2 


set grub and fstab to use /dev/md0

upon reboot I get the unable to mount root. So I boot back into the minimal usb stick and can't assemble the array, upon doing in fdisk -l I realize that my array is now /dev/md127 :?

Code:
fdisk -l

Disk /dev/hda: 40.0 GB, 40020664320 bytes
16 heads, 63 sectors/track, 77545 cylinders
Units = cylinders of 1008 * 512 = 516096 bytes
Disk identifier: 0x9cf23ab1

   Device Boot      Start         End      Blocks   Id  System
/dev/hda1   *           1       65775    33150568+   7  HPFS/NTFS
Partition 1 does not end on cylinder boundary.
/dev/hda2           65776       76755     5533920    7  HPFS/NTFS
Partition 2 does not end on cylinder boundary.
/dev/hda3           76756       77536      393592+  83  Linux
Partition 3 does not end on cylinder boundary.

Disk /dev/sda: 80.0 GB, 80026361856 bytes
255 heads, 63 sectors/track, 9729 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x1cbf4bb6

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1          20      160618+  83  Linux
/dev/sda2              21         129      875542+  82  Linux swap / Solaris
/dev/sda3             130        9729    77112000   fd  Linux raid autodetect
/dev/sda4   *           1           1           0    0  Empty
Partition 4 does not end on cylinder boundary.

Disk /dev/sdb: 80.0 GB, 80026361856 bytes
255 heads, 63 sectors/track, 9729 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x000ccec4

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1         128     1028128+  82  Linux swap / Solaris
/dev/sdb2             129        9729    77120032+  fd  Linux raid autodetect

Disk /dev/sdc: 80.0 GB, 80026361856 bytes
255 heads, 63 sectors/track, 9729 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00060f36

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1               1         128     1028128+  82  Linux swap / Solaris
/dev/sdc2             129        9729    77120032+  fd  Linux raid autodetect

Disk /dev/sdd: 2029 MB, 2029518848 bytes
63 heads, 62 sectors/track, 1014 cylinders
Units = cylinders of 3906 * 512 = 1999872 bytes
Disk identifier: 0x00000000

   Device Boot      Start         End      Blocks   Id  System
/dev/sdd1   *           1        1014     1980311    c  W95 FAT32 (LBA)

Disk /dev/md127: 118.4 GB, 118443933696 bytes
2 heads, 4 sectors/track, 28916976 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Disk identifier: 0x00000000

Disk /dev/md127 doesn't contain a valid partition table


So I update grub and fstab to reflect / being on /dev/md127 and get the same error.

More or less it is this
Code:

VFS: Cannot open root device "md127" or unknown-block(2,0)
Please append a correct "root=" boot option; here are the available partitions:
800 sda driver: sd
801 sda1
802 sda2
803 sda3
sr0 driver: sr
Kernel Panic - not syncing: VFS Unable to mount root fs on unknown-block(2,0)


At least I can chroot back into the system.
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DONAHUE
Watchman
Watchman


Joined: 09 Dec 2006
Posts: 6253
Location: Goose Creek SC

PostPosted: Mon Sep 06, 2010 6:22 pm    Post subject: Reply with quote

Presuming a current kernel and a current udev and a deprecated kernel config; you may be a victim of udev ceasing to support the deprecated legacy hard drive adapter drivers. If running:
boot the cd, mount the gentoo partition(s),
Code:
grep -i config.ide /mnt/grntoo/usr/src/linux/.config
grep -i config_ata /mnt/grntoo/usr/src/linux/.config
yields
Quote:
CONFIG_IDE=y
#CONFIG_ATA is not set

your kernel is using the deprecated drivers.
If both =y driver confusion may exist.
Discussion
If on legacy drivers an update is highly recommended. Note that any hda reference in /etc/fstab and /boot/grub/grub.conf will need to change to sd?, depending on how the drives are re-enumerated.
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