[ale] RAID mirror boot nightmare

Bob Toxen transam at VerySecureLinux.com
Tue Jul 10 01:33:32 EDT 2012


Additional details on this miserable problem:

On Boot the kernel complains of:

  Creating root device
  Mounting root filesystem
  Mount: Could not find filesystem '/dev/root'

after talking about md0 apparently being created successful and lastly
panics.

/boot/grub/grub.conf entry  being booted:
title CentOS-single-md4
	root (hd0,0)
	kernel /vmlinuz-2.6.18-308.4.1.el5 ro root=/dev/md4 md=4,/dev/sda6,/dev/sdb6 md=1,/dev/sda2,/dev/sdb2 md-mod.start_dirty_degraded=1 rhgb single noresume
	initrd /initrd-2.6.18-308.4.1.el5.img

/etc/mdadm.conf (heavily edited by me including switching from uuid to
devices; I don't presently list swap as that is not critical and it
fails before even thinking about swap):
# mdadm.conf written out by anaconda
DEVICE /dev/sda[26] /dev/sdb[26]
MAILADDR root
ARRAY /dev/md4 level=raid1 num-devices=2 devices=/dev/sda6,/dev/sdb6 auto=yes
ARRAY /dev/md1 level=raid1 num-devices=2 devices=/dev/sda2,/dev/sdb2 auto=yes

fdisk output:
Disk /dev/sda: 1000.2 GB, 1000204886016 bytes
255 heads, 63 sectors/track, 121601 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          13      104391   83  Linux
/dev/sda2   *          14          26      104422+  fd  Linux raid autodetect
/dev/sda3              27        4200    33527655   82  Linux swap / Solaris
/dev/sda4            4201      121601   943023532+   f  W95 Ext'd (LBA)
/dev/sda5            4201       62900   471507718+  83  Linux
/dev/sda6           62901      121600   471507718+  fd  Linux raid autodetect

/etc/fstab:
/dev/md4        /                       ext3    defaults        1 2
/dev/md1        /boot                   ext3    defaults        1 2

#normal /dev/md3        /                       ext3    defaults        1 1
#normal /dev/md0        /boot                   ext3    defaults        1 2
#normal /dev/md4        /root2                  ext3    defaults        1 2
#normal /dev/md1        /boot2                  ext3    defaults        1 2
tmpfs                   /dev/shm                tmpfs   defaults        0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc    defaults        0 0
/dev/md2                swap                    swap    defaults        0 0


What magic am I missing?  Please help!!!

Bob

On Mon, Jul 09, 2012 at 06:21:43PM -0400, Bob Toxen wrote:
> I'm having problems getting my RAID mirror booting again in
> CentOS 5.8 64-bit after GNU's gparted trashed my partition table when
> one of the new Seagate 1 TB SATA disks failed completely.
> 
> Booting causes the kernel to complain of an invalid root partition.
> I can't figure out what is invalid about it.  FSCK is happy.
> 
> I rebuilt the partition table with "CD Rescue" v2.7.1 bootable CD
> (wonderful stuff) and reinstalled my existing GRUB to the MBR.
> 
> 
> Unfortunately, CentOS 5.8 will no longer recognize my md3 root partition
> (still running in degrated mode since I've not yet replaced the failed
> disk).  The CentOS kernel does see the RAID partitions but just doesn't
> want to use one for /!!!
> 
> I CAN boot the "CD Rescue" disk and tell it to find and boot an
> existing OS on the hard disk and it will bring up my CentOS 5.8 on
> md3 (before I did mdadm -S /dev/md3 and used fdisk to change its
> partition type from RAID to Linux)
> or will boot up md4 (though apparently with a newer 3.x kernel from the CD).
> 
> However, no matter what I do I cannot get my CentOS 5.8 to boot the RAID
> mirror.  I also have the root and /boot file systems duplicated to
> md4 and md1 respectively.
> 
> I tried
> 
>   mdadm -S /dev/md3
>   mdadm -S /dev/md1
>   mdadm --create -n 2 /dev/md3 --level=mirror /dev/sda6 missing
>     "/dev/sd6 appears to be part of an existing RAID; do anyway" y
>   mdadm --create -n 2 /dev/md1 --level=mirror /dev/sda2 missing
>     "/dev/sd2 appears to be part of an existing RAID; do anyway" y
> 
> but when I try to boot CentOS 5.8 with "root-md3" it again fails.
> 
> However, booting the CD Rescue and selecting "find and boot from hard
> disk" happily boots either RAID partition.
> 
> 
> Please PLEASE give me some ideas to fix this.  $50 to the first right
> answer, REALLY!  I'm desperate.
> 
> Nothing on the file systems themselves, including  the /boot/initrd*
> file and kernels, appear to be damaged.  systems themselves)
> 
> 
> Since FSCK is happy all I can think of is damage to the md superblock at
> the end of the physical partitions.  I wonder if the CD Rescue kernel
> (being newer than the CentOS kernel) created to new a version of the
> mdsuperblock.  However, my recreating the RAID mirror under CentOS 5.8
> should have fixed it, shouldn't it?
> 
> HELP!  $50 prize.  Really!
> 
> Bob Toxen
> bob at VerySecureLinux.com
> transam at VerySecureLinux.com
> 404-216-5100 Cell (except for the next half hour)
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