Linux – After a yum update, physical drives sda and sdb are swapped and sdc is missing

fstablinux

yum update installed kernel 2.6.32-504.8.1-el6.x86_64, and was correctly installed to /dev/sdb1/boot (ext3).

Physical drives on the machine (with expected/normal/previous device labels):

 /dev/sdb1,   ext3, 70 MB
 /dev/sda has three:
      sda1    ext3, 42 MB
      sda2    ext4, VolGroup00, 1TB LVM
      sda3    unallocated, 7 MB
 /dev/sdc1,     ext3  2 TB

/etc/fstab looks like:

/dev/mapper/VolGroup00-root    /      ext4
/dev/sdb1                      /boot  ext3
/dev/sdc1                      /data  ext3

Now, for the problem description:

After a reboot, sda becomes sdb and sdb becomes sda, and sdc is MIA (cfdisk, fdisk and gparted report no such device). Needless to say, I haven't dis-/connected any additional devices.

Can someone make a suggestion as to what happened? This is behaviour I would expect after drive cables were moved around, or a new device were connected.

My only guess is the sdc drive has failed (since it doesn't appear in dmesg), however since it's after and sda and sdb, why would those two drives be re-ordered?

Additional details/background: Dell R2970, CentOS 5, last reboot ~March 19 perfectly normal, not sure if kernel was updated then, but probably as that is the only reason this machine would have been reboot.

Best Answer

Look at the /etc/udev/rules.d/ or similar location for udev. They contain static rules for your devices which have been recognized and stored (drives, net etc.). Some OSes (or distros) have the lack of this functionality.

In rare cases, for example, changing the udev structure or file structure, the information can be reset. And you will have mess of drives.

Do NOT rely on /dev/sd* names. Never ever on the server environment.

Always DO rely /dev/disk/by-uuid/ names because they don't change. Change any links (at bootloader, kernel startup etc.) for UUIDs.

Actions: reinstall bootloader, update configs, update initrd.

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