[lug] Musical Device IDs?

[Zan Lynx]

On Mon, 2007-01-29 at 15:13 -0700, David Morris wrote:
> Ok, this is driving me crazy.
> 
> I have a system running Debian Etch (testing) with the
> 2.6.18 kernel.  AMD64 architecture.  In this system I have
> an SATA controller with 1 (boot) hard disk, a SCSI
> controller with 2 hard disks and an external CompactFlash
> USB drive.  All very standard stuff.
> 
> The problem arises when I boot the system.  The three
> controllers (SATA, SCSI, and USB) play musical chairs with
> their device IDs.  Here is my "nominal" mapping:
> 
> /dev/sda    SATA hard disk (boot disk)
> /dev/sdb    SCSI hard disk #1
> /dev/sdc    SCSI hard disk #2
> /dev/sdd    USB CompactFlash Drive
> 
> When the system boots up, the SATA hard drive may end up
> being sda, sdb, sdc, *or* sdd.  Sometimes it decides to mess
> with my mind and make me reboot the system a dozen times
> before the SATA hard drive lands on /dev/sda.
> 
> Any ideas on how to put a stop to this insanity before I
> strangle the system?

Do not mount by drive letter.  Here's a sample of my /etc/fstab from my
laptop.  I'm using udev.

/dev/disk/by-uuid/eeca71d7-e22f-48e6-b500-48dca49d20a4 /boot            reiserfs        defaults,noatime,nodiratime,notail 1 1
/dev/disk/by-uuid/b35cd254-b64b-4432-b882-f4bdb0c36498 /                reiser4         defaults,noatime,nodiratime 1 1
/dev/disk/by-uuid/fd35277a-8dc7-4afe-8257-fda61b757344 none             swap            sw             0 0

/dev/disk/by-label/Backup  /media/Backup  reiserfs      defaults,noatime,nodiratime,noexec,nodev,user 0 0
/dev/disk/by-label/Backup2 /media/Backup2 reiserfs      defaults,noatime,nodiratime,noexec,nodev,user 0 0

The newer kernels are using hotplug dynamic device discovery, and adding
multi-threaded bus probing in the future.  Might as well bite the bullet
and accept that drive letters will never be the same again.

Instead of UUID and labels like I used, you could also use
udev's /dev/disk/by-path, where you can specify drives by the
controller's PCI bus ID, SCSI ID, and partition number.  That's a bit
more Solarisey if you like that.
-- 
Zan Lynx <zlynx at acm.org>
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