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Re: Persistent device names

On Wed, May 17, 2006 at 01:00:45AM +0200, Frans Pop wrote:
To discuss this subject, I've still wanted to set up a discussion with at least Marco, you, Joey and Colin, but for different reasons have not gotten around to that.

As I'll be on holiday for a few weeks after Debconf, let me at least list the issues that I've had in mind and that should be considered when implementing changes for persistent device naming.
Please add to the list and comment.

- We should like to keep support for devfs and regular device names in
 the installer; loosing that would mean no support for 2.2/2.4 installs
 (although those are likely to be dropped anyway) and no support for
 installs of Sarge and I think may be a problem for debian-edu.
 However, if it is unavoidable, we could drop this requirement.

But do 2.4 and 2.2 not use traditional device names after booting into the installed system?

- Are there likely to be architecture specific issues with persistent
 device naming?
- Or with filesystems other than ext2/ext3?

- Persistent device naming is mostly needed to get rid of errors on
 reboot. Most common case is where a system has multiple disk
 controllers and the order in which their drivers are loaded is
 different after the reboot than in d-i leading to a different order
 in device names.

Yes, and it would also help with upcoming issues. For instance, the 2.6 kernels seem to move towards supporting ordinary (PATA) IDE via libata, meaning that hdaX devices would also become sdaX in the future. With persistent names this wouldn't be a problem.

In addition, persistent names could be good for complex cases like root-on-lvm-on-crypto-on-md-on-disks.

I've been considering whether it would be a good idea to introduce a new parameter (for initramfs-tools/yaird) specifying a comma-separated list of all devices needed to bring up the root dev. Something along the lines of rootdeps=/dev/sda1,/dev/sda2,/dev/mapper/mainvg-rootlv.

Then the initramfs/initrd could do its best to bring up all those devices before trying to mount root via the persistent device. This would help with the complex scenarios...

It wouldn't help with grub/lilo/etc though.


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