IDE/SATA disks switch places after kernel boots

ISHAIM

Hello,

I have a hardware setup in which I'm trying to set up grub dual boot between an IDE hard drive containing Gentoo and a SATA hard drive containing Windows. I have the option in my BIOS to set the boot priority of connected hard drives. I have set this option to the IDE/Gentoo hard drive as the first priority, which is how I'm able to get to grub in the first place.

Before the kernel continues the boot process, grub can detect that the IDE hard drive is indeed (hd0,0). However, once control is handed off to the kernel, there is a kernel panic, and I can see from the output (wish I had a more elegant/proper name for this) that /dev/sda and /dev/sdb have switched places, judging from their partitions which is also displayed in the output.

From what I'm Googling, I may need to utilize the initramfs guide at http://www.gentoo.org/doc/en/initramfs-guide.xml, but I am uncertain whether this would be the proper solution or not.

I would just like to be sure of this in case I am wrong, and/or any additional advice. Thank you for your time.

cal22cal · n00b Joined: 19 Jan 2006 Posts: 36

I would suggest using the initramfs and load the ide driver as module.
https://forums.gentoo.org/viewtopic-t-474514.html

VoidMage · Watchman Joined: 14 Oct 2006 Posts: 6196

If the drives are gpt partitioned, booting by PARTUUID would be a solution.

_______0 · Guru Joined: 15 Oct 2012 Posts: 521

use

ISHAIM · Posted: Fri Jan 11, 2013 3:16 pm Post subject:

VoidMage · Watchman Joined: 14 Oct 2006 Posts: 6196

uuid reported by blkid and PARTUUID on gpt partitioned disks are different things.

ISHAIM · Posted: Fri Jan 11, 2013 9:06 pm Post subject:

Okay, then am I correct in assuming they are -nearly- the same? Perhaps I am not being specific enough? In a PARTUUID implementation on gpt partitioned disks, wouldn't you still use the UUID reported by blkid? I am trying to make sure I understand this correctly as that is the impression I get from reading http://wiki.debian.org/Part-UUID.

VoidMage · Watchman Joined: 14 Oct 2006 Posts: 6196

Those numbers are independent.
IIRC, you can check PARTUUID either by gptfdisk or 'udevadm info' on the partition.

ISHAIM · Posted: Sun Jan 13, 2013 5:37 am Post subject:

VoidMage, I still fail to understand what you mean or are getting at. udevadm info --query=all --name=/dev/sda3 returns several lines, one being

VoidMage · Watchman Joined: 14 Oct 2006 Posts: 6196

In such case, your disk is most likely not gpt-partitioned. Otherwise it would have 'by-partuuid' symlink and ID_PART_ENTRY_UUID .

NeddySeagoon · Posted: Sun Jan 13, 2013 9:29 pm Post subject:

ISHAIM,

The key difference is that with GPT partitioned disks, you do not need an initrd to boot using PARTUUID.

The PARTUUID is a property of the partition, the UUID mostly discussed here is the UUID of the filesystem.
DOS Partitions do not have a PARTUUID property.

On a GPT disk, the PARTUUID is created at the time the partition is created. Unlike the filesystem UUID, it is not changed if you reformat the partition.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

gkmac · Posted: Sun Jan 13, 2013 9:44 pm Post subject:

ISHAIM · Posted: Mon Jan 14, 2013 3:51 pm Post subject:

I'm going to assume my IDE Linux drive is MBR since fdisk doesn't support GPT. That being said, I'm also assuming that means in order to dual boot with 2 physically separate Windows/Linux disks, I will need to use initramfs to stop sda and sdb from switching places once the kernel picks up the boot process from GRUB.

The problem I see is that, according to cal22cal, I should compile the IDE driver as a module, which genkernel doesn't support according to http://www.gentoo.org/doc/en/initramfs-guide.xml, so I'll probably follow the guide at http://en.gentoo-wiki.com/wiki/Initramfs.

I wish there were a way to be sure that initramfs will indeed stop sda and sdb from switching, before doing all the work, although I'm assuming that is how it will work.

NeddySeagoon · Posted: Mon Jan 14, 2013 4:23 pm Post subject:

ISHAIM,

With an initramfs (initrd) the kernel partition names need not be used. The initrd contains the userspace tool mount and mount understands filesystem UUIDs.

You use blkid to discover your UUIDs, then in grub you can write root=UUID=<UUID_of_root_filesystem>
You also use UUIDs in /etc/fstab.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

krinn · Watchman Joined: 02 May 2003 Posts: 7471

Because noone told the simplicity answer, here's the "easy" solve.

Put your pata drivers build-in kernel (something that should be already done), and set your sata driver as module, this way when kernel load the sata driver, drives letters are already assign to the drives attach to the pata controller.
Except if you use a driver that handle both controllers, this will works.

NeddySeagoon · Posted: Mon Jan 14, 2013 8:41 pm Post subject:

krinn,

Tell why too ...
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

krinn · Watchman Joined: 02 May 2003 Posts: 7471

well, easy, first controller load, first disks attach to it get a number.

So loading a controller driver as module will be loaded after any controller buildin kernel.

It's now easy to see the logic

- builin PATA : assigning drive letters : sda to sdX for all drives attach to it
- then loading sata module drivers : assigning what drives letters it could but cannot retake ones already taken : sdX to end so

And this is why it cannot work if you don't have two controllers or a driver that handle both controller.

NeddySeagoon · Posted: Tue Jan 15, 2013 7:05 pm Post subject:

krinn,

10/10 ... as expected :)
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

krinn · Watchman Joined: 02 May 2003 Posts: 7471

It's warming to get a 10/10, but from you, you can't imagine how proud & happy i'm now.

Thank you neddyseagoon

s4e8 · Guru Joined: 29 Jul 2006 Posts: 311

since 3.8-rc1 kernel, PARTUUID recognize trandictional fdisk partitions too. The format is PARTUUID=XXYYZZTT-PP, XXYYZZTT is MBR signature at byte 1bb,1ba,1b9,1b8, the PP is partition number.