linux-kernel - Re: Linix-3.6.3 sda, sdb drives in reverse order (with a USB 2.0 drives and a monolithic kernel configuration)

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Date:	Sat, 27 Oct 2012 01:57:54 +0200
From:	Wallak <wallak@...e.fr>
To:	Chris Friesen <chris.friesen@...band.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Linix-3.6.3 sda, sdb drives in reverse order (with a USB 2.0
 drives and a monolithic kernel configuration)

Chris Friesen wrote:
> On 10/26/2012 01:43 PM, Wallak wrote:
>> Chris Friesen wrote:
>>> On 10/25/2012 04:49 PM, Wallak wrote:
>>>> I've a very annoying behavior with the linux-3.6.x kernels release, 
>>>> and
>>>> a monolithic configuration. The USB 2.0 drives are mapped first with
>>>> /dev/sda, /dev/sdb... devices, and than the SATA AHCI drives come 
>>>> after.
>>>> This is out of order with the BIOS configuration and breaks a program
>>>> like lilo. This is also annoying when we use a static partition 
>>>> mapping.
>>>>
>>>> Linux-3.5 works fine. Where this bug come from ? Is this a patch to 
>>>> get
>>>> the old, and classical behavior ?
>>>
>>> As you have discovered it's fragile to rely on /dev/sd* names since a
>>> BIOS update, kernel update, or motherboard replacement could
>>> conceivably cause them to change.
>>>
>>> Better to use something like partition labels that you control and
>>> that don't change.
>>>
>>> Chris
>>>
>> You are right, when we have a configuration with a lot of drvies and
>> adapters SATA, old SCSI,.. etc. the order may change. But having the
>> main SATA hard drive defined, as the BIOS boot device, behind external
>> and removable USB drives is in my opinion a bug.And may lead to security
>> issues (drives with the same label, etc...).
>>
>> Using =LABEL, or =UUID with a bootloader like grub or lilo, save the the
>> boot device mapped drive partition number , and so booting on an older
>> kernel like linux 3.5 will fail. If we remove the external USB drive,
>> the boot process will fail too...
>>
>> So such a bug have to be fix.
>
> If you specify "root=LABEL=<label>" as part of the kernel boot args in 
> grub does it not check the label at boot time?

Using root=LABEL= or root=UUID= don't work on a plain kernel, this 
feature may be handled by an initrd trick. Otherwise for all non root 
partitions UUID= work fine.
Nevertheless not fixing this bug yields some other issues:  Using lilo 
to launch a second OS (other= option) fail, the command try to parse 
partitions available on /dev/sda, and miss the real main HDD. Boot drive 
must be force with lilo options...
SATA drives have, most of the time, no reason to be behind USB drives. 
If we want to get a reliable behavior: /dev/sda must be mapped to the 
BIOS boot device. Using the same behavior as linux-3.5 will be fine.

Wallak.

>
> Chris
>

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