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Old 05-15-2008, 02:29 PM   #1
kushalkoolwal
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Transition to libata driver - SCSI system - GRUB changes


My Specs:
Debian 4.0
2.6.25
GNOME/GDM/Xorg

Recently I moved to using the libata driver (in Kernel) for my IDE devices which caused my entire system to move to SCSI system. Basically all instances of "/dev/hd*" should be now referred to as "/dev/sd*". I changed those in my GRUB (menu.lst) file and in my /etc/fstab. All was fine until I thought of this scenario:


Suppose my Debian system is installed on Primary Slave (/dev/sdb) with a another hard drive as my primary master (/dev/sda). Now what if I just remove my primary master and just boot the system? My system won't boot because my GRUB still refers to "root=/dev/sdb1" which is no longer valid because with just one disk present it will be treated as /dev/sda by linux Kernel under the new SCSI system. I will have to change the line in GRUB to "root=/dev/sda1".

Is there is a workaround for this? I have seen that new releases of UBUNTU using root=UUID=<some large number>. Is that the solution?

Any help will be greatly appreciated.


Thanks
 
Old 05-16-2008, 08:16 AM   #2
syg00
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Ignore this ... too late at night
 
Old 05-16-2008, 12:25 PM   #3
kushalkoolwal
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Quote:
Originally Posted by syg00 View Post
Ignore this ... too late at night

Not quite sure as to what you are trying to say. Should I ignore the SCSI system or you are going to reply once you get up in the morning?
 
Old 05-16-2008, 02:54 PM   #4
mostlyharmless
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I would just add a new line to grub as you suggested (prior to taking out the primary master) and label it in grub as "alternate boot with primary master missing" or something; using the UUID should work too, though I haven't tried it.
 
Old 05-16-2008, 04:35 PM   #5
kushalkoolwal
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Originally Posted by mostlyharmless View Post
I would just add a new line to grub as you suggested (prior to taking out the primary master) and label it in grub as "alternate boot with primary master missing" or something; using the UUID should work too, though I haven't tried it.

Hmm. Does it mean that it is a shortcoming of SCSI system? Because with the /dev/hd* thing those would never change even if you remove/add a drive or a CD-ROM.....
 
Old 05-16-2008, 09:26 PM   #6
syg00
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The problem isn't libata per se, but probably the initscripts - and udev rules.
You should be able to use /dev/disk/by-id/... I'd imagine. Not sure if that will be available by the time you want to mount the root or not.
Easy enough to test.

I find UUID to be a PITA - you'll have to add support for it in an initrd to use it for grub parms. I guess with Debian you're already using an initrd - I never do when I build a kernel.
Also UUIDs aren't necessarily unique. Try dd'ing a few partitions around ...

If I find I can't boot a system because of a disk "moving", I just adjust the grub entry from the menu, and fix it (permanently) later. LABELs (or UUID) in the fstab will get you around those mountpoints now being on a different device.
 
Old 05-17-2008, 02:54 PM   #7
kushalkoolwal
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Quote:
Originally Posted by syg00 View Post
The problem isn't libata per se, but probably the initscripts - and udev rules.
You should be able to use /dev/disk/by-id/... I'd imagine. Not sure if that will be available by the time you want to mount the root or not.
Easy enough to test.

I find UUID to be a PITA - you'll have to add support for it in an initrd to use it for grub parms. I guess with Debian you're already using an initrd - I never do when I build a kernel.
Also UUIDs aren't necessarily unique. Try dd'ing a few partitions around ...

If I find I can't boot a system because of a disk "moving", I just adjust the grub entry from the menu, and fix it (permanently) later. LABELs (or UUID) in the fstab will get you around those mountpoints now being on a different device.
I see....Thanks for the explanations. So basically it is the udev and init-scripts which names the devices as sd* when they see libata driver being loaded?
 
  


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