UUIDs on drives

[ghe]

Mario Vukelic wrote:

> "Used to" being the instrumental expression.

Yup. Worked at point A, didn't at point B. A popular description for 
that condition is "broken".

> Yes, that was back then. As I understand it, now that we have SATA and
> whatnot, this is simply not guaranteed by the hardware anymore.

Nope. The hardware has *got* to be consistent in its self description. 
Otherwise the OS's be writing to disk locations at random.

On my machine, there are 4 places to plug in SATA disks, and 32 possible 
  locations on the SCSI bus. Number 1 SATA connector is number one SATA 
connector always and forever. It's called sda when there's nothing found 
on the SCSI bus. If there's a SCSI disk, that becomes sda, and SATA 
connector number one becomes sdb -- it's the software that labels them, 
the software is written by humans, and they can have it label the number 
one SATA connector with a random number generator or not, it's up to them.

> But you can still tell grub from which partition to boot.

Yes, but that's not a lot of help when it's trying to read that 
partition on the wrong disk. Or when you can't get to menu.lst to 
correct the problem

> It's not that somebody came up with the idea to rename things just for
> the heck of it. The kernel developers decided that all these devices
> should be handled by the SCSI subsystem. 

That's a wonderful idea. But the labels in /dev are nothing but text 
tags pointing to the real stuff. st.. would have worked. So would sD... 
or Sd.

> It's certainly possible to
> disagree with this decision, but someone dong so should be prepared to
> take it up with the kernel developers on their level.

I did. They told me, essentially, "My way or Windows." I'm on their way, 
but whining...

>> so when I installed Heron on my Mac Pro the other day, then
>> turned on an external SCSI disk, then updated Ubuntu's kernel, I got to
>> reinstall Ubuntu.
> 
> Huh?

After the install, all was well; the number one SATA was sda. Then I 
turned on the SCSI disk and rebooted -- now the SCSI disk was labeled 
sda, instead of the SATA. Then Ubuntu updated the kernel, and part of 
that involves rewriting parts of /boot/grub/menu.lst; and when it did 
that, the system wouldn't boot anymore -- I think it wrote the boot 
block on the SCSI disk. I don't know for sure, but it wouldn't boot into 
Linux.

OTOH, this is a very peculiar environment. There *is* no BIOS on the 
Mac, so I had to jump through a couple hoops to get Ubuntu to realize 
that and not try to use it.

> I'm attaching external disks all the time and I never had this problem,
> so I don't know what the problem here would be. Why _reinstall_?

Simply because the kernel update scribbled on some info necessary to 
find the OS at boot time. If I hadn't updated the kernel with the SCSI 
disk on, it would have been OK. I think.

But that's just this case. I've been fighting with the mixture of BIOS 
fluctuations and udev on my mixed SCSI/SATA servers for a very long time 
now -- usually I just find something that works and leave it alone and 
hope nothing ever goes wrong. So far, so good. But it's not a long-term 
solution...

-- 
Glenn English
ghe at slsware.com