UUIDs on drives
ghe
ghe at slsware.com
Thu Aug 14 22:52:39 UTC 2008
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
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