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Old 10-04-2008, 02:18 PM
"Thomas H. George"
 
Default disk names at boot

Regarding disk names see my posting "Re: grub with sata drives -
solution"


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Old 11-03-2008, 03:40 PM
ghe
 
Default disk names at boot

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I have servers with a SCSI disk for the system and a RAID1 of SATAs for
data. That's what I want, anyway.

What I want to happen is the SCSI disk should always be sda, the SATAs
should be sdb & c, anything IDE should be called hd<something>, and
externals should be just about anything else. I can get the BIOS to make
the SCSI be hd0 when grub takes over.

When the SCSI is the only drive in the box, it's called sda when grub
wants to load the kernel, and it's still sda when mount reads fstab. But
if there are SATAs in there, the SCSI is sdc; menu.lst is wrong, and so
is fstab.

I could handle that by editing a couple files. But if one or more of the
SATAs dies, the whole system would be broken. Besides, I'd like to
knowing what sda is when I go to use dd...

And if a USB drive is plugged in at boot time, everything is broken.

I've spent hours googling, RTFM'ing, writing udev rules, and even trying
to understand some source code. But I can't get things to be the way I
want. I'm beginning to thing I'm missing something.

I can't find anything that tells just what's happening in the boot
process (Debian lenny, amd64). It seems that udev is doing something
just before the boot menu is displayed (rules involving FS keys cause a
long pause; rules with only KERNEL keys don't). But I can't find out
what it's doing, and my rules don't seem to change the names.

I have no trouble getting udev to name the USB stick "sdu" with a
symlink "usb_stick" after the system is thoroughly booted.

I can post some of my rule attempts, if that'd help, but they're on the
machine in the other room...

Does it even have anything to do with udev? Or is it the order the buses
are examined by something? If so, how can I control this order?

Or am I looking at the wrong things completely?

- --
Glenn English
ghe@slsware.com

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Old 11-03-2008, 06:05 PM
ghe
 
Default disk names at boot

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David Schmidt wrote:

> I might be wrong but perhaps e2label is what you are looking for.

Been there; done that :-)

That would work to get the machine booted, as would using the UUIDs. But
I really want my system disk to be sda so the /dev filesystem will work
as expected with tools like dd. (I almost scribbled all over the wrong
disk once because of this.)

Time was that sd<n> meant SCSI disk as numbered by addresses on the SCSI
bus, and hd<n> was selectable by controller / master / slave, and the
USB stuff was off over there. I realize there's a significant problem
with major / minor numbers and the size of /dev, but I'm not completely
happy with the kernel folks' solution -- it breaks too much stuff...

- --
Glenn English
ghe@slsware.com

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Old 11-03-2008, 06:48 PM
Florian Kulzer
 
Default disk names at boot

On Mon, Nov 03, 2008 at 12:05:26 -0700, ghe wrote:
> David Schmidt wrote:
>
> > I might be wrong but perhaps e2label is what you are looking for.
>
> Been there; done that :-)
>
> That would work to get the machine booted, as would using the UUIDs. But
> I really want my system disk to be sda so the /dev filesystem will work
> as expected with tools like dd. (I almost scribbled all over the wrong
> disk once because of this.)

I think you can use the device node symlinks in /dev/disk/by-label/ or
/dev/disk/by-uuid/ to avoid ambiguities, or you can write your own udev
rules to generate other symlinks in /dev that always point to the right
partitions.

AFAIK, the present architecture of the Linux kernel does not allow for
the /dev/sdX nodes themselves to be well-defined in the manner that you
would prefer.

--
Regards, | http://users.icfo.es/Florian.Kulzer
Florian |


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Old 11-03-2008, 09:11 PM
ghe
 
Default disk names at boot

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Florian Kulzer wrote:

> I think you can use the device node symlinks in /dev/disk/by-label/ or
> /dev/disk/by-uuid/ to avoid ambiguities, or you can write your own udev
> rules to generate other symlinks in /dev that always point to the right
> partitions.
>
> AFAIK, the present architecture of the Linux kernel does not allow for
> the /dev/sdX nodes themselves to be well-defined in the manner that you
> would prefer.

You may be right. The sd?? Nazis may have broken the kernel :-)

Now I'm investigating building a customized initrd -- I'm beginning to
think that's where the names are set for the disks available at boot
time, and forever after. It looks like it may be possible to do what I
want by controlling that kernel's module load order. Unless it's the
same, single module that scans both SCSI and SATA controllers. In which
case it'd take, best case, some source code editing: far too much trouble.

I have a hard time believing, though, that there wouldn't have been a
lot of very loud wailing if it's not possible for us old server admins
to set things up the way I want to...

- --
Glenn English
ghe@slsware.com

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Old 11-04-2008, 06:13 AM
NN_il_Confusionario
 
Default disk names at boot

On Mon, Nov 03, 2008 at 03:11:38PM -0700, ghe wrote:
> I have a hard time believing, though, that there wouldn't have been a
> lot of very loud wailing if it's not possible for us old server admins
> to set things up the way I want to...

No warranties, but:

* you can try a system where udev is NOT even installed (almost all my
systems, and all systems which I have personally installed, are of this
kind. The few remaining ones are covered by the next point).

This requires a self-complied kernel without initrd, or a debian stock
kernel where the initrd is build by yaird. Note that at this time yaird
from sid works also on etch (fetch the package, dpkg --force-depends -i,
then manually adjust in /var/lib/dpkg/status the Depends: line for
yaird; it will work also with etch libc6)

* you can try a system where udev is installed but does NOT start
neither from the initrd or at boot (use rcconf, or edit symlinks in rc.d
directories or the file /etc/rc.conf fir file-rc is installed, or
whatever). Almost the same as above.

* you can try a system where udev is installed and starts at boot (but
NOT from the initrd), but in udev.conf a directory different from /dev/
is specified. See /usr/share/doc/udev/ search for something like
"disabling udev". The difference with the previous points is that udev
still loads modules.

In my opinion, udev is pretty useless on a machine where hardware does
not change and manual loading from /etc/modules in the order you want
permits avoiding tampering with udev rules.

No warranties (even if I am VERY happy with the udev - free machines).

--
Chi usa software non libero avvelena anche te. Digli di smettere.
Informatica=arsenico: minime dosi in rari casi patologici, altrimenti letale.
Informatica=bomba: intelligente solo per gli stupidi che ci credono.


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Old 11-04-2008, 12:49 PM
ghe
 
Default disk names at boot

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NN_il_Confusionario wrote:

> In my opinion, udev is pretty useless on a machine where hardware does
> not change and manual loading from /etc/modules in the order you want
> permits avoiding tampering with udev rules.

Thanks, Sr. Confusionario. I agree -- and the headers in your email are
a good read...

> No warranties (even if I am VERY happy with the udev - free machines).

None expected, but you've suggested lots of fun experiments.

Now the important question: How did you find all this? Just f'ing around??

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Glenn English
ghe@slsware.com

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Old 11-04-2008, 01:52 PM
NN_il_Confusionario
 
Default disk names at boot

On Tue, Nov 04, 2008 at 06:49:54AM -0700, ghe wrote:
> How did you find all this?

upgrading from old udev-free distributions installed on old hardware, and
reading documentation.

One point not directly covered by the documentation: umount -l is useful
when you remove udev (or when on package installation udev insists on
managing /dev/ even if you have previously installed a configuration
file which says otherwise)

--
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Informatica=arsenico: minime dosi in rari casi patologici, altrimenti letale.
Informatica=bomba: intelligente solo per gli stupidi che ci credono.


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