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Re: device syntax again

From: Yoshinori K. Okuji
Subject: Re: device syntax again
Date: Wed, 19 Jan 2005 11:06:58 +0100
User-agent: KMail/1.7.1

On Wednesday 19 January 2005 02:59, Hollis Blanchard wrote:
> Here is what I see happening:
>       > boot /address@hidden,0/<tab><tab><tab>
>       >
>       > boot 
> /address@hidden,0/address@hidden,1/address@hidden/address@hidden,0
>       No such device
>       > alias thatdisk 
> /address@hidden,0/address@hidden,1/address@hidden/address@hidden,0
>       > boot thatdisk
> I don't think GRUB can automatically create aliases in this case.

I don't understand this. Could you elaborate on this in details?

> I agreed at the time, but the more I thought about it I changed my
> mind.


> It is true that many home users do not understand technical things.
> It is also true that advanced users (e.g. users with complex
> hardware) must be allowed to do advanced things without being forced
> into a too-simple model...

It is not too simple. You are allowed to make an arbitrary alias on 
GRUB, so you just need to do one more step to access a drive.

alias my_drive /some/path
root (my_drive)

This should be acceptable for experts. Do I miss anything?

> Users must be expected to learn how to boot their new
> architectures... In the case of a small Open Firmware system, this
> need not be any more complicated than an x86 PC. In the case of a
> large Open Firmware system, though, users will need to become at
> least slightly familiar with their firmware. I speak from experience
> here. :)

I don't think so, if the software is good.

For instance, when I installed Debian GNU/Linux into my iBook, all I had 
to learn was how to boot a CD-ROM from Open Firmware (pressing 'c' or 
something like that). The other dirty jobs were done by yaboot and 
ybin. So I didn't need to learn anything about the device syntax.

The reason why I know Open Firmware somehow is simply because I studied 
it intentionally when Gordon and I were thinking of porting GRUB to 
other architectures (and I played Open Firmware with SparcStation and 
PowerBook). For most people, there is no reason why they must learn 
Open Firmware.

> I agree, phone support would be difficult, but also very unlikely. :)

It happens frequently in the support section of each vendor working with 
GNU/Linux. For example, I know Red Hat does this.

> Even on small systems, the difficulty in naming is easy to see. I
> have one SCSI disk and one ATA disk. Which is "the first"? On a PC I
> guess you would say "it depends on the BIOS and SCSI BIOS, but the
> ATA disk is probably first". With Open Firmware, the question is
> unambiguously answered.

I have never said that you should not distinguish SCSI from ATA.

> The systems I use may have dozens of PCI buses. Each bus may contain
> many PCI SCSI adapters, and each adapter may have many disks
> attached. How would you number these devices? (The bus connections do
> not match the physical positions, so you cannot say "the top left
> disk is #0, the next to the right, is #1, etc".)

In this kind of configuration, you should specify a drive logically, 
otherwise it is unmaintainable.

I have a more confusing example in our company. The machine uses an 
internal ATA disk and many Firewire disks. Unlike SCSI, Firewire disks 
do not have IDs, so there is no way to expect how to count (name) the 
disks. And, we sometimes want to connect a new disk and disconnect a 
disk, which must not affect the booting process of the machine.

Currently I'm using disk labels to address this issue. Although GRUB 
does not support disk labels (at the moment), this is not a problem 
only because I use the internal ATA disk to boot the machine.

Suppose that you have a machine only with Firewire disks and you want to 
boot it from one of the disks... Probably any kind of physical way does 
not help you. It is necessary to let GRUB find a desired disk in a 
logical way. You could use a disk label, an UUID or a filename for 

> Most of us have only had to deal with small computers, and I agree
> that things should be optimized to make life as easy as possible for
> these users. However, please also keep large systems in mind. Try to
> imagine yourself in front of a small rackmount system with only 12
> hotplug disks wondering which one is /dev/sda under Linux. Then
> imagine you need to hotplug the correct disk into another system, and
> after telling firmware to boot from the new disk, GRUB and Linux
> "just work". It is hard to imagine, but I hope we can agree that such
> users have different needs from our aunts sitting at their PCs at
> home. Thanks!

Don't worry. I have experience with large systems, and I take it into 
account. I think using disk labels is a good answer for your question.


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