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Re: [linux-lvm] Recovering from a disaster...

Steven Lembark wrote:

Among the things they don't have is a sane boot command prompt
that allows cleaning up the system by bypassing LVM on startup
(e.g., "boot -lm /dev/blah" on HP PARISC systems). And, yes,
this is true of Wintel-look-alike systems also, AMD has not
done any better job of leaving you with a command line at boot
to handle nasty situations.

i won't say about sgi or sun, but HP PARISC system do not provide this in firmware.

i have already posted on this list about hp systems, i'll do again (from memory so forgive any imprecisions)

hp 9000 firmware is able of identifying most hardware and of booting from disk, cd, tape or lan (dhcp + proprietary load method)

on the boot media ther is a 2Mb area called LIF area that contains an archive with some utilities (you can peek at containts using 'lifls /dev/rdsk/cXtYdZ)
hp firmware loads and runs something called ISL contained in this archive.
- end of firmware work (mostly) -

ISL is a secondary loader it can load other utilities contained in the lif.
HPUX is one of these utilities: it is able to read data from an hfs formatted filesystem and sets up the kernel using this data.
it can pass parameters to the kernel.
the magic
hpux -lm (device path)/path/to/kernel
works by reading a file contained in the same place as the kernel called rootconf, rootconf contains in binary form the offset on disk and lenght of the root filesystem.

That's all, it can be implemented with grub and linux lvm NOW if we want to accept the limit of having a fixed size contiguous root filesystem.

we can do better than that even with the crippling pc bios and we should be able to disregarding the firmware we are running from (assuming it is at least able to boot from one of (disk/tape/cd/floppy/lan)

I am strongly annoyed at ppl that continuously state 'dont put root on lvm because it is unsafe'.

the only difference between code parsing a partition table and code parsing lvm metadata is complexity, if you screw the partition table
(or if you rm /stand/rootconf on hp-ux AND screw LVM boot area) you are in the same situation.

linux already has the means of making it extremely safe and much more extensible than what other systems have. and if it is designed to work on the most crippled firmware we have (pc bios) it will certainly work with better firmware.

just create an lvm on disk format that reserves the first megabytes for a secondary loader (we can even use a linux kernel and it's initramfs as a secondary loader with 2.6).

tell the secondary loader where the root filesystem is placed (in case you screw LVM) it should not be a very complex map and it can be replicated in more than one place if necessary.

oh, we probably have to dump pc partition table format for this (too sorry :)


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