[linux-lvm] Newbie question

[Luca Berra]

sorry if i am getting way offtopic here but reply is a must

On Tue, Jul 17, 2001 at 10:31:59AM +0200, josv at osp.nl wrote:
> Hi all,
> 
> Just for the record, HP-UX's vg layout is not in /stand. Information about
> essential logical volumes (boot (/stand), root (/), primary swap and dump) 
> is stored in a LIF file (LABEL) in the boot area's of the disk (use the lifls 
> command to display the structure of the boot area). The lvlnboot command is used
i was referring to:
(from the lvlnboot manpage)
 FILES
      /stand/rootconf          Contains the location of the root volume.
                               Used during maintenance-mode boots (see
                               hpux(1M)) to locate the root volume for
                               volume groups with separate boot and root
                               volumes.

ok, i was not exactly correct but if you follow me you will maybe
pardon me.
Steven stated that hpux -lm worked because HP9000 were able to
understand LVM in firmware.
i stated that hpux -lm works because lvm info is stored in a file in
stand.

The real truth:
/stand/rootconf does not contain LVM info
it just contains info about the location on disk of the root lv
meening starting offset and lenght (it is used only on split
boot/root configurations when booting in LVM mainteinance mode)

on my workstation
# od -x /stand/rootconf
0000000 dead beef 000d 5b60 0004 0000
       | magic   | offset  | size

/stand/rootconf is created/updated using lvlnboot -c


lvlnboot updates both the LABEL file and the BRDA on the PV
the kernel during normal boot reads the BRDA, not the LABEL file
the LABEL file is used by the hpux utility, it is also used
by offline diagnostics.

> to query and change the LABEL file. The mapping between VG and PV's is stored
> in the /etc/lvmtab file. This file is used by the vgchange command to activate
> volume groups. At boot time, /etc/lvmrc is run from the inittab, and it
> executes a 'vgchange -a y' for all volume groups.
this is not strictly correct (lvmrc is a script anc can/must be customized
not to activate all VGs in a clustered environment)

> The "-lm" boot option in HP-UX disables the lv driver (major 64), so only the
> /stand, /, pri swap and dump "volumes" are available. Not as logical volumes,
> but directly from the disk because these volumes must be contiguous. This
this is just plain wrong
only root is available to the system in lvm maint mode (via /stand/rootconf)
/stand and pri swap are not, let alone dump.
/stand must be contiguous at the beginning of the boot disk so the
hpux utility can read a kernel off it
/ must also be contiguous on the boot disk so the kernel can map it
swap and dump can be on any disk (the latter only if IODC is able to
map it) and must be both contiguous. (yes primary swap does not need
to be on lvol2 and on the first disk, altough this is the default)

> option is necessary in HP-UX since it basically only supports LVM disk setups
> (whole disk layout is also supported, but almost never used...). If Linux
AFAIRC whole disk works only on disks < 1GB or so

> would ever get to the point that LVM (or its successor) is *the* choice for
> partitioning all disks (even the boot disk), we would need such an option as
> well because otherwise there would be no path to recovery in case of LVM
> data corruption.

honestly i believe having a resizable root volume is better than being able to
mount root without using lvm. since i can stick enough tools to recover lvm in
an initrd or on a emergency cd-rom.

....
> ++Jos
> "Who could not resist commenting on this, sorry..."

me neither, sorry again....

L.
-- 
Luca Berra -- bluca at comedia.it
        Communication Media & Services S.r.l.
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