Re: LVM root?

[dtutty@porchlight.ca]

On Sun, Oct 08, 2006 at 10:15:22PM +0200, Jean-Luc Coulon (f5ibh) wrote:
> Le 08.10.2006 18:05:23, dtutty@porchlight.ca a ?crit?:
 
> >
> >Obviously, I don't know how LV works internally.  If the root
> >filesystem
> >get corrupted, how do I fix it from a recovery shell (e.g. the install
> >USB) if its on an LV?  If this is trivial, then is the thing to do to
> >make all of the disk a PV then have LVs for everything?
> 
> It is probably a confidence problem.
> A corrupted root file system is not better than a corrupted root over  
> LVM.

I'm confident that I don't know enough about LVM yet to rescue a mangled
system.  In the past, if something got corrupted (lightening strike,
powerfailure, disk failure, etc), I could pop in my grub disk, and
either boot my regular kernel or the one on the copy of /boot on a
diferent drive, tell it root=/dev/hda5 init=/bin/sh and start fixing it.

If that didn't work, I'd boot a rescue system (e.g. the install floppy
or CD) and manually fsck the partitions.

I suppose this is the key to my understanding and will make all clear:
Where do I tell the grub disk (USB stick?) to find the kernel and what
root= line do I give the kernel?  With / and /boot part of LVM, how does
grub find the kernel to boot?  The grub-howto and docs don't mention LVM
at all.

With regular partitions, if the partition table gets corrupted, its
simple to fix if I have what it looked like before using sfdisk -d (I
never ran into this problem after the table corruption that prompted me
to keep this information on a floppy with other essential backups).

What is the LVM equivalent of this?

The whole HOWTO package is getting woefully out of date.  LVM-HOWTO
doesn't cover recovering from errors, MULTI-DISK-HOWTO doen't cover LVM,
and the various recovery howtos focus on bare-metal recovery not fixing
a broken system.

Or, it it the case now that LVM is so reliable that any errors will be
hardware and unrecoverable anyway, requiring a bare-metal recovery.

Thanks,

Doug.