[LUNI] Setting up / on an LVM

[Martin Maney]

On Wed, Feb 09, 2005 at 03:25:02PM -0600, Trev Peterson wrote:
> That's no longer the case (at least with the grub included in Gentoo
> 2004.3).

That has never been the case IME.  At least not for Linux's native
RAID1 mirrors; striping or higher-order RAID or anything compatible
with whatever the cheap "RAID" cards that are just a more or less
proprietary software RAID do, I wouldn't expect to Just Work.

Linux's software RAID, at least since the version that supported
in-kernel recognition and configuration (which IIRC is referred to as
0.9 and/or 10, depending on what source you're looking at - in any event
it's several years old by now) places its magic header stuff at the end
of the physical partition, so for RAID1 the partition looks, to the
BIOS and all other RAID unaware code, like a regular partition, with
maybe a little extra space at the end not used by the filesystem.

(and it's easy to setup the booting to work from either drive.  Just a
quick "setup (hd1) (hd0,0)" installs the 2nd drive's MBR loader; the
mirroring will have put the stuff it's looking for at the same disk
addresses unless you partitioned the drives differently, and why would
you do that?)

> > On Wed, 2005-02-09 at 09:29 -0600, Jay Strauss wrote:
> > > Is it unwise to setup a box where my /boot is on mirror, and the rest of 
> > > my system is on a logical Volume Group sitting on a different mirror?

The only part of this that seems inappropriate to me is putting the
root filesystem into LVM; using a separate /boot seems silly but
harmless.  I've been mucking around with an old server with a pile of
SCSI drives, using two RAID mirrors: one for root (including /boot) and
the other for everything else managed by LVM.  It was a bit of a pain
getting Sarge to install to this setup - the then-current disk setup
tool didn't seem to be able to configure LVM on top of software RAID,
but I talked it into recognizing a pre-configured setup - but it works
just fine.  The one real snag I've run into is that it hangs on reboot
or shutdown with the distro kernels that have the RAID code in modules. 
As long as I can hit the physical switch it doesn't matter, but better
to get rid of the stock kernel for a locally built one more suitably
configured.  Gotta get around to that again...

> > > I've been googling, seems like there are mixed messages out there.  My 
> > > main concern being will I be able to boot from a rescue disk if my 
> > > system sits on a LVG.

Depends on the rescue disk.  If your rescue disk is a modern CD-based
thing, I shouldn't think there would be a problem.  Another possibility
is to setup a small (1G is more than adequate with Debian) maintenance
partition with an independent install.  Makes a great place to stand
when you need to rearrange the world, or just looks at it from a
different point of view.  :-)

-- 
The phenomenon of financial excess associated with
promising novel technologies is a recurring feature
of the last two centuries.  -- Andrew Odlyzko