[vox-tech] install with /usr on external HD

[Jonathan Stickel]

I'd like to share how I've recently installed Linux on a laptop with 
/usr, /opt, and /home mounted on an external Firewire drive.  This was 
necessary because of the extremely limited space on the dual boot 
internal drive of the laptop.

The distribution is Gentoo, but I'm sure the concepts will work with 
most distributions.  During the install you must have the external drive 
attached and visible.  Firewire drives show as scsi devices (e.g. 
/dev/sda).  I installed /, swap, and /boot as separate partitions on the 
internal drive (hda), and /usr, /opt, and /home as separate partitions 
on the external drive (sda).  I put them all as standard entries in 
/etc/fstab.

I made sure that all the firewire support I needed was compiled in the 
kernel, or as modules.  The key step is bringing up the firewire drive 
early in the boot sequence.  With Gentoo, you can have arbitrary kernel 
modules loaded early in the boot sequence, which I did with ieee1394, 
ohci1394, and spb2.  Then I had the script "rescan-scsi-bus.sh" 
(http://www.garloff.de/kurt/linux/rescan-scsi-bus.sh) run from within 
the /etc/init.d/checkfs and /etc/init.d/localmount scripts.  This scans 
and detects the firewire drive before fsck or mounting is attempted. 
rescan-scsi-bus.sh needs the executables seq, tail, and pr.  I moved 
these from /usr/bin to /bin since /usr/bin isn't initially available. 
Once the firewire drive is detected, the partitions can be fscked and 
mounted as normal!

I tried to create a separte /etc/init.d script to scan for the firewire 
drive, but I was unable to make it run early enough (i.e. before checkfs 
and localmount).  Anyway, hacking checkfs and localmount works just fine.

Maybe this helps someone.  I remember seeing interest about doing 
something like this in the past.

Regards,
Jonathan