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boot from backup copy of fc5 on usb external disk?



main fc5 system on sda1
[byers bootp drhmail09]$    uname -a
Linux bootp 2.6.17-1.2174_FC5 #1 Tue Aug 8 15:30:55 EDT 2006 i686 i686 i386 GNU/Linux

I am trying to boot from a backupcopy of my mainfc5
which backupcopy is in top dir of the usb disk /dev/sdc1
mounted as /media/disk-1  when in mainfc5
that usbdisk is one large reiserfs partition sdc1

1) first problem
 if i use in grub.conf in a new stanza
root (hd2,0)   corresponding to /dev/sdc1
then boot fails immediately  "hd2 does not exist"

I also note that when booting my mainfc5
there is an early message (not seen in dmesg) something like
  cant find special .../dev/sdc1
then later in the boot process it does find sdc1:
[byers bootp drhmail09]$ dmesg |grep sdc1
 sdc: sdc1
ReiserFS: sdc1: found reiserfs format "3.6" with standard journal
ReiserFS: sdc1: using ordered data mode
ReiserFS: sdc1: journal params: device sdc1, size 8192, journal first block 18, max trans len 1024, max batch 900, max commit age 30, max trans age 30
ReiserFS: sdc1: checking transaction log (sdc1)
ReiserFS: sdc1: Using r5 hash to sort names  

both pieces of evidence imply
that usb disk not available early enough in the boot process

Is there any fix for this or a workaround?



2) second problem
if i cheat and copy the /boot dir from the usb fc5copy  into /dev/sdb3
and use   root (hd1,2)  in grub.conf
then  again attempting to boot from usb  gets to ok booting the kernel

but shortly fails with "could not find /dev/root" and other "couldnotfind"

then kernel panic,locks up
 googling "could not find /dev/root"
reveals that this has been a problem in several fedora last few yrs,
 (most or all of them _not_ using external usb disk)
 fc6,fc7 maybe i saw one on fc8 as well
but no clean solution, in general not obvious (to me) why it occurred.
 some cases helped with use LABELs, some not. ( i tried this, no help)
 some cases helped with complex(to me) mkinitrd
 some cases helped with earlier kernel, but i dont see explanation of why



 In my case,
 the following stanza using an older kernel does boot!
 but has other problems.  eg networking not avail until i do a 2nd boot
 I got the older kernel
 from some oddball kubuntu  thing i was experimenting with way back

title FC5copy (2.6.15-26-386) usbfc5 /media/disk-1 (hd1,2)sdb3 rootusb
     root (hd1,2) ## sdb3
     kernel /boot/vmlinuz-2.6.15-26-386 ro root=LABEL=rootusb  rhgb quiet
     initrd /boot/initrd.img-2.6.15-26-386

this kernel 2.6.15-26-386  instead of what i use in mainfc5
            2.6.17-1.2174_FC5

Is there any current advice re "could not find /dev/root"?
has anyone seen it in f8,f9,f10?

thanks for any advice
yes i know i should get f9 or f10.  
but i would like to see if I can find clean method to
booting from usbexternal disk.

Jack

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