Sharing an external USB hard rive - can you boot Mac and Windows?

I'm using an external USB2 hard drive (Western Digital 250 Gb) to back up my MacBook and a couple of Dell laptops. It's formatted FAT32, so both OSes work fine with it, and I think the Dells can boot from it. It's fine for backing up files, although SuperDuper turns up its nose because it's not HFS+.
I've learned from these forums that an Intel Mac can boot from a USB drive but only if it's formatted properly, not FAT32. I think you need a GUID partition map and HFS+ formatting.
So, is there ANY way I could use this drive as a bootable backup for BOTH a MacBook and a Dell (Windows XP) laptop? I've looked around a lot, and I think it cannot be done. Anyone know otherwise?

Yes, no question about that.
What I was wondering is if there might be any partitioning and formatting strategy whereby there could be a "Mac" partition and a "Windows" partition, so that either machine could boot from the same external (USB) drive.
Obviously, Apple has achieved dual-boot with BootCamp for internal drives but I can't find any comparable solution for external drives.

Similar Messages

I w system from OSX 10.5.8 to at least 10.6. Also my hard drive is partitioned for Mac and Windows (which I would like to remove). How should I upgrade?

I want to buy an Iphone 5 but need to upgrade my operating system from OSX 10.5.8 to at least 10.6.0. Also my hard drive is partitioned with Mac and Windows. How can I upgrade?

1. Click here and buy a Mac OS X 10.6 DVD.
2. Use the Boot Camp Assistant in the /Applications/Utilities/ folder to return the drive to a single partition setup.
(83003)

HT1452 I want to reset the permissions on a western digital external hard drive to work between mac and windows... How can I do this easily?

I have a MacBook Pro and have recently bought a Western Digital external hard drive. I used it on my windows laptop first and unfortunately now on the Mac it is read only. How can I set it so that I can use it successfully between the both the Mac and windows laptop?
Thanks

MacQuack wrote:
You will need to pull all the information off first. The formatting will erase it all.
Use Disk Utility (in Applications >> Utilities or use Spotlight to find it). On the left select your WD drive and then select the Erase tab. Where it says Format, select exFat in the drop-down menu. Next, click Erase and done. It will take approx. 5-15mins to re-format.
Cons: You will be unable to store files 4GB or larger in this format (usually only dmg/iso files or large Outlook files). Also, you will be unable to use Time Machine or other auto-backup programs.
That is not entirely correct, there is no 4G limit using exFat, FAT32 is the one with the limit.

External hard drive use with both Mac and Windows

I know that you can't use an iPod (through iTunes) with both Mac and Windows, but can you still use it as an external hard drive with both operating systems?

Yes, if the iPod is in Windows format. Mac OS X can read and write Windows formatted iPods, but Windows can't access Mac formatted disks unless special software is installed.
(9844)

External USB Hard Drive Can't Be Safely Removed After Boot Camp 3.1 Install

I just wanted to report that I've done multiple installs of Windows 7 Ultimate 64-bit on my MacBook 4,1 and although I've had no problem using the cmd workaround ( http://www.zath.co.uk/how-to-install-windows-7-on-apple-mac-boot-camp/ ) to install the 64-bit Boot Camp drivers that come with the Mac OS X 10.6 Snow Leopard retail DVD, I have found that by installing the Boot Camp 3.1 drivers on the same system, under no circumstance can I click the the "Safely Remove Hardware" icon in the system tray and not receive a message saying that ... "The device 'Generic Volume' cannot be safely ejected..." and that some program or service must be using it. However, a restart doesn't solve the problem any more than logging out does.
I read somewhere that part of the fix that Boot Camp 3.1 was intended to provide was to allow safe ejecting of the Macintosh HFS+ partition. Well, my external hard drive has three partitions: one NTFS, another NTFS, and a third HFS+ for Time Machine backups. I suspect, since I haven't seen anyone else reporting this issue, that it may simply be that the Boot Camp 3.1 drivers don't take into account the possibility of an HFS+ partition on external USB devices. Anyway, a System Restore to before Boot Camp 3.1 drivers were installed completely remedies the issue.
At this point, I'm not having any trackpad issues or anything else of note with respect to the original Boot Camp 3.0 drivers that came with the Snow Leopard retail disc, so I'm fine keeping those drivers installed and allowing Windows Update to update the Intel and Marvell drivers as it recommends. I just find it slightly amusing that the Boot Camp 3.0 drivers, which supposedly did not support Windows 7 (let alone the 64-bit version) work better than the 3.1 drivers which do supposedly support Windows 7. And the funny thing (or is it?) is that you have to install the original Boot Camp drivers with the cmd workaround before you're even able to update to the Boot Camp 3.1 drivers. Hilarious stuff there.
Proprietary gamesmanship is a big reason some of us prefer the Linux "share the ownership +for free+" model of computing. Just saying...
Anyone have any proper solutions (as in, other than "don't install the updates then!")?
bkadoctaj

I have a pair of external usb drives, one formatted for NTFS and the other for HFS+ connected through an external 7 port hub. I am running Windows 7 (64 bit) with bootcamp 3.1 on a late 2009 Mac BookPro. I share the same "safely remove hardware" issues you described. I always assumed it was because my external drives were connected through my external USB hub because of a similar issue I had running Vista (64 bit), but now I can confirm directly connecting the external USB HFS+ drive also yields the same "safely remove hardware" problem. Unfortunately for me, if I regress to the Bootcamp 3.0 drivers, my audio drivers, at times, fails to load. I would need to regress to Windows Vista (64 bit), the last environment where my iSight camera, internal speakers and all other hardware performed correctly. I would gladly, at this point, live with the "safely remove hardware" issue in exchange for a working iSight camera, the one and only hardware device lost to me in the move to Windows 7.

External USB hard disk fails to boot

I installed Arch Linux on an external USB Lacie 1 TB Hard Disk. I followed instructions on WiKi: "install from exisiting linux", method 2, since I already have Linux installed
on the internal HDD of my laptop (dual boot with Windows, also with Grub as bootloader).
Problem: The external HDD stalls during boot right after the "Welcome to Grub!" - message. I can only hard-reset my laptop from there.
The external HDD has msdos Partition Table. It is recognized by BIOS just fine, since I can choose to boot from it. It has following (very simple) partition setup:
[root@arch-laptop chris]# fdisk -l /dev/sdb
Disk /dev/sdb: 931.5 GiB, 1000204886016 bytes, 1953525168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x000c9610
Device Boot Start End Blocks Id System
/dev/sdb1 * 2048 40962047 20480000 83 Linux
So there's just the root partition, no boot or home partition defined. Grub installed to the external HDD with no errors.
Here's the grub.cfg auto-generated, without anything adapted. The UUID of the external HDD /dev/sdb1 is correct.
[root@arch-laptop grub]# cat grub.cfg
# DO NOT EDIT THIS FILE
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
### BEGIN /etc/grub.d/00_header ###
insmod part_gpt
insmod part_msdos
if [ -s $prefix/grubenv ]; then
load_env
fi
if [ "${next_entry}" ] ; then
set default="${next_entry}"
set next_entry=
save_env next_entry
set boot_once=true
else
set default="0"
fi
if [ x"${feature_menuentry_id}" = xy ]; then
menuentry_id_option="--id"
else
menuentry_id_option=""
fi
export menuentry_id_option
if [ "${prev_saved_entry}" ]; then
set saved_entry="${prev_saved_entry}"
save_env saved_entry
set prev_saved_entry=
save_env prev_saved_entry
set boot_once=true
fi
function savedefault {
if [ -z "${boot_once}" ]; then
saved_entry="${chosen}"
save_env saved_entry
fi
function load_video {
if [ x$feature_all_video_module = xy ]; then
insmod all_video
else
insmod efi_gop
insmod efi_uga
insmod ieee1275_fb
insmod vbe
insmod vga
insmod video_bochs
insmod video_cirrus
fi
if [ x$feature_default_font_path = xy ] ; then
font=unicode
else
insmod part_msdos
insmod ext2
set root='hd1,msdos1'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos1 --hint-efi=hd1,msdos1 --hint-baremetal=ahci1,msdos1 5fe1d28c-2640-4b5c-b98b-75d147479348
else
search --no-floppy --fs-uuid --set=root 5fe1d28c-2640-4b5c-b98b-75d147479348
fi
font="/usr/share/grub/unicode.pf2"
fi
if loadfont $font ; then
set gfxmode=auto
load_video
insmod gfxterm
set locale_dir=$prefix/locale
set lang=en_US
insmod gettext
fi
terminal_input console
terminal_output gfxterm
if [ x$feature_timeout_style = xy ] ; then
set timeout_style=menu
set timeout=5
# Fallback normal timeout code in case the timeout_style feature is
# unavailable.
else
set timeout=5
fi
### END /etc/grub.d/00_header ###
### BEGIN /etc/grub.d/10_archlinux ###
menuentry "Arch Linux pkg-linux kernel" --class arch-linux --class arch --class gnu-linux --class gnu --class os {
if [ x$feature_all_video_module = xy ]; then
insmod all_video
fi
set gfxpayload=keep
insmod ext2
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos1 --hint-efi=hd1,msdos1 --hint-baremetal=ahci1,msdos1 5fe1d28c-2640-4b5c-b98b-75d147479348
else
search --no-floppy --fs-uuid --set=root 5fe1d28c-2640-4b5c-b98b-75d147479348
fi
echo 'Loading Arch Linux pkg-linux kernel ...'
linux /boot/vmlinuz-linux root=UUID=5fe1d28c-2640-4b5c-b98b-75d147479348 rw quiet
echo 'Loading Arch Linux pkg-linux kernel initramfs ...'
initrd /boot/initramfs-linux.img
menuentry "Arch Linux pkg-linux kernel (fallback initramfs)" --class arch-linux --class arch --class gnu-linux --class gnu --class os {
if [ x$feature_all_video_module = xy ]; then
insmod all_video
fi
set gfxpayload=keep
insmod ext2
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos1 --hint-efi=hd1,msdos1 --hint-baremetal=ahci1,msdos1 5fe1d28c-2640-4b5c-b98b-75d147479348
else
search --no-floppy --fs-uuid --set=root 5fe1d28c-2640-4b5c-b98b-75d147479348
fi
echo 'Loading Arch Linux pkg-linux kernel ...'
linux /boot/vmlinuz-linux root=UUID=5fe1d28c-2640-4b5c-b98b-75d147479348 rw quiet
echo 'Loading Arch Linux pkg-linux kernel fallback initramfs ...'
initrd /boot/initramfs-linux-fallback.img
### END /etc/grub.d/10_archlinux ###
### BEGIN /etc/grub.d/10_linux ###
menuentry 'Arch Linux' --class arch --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-5fe1d28c-2640-4b5c-b98b-75d147479348' {
load_video
set gfxpayload=keep
insmod gzio
insmod part_msdos
insmod ext2
set root='hd1,msdos1'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos1 --hint-efi=hd1,msdos1 --hint-baremetal=ahci1,msdos1 5fe1d28c-2640-4b5c-b98b-75d147479348
else
search --no-floppy --fs-uuid --set=root 5fe1d28c-2640-4b5c-b98b-75d147479348
fi
echo 'Loading Linux linux ...'
linux /boot/vmlinuz-linux root=UUID=5fe1d28c-2640-4b5c-b98b-75d147479348 rw quiet
echo 'Loading initial ramdisk ...'
initrd /boot/initramfs-linux.img
submenu 'Advanced options for Arch Linux' $menuentry_id_option 'gnulinux-advanced-5fe1d28c-2640-4b5c-b98b-75d147479348' {
menuentry 'Arch Linux, with Linux linux' --class arch --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-linux-advanced-5fe1d28c-2640-4b5c-b98b-75d147479348' {
load_video
set gfxpayload=keep
insmod gzio
insmod part_msdos
insmod ext2
set root='hd1,msdos1'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos1 --hint-efi=hd1,msdos1 --hint-baremetal=ahci1,msdos1 5fe1d28c-2640-4b5c-b98b-75d147479348
else
search --no-floppy --fs-uuid --set=root 5fe1d28c-2640-4b5c-b98b-75d147479348
fi
echo 'Loading Linux linux ...'
linux /boot/vmlinuz-linux root=UUID=5fe1d28c-2640-4b5c-b98b-75d147479348 rw quiet
echo 'Loading initial ramdisk ...'
initrd /boot/initramfs-linux.img
### END /etc/grub.d/10_linux ###
### BEGIN /etc/grub.d/20_linux_xen ###
### END /etc/grub.d/20_linux_xen ###
### BEGIN /etc/grub.d/30_os-prober ###
### END /etc/grub.d/30_os-prober ###
### BEGIN /etc/grub.d/40_custom ###
# This file provides an easy way to add custom menu entries. Simply type the
# menu entries you want to add after this comment. Be careful not to change
# the 'exec tail' line above.
### END /etc/grub.d/40_custom ###
### BEGIN /etc/grub.d/41_custom ###
if [ -f ${config_directory}/custom.cfg ]; then
source ${config_directory}/custom.cfg
elif [ -z "${config_directory}" -a -f $prefix/custom.cfg ]; then
source $prefix/custom.cfg;
fi
### END /etc/grub.d/41_custom ###
### BEGIN /etc/grub.d/60_memtest86+ ###
### END /etc/grub.d/60_memtest86+ ###
the internal HDD (/dev/sda) also has GRUB installed, without any problems, with a graphical console menu.
GRUB version is 2.02
laptop: dv6-6b41ed
Legacy BIOS (no EFI / UEFI).
Any ideas on how to solve / troubleshoot this?
Last edited by christopher72 (2014-04-21 15:05:21)

Any hooks in particular? I don't know which hook to add other then the 'blocks' hook, which is there already:
HOOKS="base udev autodetect modconf block filesystems keyboard fsck"
Also, I don't think that could be the problem since loading the initramfs image takes place after choosing something from the Grub Menu. That menu never appears, I just get "welcome to grub!" with a blinking cursor underneath.
I did add "insmod usbms" in grub.cfg, but that didn't change anything.
What strikes me as odd is that in grub.cfg, the disk is referred to as "hd1", where I think it could just as well be "hd0" if that's the first hard disk the BIOS boots from. But I'm not sure if that really matters since the search is done with the UUID.
Another thing I tested earlier: I dd 'd the Arch Live image to the external usb HDD, and then it boots fine...

Can you partition an external hard drive to run both mac and windows files

I have an external hard drive fomated for windows NTFS. I am unable to Write mac files to this drive. I need to be able to share the files
between both platforms. Any suggestions? Thanks

Format it as MS-DOS from a Mac or exFAT from a PC, or install Mac OS X software which allows it to write to NTFS drives, or hook it up to a PC and make it available as a network share.
(78564)

Initiating external usb hard drive that has been formatted for Windows

I have a 400GB USB external hard drive and it was working fine until I tried to erase it in disk utility and it wouldn't work and kept causing disk utility to freeze up and it was very difficult to force quit even.
I took it to a PC shop and they reformatted it for windows and it worked on their windows so I thought I would try and reformat it again in disk utility to run on mac but it just did the same things and froze again.
If anyone can understand what I am babbling about could you please give me some advice before I give up
Thanks
Kevin

No it has to be formatted for OS X. Mac Extended (Journaled).

I have an external hard drive that is both Mac and Windows compatible and can no longer delete any files. I recently reformatted my Mac, does this have anything to do with it?

I've clicked on the 'get info' tab, but it says read only for all files.

You can't write to it because it's formatted as NTFS which OS X will read but not write to. If you want to continue using the drive with both a PC and OS X you will need to download and install NTFS-3G so you can then write to it from your Mac. You can get NTFS-3G at:
http://www.macupdate.com/app/mac/24481/ntfs-3g
If you want to use the drive exclusively with your Mac then move the data off it and reformat it in Disk Utility (Applications - Utilities - Disk Utilities) as Mac OS Extended (Journaled.)

I recently purchase macbook air with OS 10.10.2. I want to use my Seagate external backup plus hard drive for time machine back up. How to partition my 1TB Seagate back up plus hard drive for use with mac and windows pc?

Hi All,
I recently purchased 13" Macbook Air with OS 10.10.2. I want to use my 1TB Seagate backup plus external hard drive as time machine and my windows 7 pc. Please suggest a method. Thanks in advance for your reply.

I strongly recommend having an external drive dedicated solely for TimeMachine. You could partition the drive but if something goes wrong you risk losing the data on both partitions. Should you decide to go ahead with splitting the drive for two different uses you’ll need to partition the drive either using the Mac’s built in Disk Utility program or Windows utility. I believe the built in Windows disk utility program will destroy the current partition and erase the data that’s on it - I use a third party Windows disk utility program for partitioning and it allows for non-destructive partitioning but warns to back up data first just in case. Apple’s Disk Utility can do non-destructive partitions but I don’t recall every trying to do a non-destructive partition on a disk originally formatted for Windows using it. Again - back up that data just in case.
Finally, your TimeMachine drive should be at least 1.5 times (I prefer 2 times) the size of the data you expect to be backing up a year or two from now. In other words, if you currently are using 50GB of your computer’s drive but expect to begin purchasing Mac software to replace software on your Windows computer and if you expect to be putting photos, music, and other data on it you might expect that two years from now you’ll have 100GB of stuff on the drive. So a 200GB partition is the smallest size you’d want. TM’s backup scheme keeps multiple copies of data as it changes so the extra room is important for this scheme.

FORMAT HARD DRIVE FOR USE ON MAC AND WINDOWS

I'm going to start working on scanning a lot of old family photos and getting them put on an external hard drive for my parents. I'd also like to eventually put old VHS family home movies on the hard drive as well. However, I'm not sure what to do about the hard drive. I know if I format it to be compatible with my Mac it probably won't be compatible with their PC. I read about the FAT32 option but I saw something about a file not working if it's over 4 GB in size. I'm thinking maybe some of those home movies will be larger than 4GB. I also saw an exFAT option. If I go with that will I be able to scan the photos on my Mac, get the home videos converted and put it all on the hard drive will all of it be visible and usable on their Windows PC?
Thanks for your help!

matahari_1946,
if you’re not yet backing up your Mac’s internal hard disk, I’d recommend first that you purchase an external hard drive for yourself for exclusive use as a Time Machine backup destination; that way, in case of a disk problem, you won’t permanently lose all of your scanned photos and imported movies.
A 4 GB file limit does apply to FAT32 filesystems. If their version of Windows allows, the external disk which will hold those photos and videos should be formatted as NTFS from their PC, so that they can watch video files over 4 GB. (It’s unlikely that an individual photo file would be over 4 GB.) However, OS X doesn’t come out of the box with NTFS support. The exFAT filesystem is able to hold files over 4 GB, and it is supported by Mac OS X 10.6.5 and newer, but it’s optimized for flash drives; it’s more “fragile” on hard disks than other filesystems are. As a workaround, you could format a flash drive to have exFAT, copy videos over 4 GB onto the flash drive, and then use your parents’ PC to copy the videos from the flash drive to their NTFS external disk. Other alternatives would be to look for third-party software for OS X which supports reading from and writing to NTFS disks, or third-party software for Windows which supports reading from and writing to journaled HFS+ (the default OS X filesystem) disks.

Can I use Mac and Windows interchangeable with Creative Cloud?

I'm pondering getting a creative cloud membership. As I work on windows and mac, it would be great if I could work off a mac at home one day then work off a windows pc at work the next. Does creative cloud allow me to do this?

Hi Mx,
With creative cloud , you get the option to install the product on a windows and Macintosh both . Also , one single license can be installed on upto two machines as well .
Kartikay S

Can sync to mac and windows with the same device

I just bought my partner an iphone, and he wants to know if once activated through itunes, will the phone sync to any computer regardless of the operating system as long as itunes is installed. We have Macs at home but he has windows in the office.

iphonecuty...I connect & sync my iPhone with an iMac at home and a Windows PC at work. However, the work PC only syncs my calendar and contacts; all of the iTunes content is synched only from the iMac. Works fine this way.
HTH
QS

How can I do backups on internal disc while sharing an external USB drive?

Hi,
On my Airport Utility there are two lines: "Time Capsule Disc", and below (indented) "Data".
(When I plug an external USB drive I can see it in this window as well)
Clicking (selecting) the first line, on the right hand side I can see the disc details (name, capacity and SMART Status (Verified)), and two buttons: Compress and Erase (I don't know if these are the words used on the english version mine is spanish).
Clicking on the second line (Data) I can see the Name "Data", capacity, used and available sizes and number of users connected.
First question:
Why Time Machine can't see the "Data" volume if I untick the "Share files" checkbox?
Second question:
Moreover, I've got a USB External Drive attached to my Time Capsule, so I have to have the "Share Files" checkbox ON, this makes my USB disc (fat32) available to my Windows computers but ALSO the "Data" volume can be seen from Windows. If there is any attempt to assign a Windows drive letter to the "Data" volume, next time Time machine wants to do a backup I'm getting a "disc wrong or missing, check credentials (or something similar)".
In summary, what I'm trying to do is Time Machine backups to the internal Time Capsule disc (making that disc unavailable/invisible to any other computer in my network) while sharing a USB external drive attached to Time Capsule.
Advice, please!

Yes you can go to > Music > iTunes folder and copy the whole iTunes folder and drag the folder to your external and then on the new Mac click and highlight the iTunes folder and then in iTunes click on the button at the top (add folder to library) and you should see all your songs transfer from the external to the Mac and all songs start filling up in your iTunes library on the Mac.
This is the easiest method all songs and other media such as songs, movies, apps will be transferred over however you may not be able to keep ratings & last played counts using this method.
To keep all metadata including ratings & play count use the Apple method exclusively for this if you have to have your metadata, play counts and ratings saved.
I used scenario one above because it one of the simplest methods and I was just satisfied enough just to transfer all media over.

Arch: Install to & run from External USB Hard Disk Drive (HDD)

I wanted to play with ArchLinux 2009.02, but replacing the existing Debian-Lenny on the laptop's HDD wasn't an option. So I experimented with installing Arch on an external USB Hard Disk Drive.
I have tried to make this "newbie-friendly", so I hope the more experienced will forgive the detail.
Materials:
Three year old Dell Inspiron 6000
CPU = 2.0 GHz Pentium
RAM = 2.0 GB
Internal HDD = 80 GB
Internal CD/DVD R/RW
External USB HDD = Freecom FHD-2 Pro 80 GB
Archlinux 2009.02 install CD
Steps to install:
1. I put the Archlinux install CD in the drive and connected the external 80 GB HDD in the USB port.
2. When the Dell laptop was booted, I pressed F2 to enter the BIOS setup. I edited the boot sequence to the following:
Internal CD/DVD
External USB device
Internal HDD
On the Dell, you can also press F12 to select the preferred boot device for that boot.
3. I started the laptop and the Archlinux installation menu came up and I proceeded with installation following the "Official Arch Linux Install Guide" and the "Beginners Guide".
4. Used km to change to UK keyboard layout and then began the installer script (/arch/setup). I was installing from the core CD so I skipped the network steps.
5. HDD preparation.
This was fairly straightforward with two cautions:
(a) Make very sure that the external HDD (sdb) is selected for the operations.
(b) Remember to set the Bootable Flag for the first (/) partition on the HDD.
I chose 20 GB for /, 2 GB for swap and the remainder for /home.
6. The package selection and installation was fairly straightforward.
7. Configuration of System
This was section was straightforward with one warning:
USB had to be added to the HOOKS in the /etc/mkinitcpio.conf file!
I found this to be essential for my external USB HDD to function as a bootable device. Otherwise I got the same sorts of errors relating to unrecognisable file system types that other people have reported in the forum.
The relevant line from the end of the edited /etc/mkinitcpio.conf file is below:
HOOKS="base udev autodetect pata scsi sata usb filesystems"
8. Installation of GRUB was the other point where caution and/or correction was necessary.
When it asked where GRUB should be installed, I had to select sdb (my external USB HDD) and not any of the particular partitions on sdb. If the root partition sdb1 was selected then the laptop won't boot from the external USB HDD.
The GRUB /boot/grub/menu.lst as written by the installation routine specifies hd(1,0) which doesn't work when you try to reboot from the external USB HDD. When you boot Arch from the external USB HDD, as far as Arch is concerned - at that point in time - the external USB HDD is the first drive in the system. To fix this:
(a) When the Arch boot menu comes up, press e to edit the grub entries.
(b) Change the first line to hd(0,0)
(c) To the end of the kernel line add rootdelay=8
(d) Press b to boot the system with these temporary corrections.
(e) Once your Arch system has booted, edit the /boot/grub/menu.lst to make the above changes permanent.
The relevant portion of my /boot/grub/menu.lst looks like the following:
# (0) Arch Linux
title Arch Linux
root (hd0,0)
kernel /boot/vmlinuz26 root=/dev/disk/by-uuid/... ro rootdelay=8
initrd /boot/kernel26.img
# (1) Arch Linux
title Arch Linux Fallback
root (hd0,0)
kernel /boot/vmlinuz26 root=/dev/disk/by-uuid/... ro rootdelay=8
initrd /boot/kernel26-fallback.img
9. The laptop happily and consistently boots Arch Linux from the external USB HDD when it's plugged in before startup/booting.
Running Arch from the external USB HDD seems as quick as running Debian from the internal HDD.
So if there is a performance penalty associated with using an external USB HDD, my wife and I haven't noticed.
In summary, the three essential points to address during installation to an external USB HDD are:
Remember to set the bootable flag for the first partition.
Add USB to the HOOKS for /etc/mkinitcpio.conf file.
Correct the /etc/grub/menu.lst file.
I hope this is helpful.
Ted

Hi Rookie,
As you say, it is worth remembering the rootfstype= option for the kernel line just in case someone still has problems with GRUB after making all the other changes.
I was working with the most recent Arch 2009.2 release.
I only got messages about unrecognisable file system type when I tried booting with the "stock" or "as-installed" GRUB (before I edited /boot/grub/menu.lst). After editing /boot/grub/menu.lst to identify the drive correctly and add rootdelay, GRUB was able to do the rest and everything worked OK without any error messages.
Best wishes,
Ted

Sharing an external USB hard rive - can you boot Mac and Windows?

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