How to create bootable USB external hard drive?

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Subject: How to create bootable USB external hard drive?
System: Acer Aspire M3400 desktop w/ Windows 7

My Acer desktop PC has an internal 640GB hard drive;
and I have a 2TB external USB hard drive. I would like
to copy my internal drive to the external one, so that,
if the internal one fails, I will be able to boot off
the external one and continue working while I seek a
replacement for the internal one. How to do this?


Re: How to create bootable USB external hard drive?

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Not possible with Windows. Maybe with Linux.

  Wie alles begrijpt, die alles vergeeft...

Re: How to create bootable USB external hard drive?

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Natively you could boot off an eSATA drive to run Win7, but then you would
have to also have a second copy of Win7 for it to be activated and be
constantly backing up to it to maintain the same information that you have
on your regular drive.

Alternatively you could be backing up regularly making incremental images
and if the drive either crashes or won't start have a fresh drive handy to
restore the image to it. Using Acronis TrueImage makes this a very easy
solution to what you are suggesting.

Jan Alter

Re: How to create bootable USB external hard drive?

C.M. Burns wrote:
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I'm no expert, but I did spend an hour experimenting, cause
your question was interesting.

My test machine is an old Dell 4550.
I pulled the hard drive and stuck it into an external
usb enclosure and tried to boot it.
The drive was not visible to the bios, so no dice.
I ran the winxp install CD.  Same problem.

I replaced the hdd with a usb stick containing linux.
It was recognized by the BIOS and
Booted just fine.
Inserting a non-bootable USB stick still resulted in
a USB device visible to the BIOS.  Of course it wouldn't
boot, but it was VISIBLE.  Problem appears to be with the usb
enclosure, not the computer.

Different external hdd chips have different functionality.
I don't know how to determine except to just try it.

So, your first problem is to determine if your usb drive
is visible to the bios.  Boot into the bios boot menu and see if
booting from the usb drive is there. If not, your
external drive ain't gonna do it.

I've never tried to install windows on an external drive, so
don't know if there are other issues.

If that works, you're up against the fact that the way most people
have their system set up, what you want is impractical.
You'd have to set up BIG partitions that match ALL the ones on your
internal drive and clone them to the external HDD.  May not work
unless you swap the drives before cloning, make it boot, then swap them
back.  Still may not boot from usb, but if it booted internal, swapping
the drives back should still boot.  What's left on the external drive
could be used for whatever it's currently used for.
You still have a synchronization problem.  You can copy files from the
internal to external drive, but programs won't work that way.
You could get around this by using an image backup program like acronis
to keep backups, then restore a backup after swapping the drives.

Compounding all this is that acer may have added one or more additional
The default install of windows7 puts a small partition before C
that screws up the drive mapping when you're cloning drives.
Unless your partitions map EXACTLY the same, restoring an image
backup still won't boot.

I solved the problems by using linux gparted to partition the drive
BEFORE installing win7.  I have a 25GB C drive that contains all the stuff
that must be imaged to work.  The rest (D:, E:) is just files that can
be copied.
My full backups of C fit on a DVD.  Doesn't take long, so I do it
If, like most people, you  have one HUGE C: partition, what you want
will be impractical.

If downtime is expensive, I'd suggest you buy another drive and clone the
internal drive to it.  Make it boot internal, then you have the option
to swap it in and restore a recent backup when your internal drive fails.

Re: How to create bootable USB external hard drive?

C.M. Burns wrote:

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Apparently it can be done:

Re: How to create bootable USB external hard drive?

On 04/07/2011 12:01 AM, larry moe 'n curly wrote:
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Windows is *not* designed to boot from a USB drive but if it's seriously
hacked it can.

However the comments  I've seen from people who've done it...say
it's too slow to be of much use and it was way more trouble than it's
worth to do so.

The smart thing to do is get an eSATA drive...
with SATA far as the OS is concerned ...there is no distinction
between internal and external

Re: How to create bootable USB external hard drive?

C.M. Burns wrote:
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To boot from an external USB device, the computer BIOS must
have a code module for that to work. Modern computers can
boot from USB, so they have the necessary code. Some older
computers, don't have that code.

In some cases, the option to boot from a USB device is
most obvious, if you press the function key that triggers
the popup boot menu. On my current computer, pressing F8
as soon as the first BIOS messages start to appear, brings
up that BIOS-supported menu. In there, I can see my USB
flash stick listed when it's plugged in. On another computer,
the popup is triggered by pressing F11, so the key varies
a bit, from brand to brand. While the choice of F8 might
seem to conflict with the need to get into Windows Safe Mode,
there is still time to press F8 a second time, if that is
what I want to do.

The first generation of BIOS USB boot code, made explicit
mention of various kinds of emulations. USB floppy, USB HDD,
USB ZIP or the like. With that code, you might end up having
to select the flavor of emulation you wanted to try. That might
have something to do with an expectation about file system type,
such as FAT12/FAT16 versus FAT32 or NTFS.

My current motherboard, makes no mention of those emulation
flavors, and it "just boots".


On the Windows side, there is a problem with older Windows, where
part way through a USB boot up sequence, the USB bus is disconnected
(as the driver initializes) and further file loading stops. The
search term for a fix for this is "Boot Bus Extender". There have
been a few recipes posted on the web, which basically change the
status of USB such that it starts earlier in the booting process.
The idea behind this, is so that the USB bus won't be interrupted
half way through the boot.

Without those changes, the boot won't finish.


One way to achieve the desired results, without setting up boot
bus extension, would be if the 1TB drive could be removed from
the USB enclosure and installed inside the computer. That
would give you the "spare drive" you desire. If you start with
an empty enclosure (the kind you add a raw drive mechanism to
it yourself), that allows you to easily pull the drive later,
and install it inside the computer. Enclosures like this,
exist for both IDE and SATA hard drives (I have the IDE version
of this one).

Then, you'd investigate backup software, with "bare metal recovery"
capability. It would come with a bootable CD or DVD, to be used
in the event that the original drive died.

If you set up a couple partitions on the external drive, like this

     | Room for C: | Data partition holding backup |

then, while the computer is in good running order, you make backup
images to the data partition. In the event the computer fails,
you remove the raw drive mechanism from the USB case, and install
it inside the computer. Then boot with the backup software CD.
It will ask you what you want to do. You then, restore the backup
image from the data partition, to the "room for C:" partition, which
you've carefully made the right size. On the next reboot, you
boot from "Room for C:", as long as the boot flag is set active and
so on.

You should be able to test this, in advance of the disk failing.

In terms of Windows activation, Windows uses a weighting scheme.
A change in the boot drive, by itself, should not be enough to
trigger an activation request. So if you had to restore in the
manner described above, that should work without a problem.
Windows places more weight on the things like the MAC address
of the network interface on the motherboard, as that is a better
indicator a new computer is involved. If you'd made several other
hardware changes, and then restored to "Room for C:" and tried
to reboot, you may be prompted to activate again. (Scroll down,
to see the table of hardware checks.)

One reason I like the "empty enclosure" concept, it is offers
me more options as to what I can do with the drive I bought.
There are many enclosures to choose from, and if you look
at the Newegg listings, you can spot the good ones with mainly
positive reviews.

As long as you have the option to boot a backup software provided
recovery CD, you don't really need to boot from USB.


There is an even faster way to do this. But it requires a second
OS, so you can make a sector by sector copy of the internal C:
to the external drive. A program such as "dd" can do that for you.
You still need a drive enclosure, which you can pull the drive
out of and insert inside the computer, but it eliminates the need
to buy "bare metal backup software". A Linux LiveCD like Ubuntu,
is an example of a platform you could use while making the copy.

             +-- copy via "dd" in Ubuntu --+
             |                             |
     +--------------+             +--------------+---------------------+
     | Internal C:  |             | Enclosure C: |  Other data...      |
     +--------------+             +------------------------------------+

When the emergency happens, you still have to remove the hard drive
from the enclosure, and install it inside the computer. But then,
there is no backup software step involved in the process. The only
problem with this idea, is Windows will alter the VolumeID of the
external C: image, when it detects two partitions with the same

Note - when you move the external C: inside the computer, make sure
the internal C: is *disconnected* for the first boot cycle. Once the
external one has booted at least once, on its own, you can
reconnect the connection to the original drive if you want.
When you clone a boot partition, such as I'm suggesting in this case,
you don't want the original partition to be present for the *first*
boot cycle. After that, it's OK to reconnect it. All it needs,
is one chance to boot on its own.


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