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I have an older laptop that I want to use as a simple media server on my home network. I would like to avoid using the internal hard drive except for booting (BIOS does NOT support booting from USB).

My thought was to mirror the hard drive (currently has current install of Arch Linux) onto the flash drive and then after booting switch over to run everything from the flash drive.

I read the following article about using a RAM disk (HOW-TO: Boot OS into RAM for speed and silence) but ran into problem because the USB subsystem does not seem to be initialized soon enough (I create root and home paritions on the flash disk and modified fstab to pick those - didn't work).

Any thoughts?

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Storing the bootloader, kernel and initrd on the hard disk and mounting only partitions on the USB disk should work. What exactly did you try, and how did it fail? – Gilles Sep 19 '10 at 11:36
It sounds a bit like you're trying to get a similar benefit that you'd get out of booting from an SSD. I've heard of huge speed boosts when running the operating system from the SSD. – Firefeather Dec 16 '10 at 16:27
Why can't you initially boot off of a live CD/DVD? – MaQleod Jul 16 '12 at 3:21
up vote 1 down vote accepted

My suggestion would be to install the boot partition containing a bootloader (I like extlinux), your kernel image and your initramfs to you hard disk.

Then you configure either the initramfs to mount your root partition (which is on your usb drive) or you add the partition as an argument for the kernel in the bootloader configuration. The latter is simpler to achieve, just add something like "root=/dev/sdb1" to the kernel arguments, for a root fs of the first partition on the second hd. Also, you won't need the initramfs if you don't use one already.

Both approaches results in something virturally identical to a boot from usb, but the initramfs approach lets you go (further) to town with lvm, crypto or exotic filesystems om the usb drive.

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This is pretty common in the reverse case, with booting form a usb key to unlock an encrypted internal hard drive. Just check any guide for encrypted root partitions or root partitions on lvm, and reverse the devices. – Erik Moen Jan 8 '11 at 18:02

You can also use a CD with the bootloader that boots up the computer from the USB disk. This way the CD is only used when you startup the computer and after loading the kernel it will use the USB disk only.

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One idea may be to use a virtual machine copied to the USB drive.
That way, usage of the main hard disk should be minimal after the VM started.

It might also be a good idea to use a minimalist Linux distribution, for both physical and virtual computers.

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Definitely an option. I am a little worried about the overhead of running a VM though. – Jesse Sep 18 '10 at 18:59
The VM overhead should be very minimal, maybe even unnoticeable, compared with that of running the OS off the USB drive. – harrymc Sep 18 '10 at 19:41

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