This concept works just as for an internal hard drive. Although, USB drives seem to not remain part of the array after a reboot, therefore to use a USB device in a RAID1 setup, you will have to leave the drive connected, and the computer running. Another tactic is to occasionally sync your USB drive to the array, and shut down the USB drive after synchronization. Either tactic is effective.
You can create a quick script to add the USB partitions to the RAID1.
The first thing to do when synchronizing is to add the partition:
sudo mdadm --add /dev/md0 /dev/sdb1
I have 4 partitions therefore my script contains 4 add commands.
Then grow the arrays to fit the number of devices:
sudo mdadm --grow /dev/md0 --raid-devices=3
After growing the array your USB drive will magically sync 
USB is substantially slower than SATA or PATA. Anything over 100 Gigabytes will take some time. My 149 Gigabyte /home partition takes about an hour and a half to synchronize. Once its synced I do not experience any apparent difference in system performance.
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I added GOS back to VirtLinux, in its new beta state. It appears stable, and is up to date as of 1/21/2008. Overall I like the look and feel of the system, and may end up using it as the host OS on my laptop. I anticipate much to come from this Ubuntu based Linux distribution.
http://www.virtlinux.com/downloads.html
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I use this blog to talk about my computer experience, and have stuck rather strict to this theme, but I must digress slightly. First and foremost Wikipedia is the 9′th most visited website in the world according to Alexa; exposure is king. For years there has been a debate on the Brown’s Gas information to be included in the online encyclopedia, with not much progress being made. Then I decided to pull together all the documents I’ve collected over the years, and viola, a properly sourced encyclopedic article. It really clarifies many misconceptions about Brown’s Gas. It’s a well rounded, and thorough article covering design, efficiency, and an assortment of popular claims.
http://en.wikipedia.org/wiki/Oxyhydrogen#Brown.27s_gas
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The new method of mounting a guest server directory via sshfs, and creating the .vdi image directly on the server works just fine. ReactOS is now confirmed to be working and is now available for download. I will keep its version reasonably up to date.
http://www.virtlinux.com/downloads.html
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