LVM - or another alternative to expand the /home directory as well as MySQL

I have 3 200GB dives hooked up but am only using one at the moment, I've heard that if I go with LVM, all three drives basically become one and when one fills u it spills over to the next but when I clicked the LVM button in Virtualmn pro,it told me that everything would be wiped from the drive (I assume that means reinstalling the OS, AS well as any backups of the sites to the server. Is this true? Is there an easier way to use the other two drives for spill over by linking them somehow to home or bin or whatever is using a lot of space on the original drive? Or must I start over. And why would thee be a LVM button in virtualmin pro if you lose everything and have to reinstall the OS WHEN you may not like the way that virtualmin pro does it's LVM setup and you tweak it from suse 10,0 setup. Im just looking for an easy way to increase my /home directory onto the other drives without having to make a complete server backup, or am I stuck making the backup then restoring. I've GOT SOME 400GB external usb drives that were bought for backups but their terribly slow to read and write going through even 2.0 usb ports. So I dont have them hooked up anymore,and gave them to a friend to "borrow" for his photography business storage needs, until i DECIDE what to do. I can also add 2 more drives if i want to and run them on the SATA cables as well as get some pci cards and run 2 per card with 5 open pci slots,s o I could get a lot of storage internally, but that doesnt solve my more immediate problem of LVM and will it wipe out everything, OS, users, /home directory etc.I've got one of my own sites thats already up to 100GB because of the software repository that i LIST FOR OTHER CMMMERCIAL, DEMOS, SHAREWARE and freeware files that I storeon the disk as well as a huge mysql database to go withit.

Almost all the sites on my server use a MySQL database (onr ot more) , and some of them are huge, so expanding any space allotted to wheregver mysqk id storing it's dta would be a plus in the information. department as well.

Any suggestions.

Thanks for your help so far.