My current setup has 3 hard drives for sharing data. My 250 GB drive is approching full I decided that to get another one. The new drive will be used for the same type of files (video). I have everything organized into folders such as TV, Movies, etc. I would like to add the new drive and make it a seemless as possible. The two drives must be seen as one. I've tried looking around for info on RAID and LVM to find which is best for me. So far they sound extremely similar as to what I would use them for. But, everything I've found leads me to believe that I would have to backup all the data and format the drive to set it up for a RAID/LVM setup. So, is there a way to set up either RAID or LVM wihtout formatting a full 250 GB drive? Also, is there a reason I should choose LVM over RAID or vice versa?

Both RAID and LVM must be set up from scratch so unfortunately a backup/format/restore is nessesary if you want to ether. If you just want to add more storage space a LVM would be what you want. with RAID you could make both drives appear as one but once they are full your back to where you are now. with a LVM setup you can go on adding drives into it as much as you want, plus you can resize LVM partitions without a lot of trouble. The main use for RAID should really be for redundancy/data security not so much for creating larger drives.

Thanks for the quick reply I guess I'll actually have audit my system and see if I need all this stuff. Hopefully that will produce enough room to back it all up.

It doesn't have to be RAID or LVM. You can have both.

My current favorite for a setup is to put an LVM on top of a 2-disk Raid0. It's blazingly fast (hdparm -t = 105MB/s using PATA drives) with exceptional storage flexibility.

Setting it up is fairly easy. You set up swap on both drives, make a Raid1 for /boot and put everything else into a Raid0 set up as an LVM with logical volumes for /, /home and /var or however you want to divide things up (or not).

It's really that simple to do and you can easily resize the logical volumes as your needs change.