Welcome to LQ!
In the past what I have done is created an md raid0 and then used the md device as a pv for the vg where i create lv. If you are not wanting to do that, this article discusses using just LVM to stripe (raid0) an LV across multiple PVs.
How do I create a logical volume using Logical Volume Manager (LVM) post installation?
assuming the 5 1TB drives you added are sd[bcdef]
reading that article, it looks that you would, for example, then perform
vgcreate BigVG /dev/sd[bcdef]1
lvcreate -l 100%VG -n BigLV -i 5 BigVG
then make your filesystem on /dev/BigVG/BigLV, mount it and go
You should also be aware of filesystem limitations from RedHat RHEL
. I do not think this will be a concern or problem immediately for you (with RHEL4 or RHEL5) since you are only using ~5TB but should be taken into consideration should you decide to add additional capacity and grow the LV and filesystem later on.