I see in my entire life databases having more performance because are using raw devices (disregard what the dumb people says in tongues without any proof).
What I've tested
Linux and FreeBSD Virtual machines have a significant increase of I/O performance.
What I didn't tested
Windows VMs (well windows do a shitload of I/O, probably it's a good idea if you're into this crap)
BSD VMs (not yet)
Resizing (I don't know if it's possible, I'll test later and update this post)
- Create the LV that will be used (lvcreate -L size -n name_of_lv name_of_vg)
lvcreate -L10G -n myvirtualdiskLV rootvg
- Format the LV into raw vmdk (VBoxManage internalcommands createrawvmdk -filename name_of_the_reference_file -rawdisk /path/to/LV)
VBoxManage internalcommands createrawvmdk -filename /lvs/vms/myvm/linux.vmdk -rawdisk /dev/rootvg/myvirtualdiskLV