How to mount disk on centos 6.4 KVM server

I don't see that filesystem is full. But OK.

Good news is that you are using LVM, so, you can easily expand and move anything.

There are two ways to expand your space:

A. Provided expanded vda

You must expand LVM physical volume, volume group, add it to the logical volume and then expand linux filesystem

B. Provider attached new disk, (like vdb)

You must create LVM pv, add it to the vg, add space to the lv and then expand linux filesystem

Both can be done on the live system.

If you have graphical server running, you can do it system-config-lvm GUI.

For complete answer, please provide more details like:

partprobe
df -h
fdisk -l
dmesg
pvs
vgs
lvs
mount

and tell from which OS you connect to the server.