I got a new VPS. It's running CentOS 5.5.
The hosting company said some VPS nodes have RAID BBU while some don't.
How do I tell whether my VPS node has BBU or not?
Also is there a way to tell how many and what type of disks my server has?
The only real way to tell is to actually ask your host - they will know what physical server your VPS is on and should be able to provide you with the specs of it.
Since it is a VPS, it will show as having some generic virtual disk and won't really reveal any information about the underlying hardware. That includes disk manufacturers, models, type, RAID configuration - the lot.
First, you would need to know what RAID controller they are using. 3ware/Dell/etc.. Tools such as dmidecode and dmesg should help you learn more about the detected hardware.
Each vendor provides their own tools for querying the controller and what exists behind it. Some are available as binaries which may require root privileges to run.
Unlikely, but if software RAID is implemented the standard
Edit: Ben's answer made me realize that this is a virtual machine. Sorry, he's right. The underlying hardware wouldn't be visable to a guest operating system, just the hypervisor. I will leave my answer as it might help someone searching later.