I dont see any reason why one should use lvm in xen guest. The whole idea of using lvm is to have the ability to resize disk size easily and resizing a xen guest can be done easily without using LVM. Actually, having LVM in xen guest complicates the process of resizing… You can google [...]
I got inspired by the 10 commandments for system administrators from http://www.linux.com/feature/44315
This is my list:
1. Be WARY about COST CUTTING.
(cheap hardware, cables, labour)
2. KNOW THE NETWORK well.
(keep network, routing diagrams, track public and private IP, label cables if necessary)
3. ESTABLISH STRONG SECURITY POLICIES in the system.
(Security Access, File Permission, good password choice, encryption, SetUID, LDAP, [...]