[linux-lvm] failed to install lvm

[ramsis farhat]

hello.
I'm in a training and i have to install lvm on an existing system with 2 disks. For the moment i'm working on a virtual machine.
The first contains sda1 (boot) sda2 (/) and sda3 (swap)
and the second sdb contains nothing.
when i create a pv on sdb and a group with sda1, sda2, sda3 and sdb, the system falls down?
What should I do?
Think you for your help