DRDB

DRDB: refers to block devices designed as a building block to form high availability (HA) clusters. This is done by mirroring a whole block device via an assigned network.

MPIO

Novell has a simple howto for MPIO. I also found more details and how to do failover tests.

I've heard that LVM manages physical slices by device name (/dev/sdX), not disk ID and that since multipathd increments device names (/dev/sdc becomes /dev/sdd) that LVM gets confused and requires a vgscan and vgchange -a y between a remount. I'll try for myself sometime.

Update QLogic has a forum post on failover and LUNs discussing the redundant devices and more information about what they mean.

VirtualBox

VirtualBox is interesting. Ubuntu should make it easy to test.

Google Data Center Power Usage

Data Center Efficiency Measurements