Setting up an LVM cache on an SSD can supercharge LVM.
Or, "You have LVM running on one box and an external drive, also running LVM, with the same volume group name - how in the hell do I mount the external drive?!"
If you find yourself in a position in which you're running Arch Linux and your file systems are based on LVM, RAID, or both, and when you upgrade your kernel your system won't boot because the kernel isn't running the lvm2 hook, here's how to fix it. I just used this fix on my primary server and it worked like a charm.
raid lvm fix boot kernel upgrades initramfs arch-linux linux howto sysadmin
How to get human readable output from the LVM software on a linux machine.