Watch out – lvmcache doesn’t support snapshots yet! I discovered this when my backup system tried to create a snapshot of a filesystem to back up after I enabled lvmcache on it.
I removed the cache pool logical volume (disabling lvmcache for the volume) using lvremove, and will re-visit once lvmcache’d volumes have snapshot support (since snapshots are very important for consistent backups).
Background on lvmcache – it is a new LVM feature that uses dm-cache to cache blocks for slower storage (like a HDD) on faster storage (like a SSD) for faster access.