To solve her specific mirror-to-SSD migration problem, she actually needed to use lvconvert to split the mirror, but she kept the concept of lvmerge in mind for the integrity of the data.
Days passed. The resynchronization finished. The data was now identically present on both the old clunky drive and the new SSD. The system was now running in a "mirrored" state. lvmerge
Once the merge was complete, the snapshot volume disappeared (as it was consumed by the merge), and the original volume was restored to its pristine state, ready for the next workday. To solve her specific mirror-to-SSD migration problem, she