Disk rotation with LVM: almost no downtime

Every so often, data on the home server gets dangerously close to how much storage is available on its disks. That’s when the disk rotation dance starts. First find the disk with the lowest price per GB ― ugh, is it just me or did those prices go up… I wonder why… Then, move the data around. The idea is to remove the oldest (and generally smallest) disk, and to move data from it to the next one in the conga line, so every mount point has more space than before. I leave some wiggle room to leave the most important data on the most recent disks, though. In the past, I used to rsync(1) data across mount points. This required multiple steps and various periods during which no new data could be written. In the last few years, I got into the habit of using LVM volumes for all those disks. On the last dance, I realised that I could use the low-level data replication mechanisms of LVM to copy the data with almost no downtime. tl;dr: extend the Volume Group to the new disk with vgextend(8),…