We recently ran a major compaction across our cluster, which reduced the storage used by about 50%. This is fine, since we do a lot of updates to existing data, so that's the expected result.

The day after, we ran a full repair -pr across the cluster, and when that finished, each storage node was at about the same size as before the major compaction. Why does that happen? What gets transferred to other nodes, and why does it suddenly take up a lot of space again?

We haven't run repair -pr regularly, so is this just something that happens on the first weekly run, and can we expect a different result next week? Or does repair always cause the data to grow on each node? To me it just doesn't seem proportional?