Hello, I tried upgrading pg db from version 9.6 to 14 by using pg_upgradecluster command. I freshly installed pg 14 -> ran pg_dropcluster 14 main --stop -> and then upgraded using pg_upgradecluster 9.6 main.
After a successful prompt finished, I checked the database and the size went from originally 20gb (in 9.6) to 700~ mb (in 14) while the disk space available shrank by about 2gb meaning that there is still the 20gb of data. I tried the entire process twice (since I had created an AWS EC2 snapshot for this) and the result was the same.
Is my solution to migrating old pg version to the new one wrong? Before this I tried the same process with around 300mb of data and all of that transferred successfully. If I did not understand the pg_upgradecluster command, what would be the best practice when upgrading pg version with huge amounts of data(could be a terabyte)?