Restore time differences between full database dumps and separate schema/data dumps

Hello,

I recently attempted an upgrade on one of our servers from 8.2.6 to
8.4.1. I created two separate dumps for the database, separating the
schema and data. I did separate dumps because I need to expand the
size of a column in one of the tables.

After the schema restore, everything was going seemingly well until I
started the data restore. The data seemed to be restoring at a
reasonable rate, considering the database is in excess of 17GB. After
approximately 30 minutes, I checked the size of the data directory to
try to estimate the total restore time - it was less than 1GB. An
hour later, the restore was stopped, and disabled autovacuum in
postgresql.conf; this made no change. Two hours later or so, the
restore peaked at 2.2GB, and the upgrade was aborted.

I copied the schema/data dumps to a testing machine so I could see how
long the restore would have actually taken - in 24 hours, the data
directory was just shy of 4GB in size. Searching the documentation
and archives, I don't see any clear explanation.

When schema/data are separated, is the restore treated as INSERTs?

Is there something else obvious I am missing, or that I can check?

Regards,

--
Glen Barber