i experienced some thing similar. how do you explain it.

datafile size: 17 GB

log size: 12GB

objective: migration from 2005 to 2008 by the external vendor on site.

i noticed 2005 version is using 2000 comparability level.

so i changed the compatibility level to 100. run consistency check.

as db in full recovery mode i changed to simple recovery mode.

As i knew they going to drop indexes and rebuild and stats update changes to objects..etc.

i truncated the log and set to 5 GB.

My expectation: because it is in simple recovery and log should not grow much.

actual: it has grown to 48 GB.

i could not find the reason why it has grown that big.

how do you explain this?