Glad you are having at least less problems.
About the 140MB, that's only an approximate maximum. Only some KBs are new. About 65MB are from the previous database. So the 140MB I mentioned is "read+write", and half of it could be only a simple "move to new folder" action (which doesn't require a full read + write operation, so it would be much faster than the rest).
My suggestion would be to have / make a backup of your data, and then run the relevant HDD test tools (from the respective manufacturers, but not all of them provide those type of tools). After that, perform filesystem checks (chkdsk / scandisk with fix).
Finally, if you find problems again with Avast, you may want to try the removal utility of Avast applied for each and every version you ever had installed, under Windows Safe Mode (although, if I understood correctly, the only version you have *ever* installed is Avast Free 6.0.1289). Once removed under Windows Safe Mode, you would try again installing in the second HDD, and reboot immediately. Of course all this would be relevant only if problems arise again with Avast, and if you would want to compare the situation between the installation in the first or the second disks.
If you have any other problem or comments, please don't hesitate to come back.