If you follow the instructions the hardware part goes pretty smoothly. Step 1D is the only tricky part. Read the whole bit about how to apply pressure in steps or you might break off a tab.
BUT before you start get kmttg before you start the upgrade and save off your settings:
- One Passes
- Thumbs (Though it seems TiVo might not be using these anymore.)
Otherwise you will be manually be setting them up again. Note in theory One Passes should be downloaded from your TiVo account but if you want to have them today you will need to load them via kmttg.
Next bit is you will probably need to call your cable company and have them push an activate to your cable card even though the host ID does not change.
If you favorited channels you will need do those again manually.
Lastly you will need to reactivate all your apps.
Update: looks like you need to turn auto skip back on as well.
After the upgrade you should find:
Note part of that used space was programs already recorded by my uploaded One Passes.
If 3 TB is a bit tight you should know WeeKnees has options with Bolts up to 13TB and Roamios up the 20 TB