While on a few days off at the end of last month I decided to upgrade my DirecTiVo and my HD DTiVo hard drives. In both cases I wanted to maintain my existing recordings and simply add additional storage. I ordered 2 Seagate DB35.3 320 GB and 2 750 GB hard drives. Due to some mixups I actually ended up with 3 of the 320 GB. I started by attempting to upgrade my HDVR2. I used the boot CD available from MFSLive.org. The copying process went just fine, however the TiVo wouldn't boot properly afterward. I posted a note to the current developer of the MFS tools on TiVo Community.
While waiting for an update on the HDVR2 I moved on to the HR10-250. For this TiVo I was going from the original 250+400 GB to the new 750+750 GB. The process took about 5 hours. Once it was complete the TiVo booted fine.
In the middle of this I went to the Fantasy Football banquet. While there I mentioned what I was doing to Travis, he told me he had a broken SD-DVR40. He gave it to me. The only thing not working in it was the original 40 GB HD. I upgraded it to two of the new 320 GB drives. I used InstantCake from DVRUpgrade as a base image. It worked well.
A day or so later I found out there was a bug that was causing the problem with the HDVR2 upgrade. I was able to workaround it and upgrade with the last of the 320 GB drives and the 400 GB from the HR10-250. This was up from the original 40 GB and a 160 GB (using 137 GB).
I now have a total 1500 + 640 + 720 + 250 (Series 3 which will probably be upgraded to 750 or 1000 in the future) = 3110 GB of TiVo storage. Some might say that is a little overkill and they would probably be right.