Until recently, Series 3 Tivos have been considered to have a capacity limit of 2TB. As I understand it, that has been a two part limit:

1) The system cannot handle a partition in excess of 1TB size.
2) Tivoapp cannot handle an mfs address space greater than 2TB

Recently, in a software update (apparently it's not specifically known which one), Series 3 units had the 1TB per partition limit removed. Just the other day, I upgraded a TivoHD to a 2TB drive simply by installing the image and expanding the drive.

Has anyone tried to upgrade beyond 2TB (in actuality(technicality) 2TiB) with a recent software version? I am wondering if the other limitations might also have been removed.

I'm considering trying it myself. I'm one ESATA enclosure away from having what I need to try it, on either an original Series3, and a TivoHD. My understanding is that the Series3 has a 32bit MFS and the TivoHD has a 64bit MFS, which could very much make the difference on whether this is possible or not.