The Western Digital My DVR Expander Hard Drive was recently released so that you can add additional storage capacity to your eSATA port-equipped TiVo DVR. It adds up to 65 hours of high definition recording time or up to 600 hours of additional standard definition recording time, depending on your system and signal quality. Specifically, this system allows you to store more programs on your TiVo® HD or TiVo Series3™ HD DVR (not compatible with TiVo Series2™ DVRs). It seamlessly adds this storage space. There is no need to manage which program is stored where.

There’s an official FAQ located here that answers most of the pressing questions. Here are some of the highlights:

Can I use a My DVR Expander with my TiVo Series3™ or TiVo HD if the internal hard drive has been modified by myself or a third party?
We strongly discourage anyone with a modified internal hard drive from using a My DVR Expander. The combination of a modified internal hard drive and a My DVR Expander may cause the system to malfunction.

Can I use the DVR Expander with more than one DVR or move it from a TiVo® DVR to a different DVR?
No. You cannot move the DVR Expander from one TiVo® DVR to another. All or most of the recorded content from the TiVo® DVR and all of the content of the DVR expander will be lost once the DVR Expander has been formatted by another DVR.

How do I know whether a recorded program is on the DVR or the DVR Expander?
On the TiVo® DVR, each recorded program is stored partly on the internal drive and partly on the DVR Expander.

Can I use more than one DVR Expander drive with my TiVo® DVR?
No. The TiVo® DVR only supports one DVR Expander.

Is the DVR Expander portable?
No, the DVR Expander is not designed to be a used as a portable device or as an attachment to a computer.

What will happen if the DVR Expander is plugged into a computer?
You cannot view the recorded content on your DVR Expander if you connect it to a computer. To use the DVR Expander with a computer, you must first reformat it, which erases all its current contents.

UPDATE - You need Tivo Software version 9.2 to enable the use of this external drive. You can get on the priority list by signing up HERE.

- The TivoCommunity website has a much more detailed “techie” FAQ about eSata Drive Expansion and the 9.2 update.  You can read the full FAQ by going here.