What is the size of the drive you added?

The drive I added a 3-4 years back was a WD caviar 120gb which gave me a total system hdsize of 160gb. Like I said I'm not sure which drive is going, the orginal 40gb drive or the 120gb drive. Either way, I have a new Seagate db35.5 320gb on the way and will be wanting to copy my existing recordings from the 2 drive system to 1 hard drive. Could u point me to the correct guide to use?

You can just do the guide set to replace one drive with one drive, but when you specify the original drive in the command, just put a space and the location of the B drive. So the command should look something like this, with X and Y being the original drives, and Z being the new drive:

Another question. Since i'm backing up 2 tivo drives into 1 new drive, when i look at the commad in the guide of mount /dev/hdw1 /mnt then the backup command of mfsbackup -f 9999 -1so /mnt/backup.bak /dev/hdX /dev/hdy this is going to backup the orginal tivo a and b drive to my pc's fat32 drive which is fine. Once this is done, can I remove the pc's fat32 drive so I can have room for the New drive(hdz). Is the pc's fat32 drive needed to restore the backup on the new hdz drive? I think it is since the command just before the mfsbackup/mfsrestore is "mount /dev/hdW1 /mnt" (hdw1 is pc's fat32 drive) Just wondering how to do it since I have 4 IDE ports. 1 for cd rom, 1 for pc's fat32, 1 for orginal tivo a, 1 for orginal tivo b drive. What do i need to do (remove) to restore data on new drive hdz? Is the pc's fat32 drive just thier to make a backup for future use's if needed? I'm thinking I can just remove it to put in the orginal tivo a and b drive's with my new larger drive. Is this correct

Yes, you can first make the backup, then shut the machine down, and then do either a copy to the new drive (using the code I gave you above) or you could just restore the backup to the new drive.

Ok, I was able to execute the command line you gave me above. I put new drive back in Tivo, and it booted to normal and shows the correct recording capacity.
What I want to do and have not be successfull is to keep the existing recordings from the orginal tivo a and b drives. I'm following the guide to do that but I'm getting a "Restore failed: Backup target not large enough for entire backup by itself." I'm not understanding this error. The weakness boot cd reports the correct size's on the drives. (Orginal Tivo A, hdc, 41110 MB)(orginal tivo b, hdd, 120034 MB) (new drive, hdb, 320073 MB). After I issue the backup command,
"mfsbackup -Tao - /dev/hdc /dev/hdd | mfsrestore -s 127 -r 4 -xzpi - /dev/hdb" It reports source drive is 40 hours - upgraded to 176 hours, uncompressed backup size: 151681 megabytes. Restore failed: Backup target not large enough for entire backup by itself
The new drive is double the size of the uncompressed backup. The target drive is the /dev/hdb in my string above if I'm reading the code correctly. What could I be doing wrong?

Right - the problem isn't the total capacity, it's due to the way the partitions work. You really can't collapse two drives into one and save recordings.

Ok, thanks for all the response's. I may end up transfering the one's we want to keep to my other tivo thru peer to peer(that will be painfully slow, then put the upgraded drive in. Thanks again for all the support.

Right - it's slow, but you can just leave it overnight . . .

Any reason why I can't put my 2 drive's from one tivo into my other tivo B? Both are same models, series 2 tcd540040. I did try putting the 2 drive's in my other Tivo but it did not finish booting to tivo central. It went to the welcome screen, then the almost their screen for a while, then screen goes blank and tivo shuts off after 2-3 minutes. I put the orginal HD back in and works fine. Any ideas?

You can move two drives from one TCD540040 into another, but after the move, you have to choose 'clear and delete everything' from the system reset menu.