It’s been a long time since I did anything with the drives in my HR series, but if I recall correctly you can clone a drive to a similar or larger drive and save the recordings in the same machine. If I recall there is a code embedded in the recordings that identifies which machine recorded the content and only that machine can access it.
If it's not content you want to save long term but only watch and delete best option is to add the HR44 and pay the mirroring fee on the HR34 until you view all the content. Saving content on the HR series long term for archival purposes is a bad idea since A- you don’t own the unit and B- hard drives fail.
Is this still true or has it been verified?
I have an HR-21 and I will be upgrading to am HR-24. I was going to use this process to copy the recordings over to the new box, but if this is true, it won't work anyway.