I do photos, not videos, so my library is only around 500 gig. That said, do you really need 1.5TB of active working files? Why not just keep your last few months of projects on the laptop and leave the rest in your well backed up archive? Having silly little boxes hanging off your laptop is so inelegant.
Even if you need all that on a laptop, the MBP will take 2 1TB drives so you can have it all that way.
If you really need massive amounts of fast storage a laptop is not for you. My desktop is a PC with 12TB of internal storage on sata6gb ports. If I fill that, I can bump it to 15TB for another $140 and 10 minutes of work.
Not everyone works the same way, so your 'ideal' setup may not be best for everyone else.
Suggestions:
1. Make sure you get minimum 7200 rpm drives for USB3
2. Consider ($$$) SSD external storage, any external bridge will be considerably slower than your internal SSD
3. Use a RAID device for larger external transfers (I have been happy with G-Tech portable, and Stardom desktop devices)
4. Internal 1GB drives for the MBP (that you do not have) are 5400 rpm only.
All of these options are a compromise, it depends on which aspects suit your circumstances.
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The G-RAID mini gives 1TB in RAID-0 configuration, is bus powered and uses 7200 rpm drives.
Currently available with eSATA & USB2, with a USB3 model 'soon'.
OWC make a USB3-eSATA adapter.
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I was following the 'holy grail' of a faster connecting bus (using the Seagate GoFlex series). Having shelled out hundred$ on the Thunderbolt connector & cable, I realised that it was no faster than FW800 using the 5400-rpm drives of the 1.0 & 1.5 TB models. Using the USB3 connection on the new MBA yielded similarly dismal results (around 80 MB/sec for both).
As a result I'm sticking with my older MBP17 & eSATA. The newer interfaces may be faster, but the drives are not.
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My Stardom unit (RAID-0, 3.5" drives) gives speeds close to my 3G SSD, and the G-Tech is as good as an internal HDD using a Sonnet eSATA ExpressCard.
All other options are too slow for (my) use. [I'm happy to leave an external connected for a maximum 15 minutes to an hour, while a job is completed. After that, if I need to move the laptop, ANY external connection is a nuisance.]