I am wondering if a portable hard drive (such as the Seagate Backup Plus Portable Hard Drive or the WD My Passport Portable Hard Drive) will work as an external hard drive for my DVR
Good question Nick, in general any hard drive that meets the following requirements will work.
1: It has to be a minimum of 500gb memory, but no more than 2tb memory.
2: It must be a single platter drive (the majotity of external hard drives are)
3: It must be USB 2.0 compliant (almost all modern EHD's meet this standard)
For an example of an acceptable hard drive here is the amazon page for an external drive I use on one of my testing boxes: https://www.amazon.com/Seagate-Portable-External-Photography-STDR1000102/dp/B00H4XH586