Here's how I do it....
Pre-HR34:
HR21 #1 - FOX, CBS, Showtime
HR21 #2 - NBC, ABC, HBO
HR21 #3 - USA, TNT, Discovery, History, BBCA, Misc
HR21 #4 - Movies + OTA Backups
HR24 - NASCAR Races (Not Saved), Comedy Central, Animal Planet, XD, SyFy, BBCA
Post HR34:
HR34 - ABC, NBC, FOX, CBS, SHO, HBO, MAX, BBCA, History
HR24 - COM, Animal Planet, XD, SyFy
HR21 #1 - USA, TNT, Discovery, Misc
HR21 #2 - NASCAR Races (All saved)
HR21 #3 - OTA Backups
HR21 #4 - Movies
All of them have 2TB drives (some internal, most external) except my HR34 which has 9TB.
I keep a spreadsheet that is setup so that each DVR has its own sheet and on that sheet are the SL's for the DVR. I keep track of what is airing, what is on hiatus but returning and what is on hiatus but may/may not come back. The spreadsheet is setup in "Numbers" on my Mac and shared in the iCloud so my iPhone and iPad have updated copies.
Knowing what nets are on what units makes it easy to schedule a recording using the iPhone or iPad app.