When it comes to video security storage capacity, I usually suggested 1 Terabyte for the storage on a 4 camera or less system. That typically translates into about 3-4 weeks of data, dependent on the activity. More activity will translate into more hard drive usage. If you want longer, you can either increase the hard drive size (4TB is about $250) or lower the frames per second on the video. More tricks include decreasing sensitivity of the motion and masking off trees and bushes that may blow in the wind causing motion recording.
The hard drive gets filled and then will automatically overwrite the oldest data with new recordings. So you will always have a floating period of time that will remain. Nothing on your part is needed. Just be sure to download any video you want preserved to a thumb drive or computer.
By the way, we always use Western Digital Security Grade Hard Drives with a 3 year warranty as our data storage drive.
Let me know if you have questions. Call us at (773) 529-2779 or email at firstname.lastname@example.org.