I back up to AC in the cloud, a portable disk drive and a HDD on my server. I do not know if these are incremental backups. I think they are full back ups because I have to go into AC backups on the main drive, periodically, and delete the old ones because of the space that they take.
Here you are talking about a few things. Your .enc AC backups are simply a complete, encrypted and compressed backup of everything AC. It is what you can restore AC from. But, those are always full backups.
There are three major types of backups and another fourth that is rather new technology.
Say you do a full backup of everything on the computer or drive on Monday. On Tuesday you would make a differential backup (everything that has changed since Monday). On Wednesday, you would make another differential backup of everything that has changed since Monday's full backup. So, each day, you would continue to have one backup that contained everything since the full backup. As you can see the first differential would be very small and fast. The next day it would be a little larger and slower.
With an incremental backup it is similar except you continue to make single backups, e.g. Monday is full, Tues is of everything changed since Monday, Wednesday would be everything changed since TUESDAY. So, if you needed to do a restore on Saturday, you would need the Monday backup (full) plus Tuesdays', plus Wednesday's, etc.
With the differential backup, you would need Monday (full), plus Friday's.
So, if you did fulls everyday, you would take longer, take more space, but have safer backups. Differential and incremental are much faster.
Your full backup may be 56GBs. Your incremental may be 128Mbs.
The hard drive on your server would be the quickest to restore but is the weakest backup you can have since it will likely crash along with the hard drive it is on unless it is a separate drive. Many backup programs like Backup Assist will backup the system drive or entire hard drive to a drive on the server and then copy that to an external drive.
Basically, the best backup as far as integrity is the full backup to a non-portable, external drive. Even better if it is Raided but that isn't necessary.
