10-17-2012
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Join Date: Oct 2010
Last Activity: 1 February 2016, 3:35 PM EST
Location: Southern NJ, USA (Nord)
Posts: 4,673
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I have a continuous Mozy Internet backup so intermediate changes are not vulnerable long, and a usb 1TB hard drive I plug in to each box in rotation to catch it up. The Mozy took 3 days to restore my saved files last time, alone. So, I have no gap.
Now, to do offsite with external hard drive, get extras so the one on site to be written is not the most recent prior copy, like backup tapes. The Internet product is still wise, as it makes the window of vulnerability very short. If you use network not sneakers to move the backup data offsite, you can merge the two. Have a local copy very quickly updated and great for restores, and a remote copy that may lag more, is slow for restores but ensures the data is still online if that center goes down. Disk is cheap, data is priceless. Mirrored data centers can ensure that data is and processing are both in multiple distinct places. A compressed stream of updates both ways can keep them pretty close in sync without slowing either host.
Good old MULTICS had no hard links, and any change rippled up the tree into directory status all the way to the root, so you could find just the modified files with zero effort. Modern file systems and volume managers can support backup systems with similar lists. After the fact new file discovery is slow and loads the system more.