View Full Version : Bit-Rot and Superduper! smart updates

07-12-2014, 12:37 PM

I have read recently that data left on HFS+ external hard drives for a couple or more years are in danger of corruption, through "bit-rot", or perhaps a magnetic weakening or disturbance over time. I have a large collection of music on an external Firewire drive that I smart- update to a clone back-up drive about weekly, as I gradually add to and edit my iTunes music library. But I worry that stale sectors of the primary media drive may get corrupted after a few years and that that corruption may be automatically copied over to the target back-up drive in my periodic smart back-ups. Or would Smart Update not copy this bit rot corruption since there is no change in the date of data modification? I gather a ZFS formating would help detect and possibly avoid this kind of corruption, but that is academic for now in Mac-world.

Any hard drive maintenance/ hygiene advice on avoiding bit-rot, or other magnetic corruption, over many years would much appreciated. I just bought a third hard drive that I plan to alternate with the older target back-up drive (perhaps once a month) to give me additional redundancy. Should one do a complete erase and copy procedure to clean and reload the data on older back-up drives every few years?

By the way, should external back-up drives always be formatted as HFS+ (Journaled), even if the original drive was not journaled?

Thanks for your help.


07-12-2014, 01:52 PM
To answer the last question first, I always format drives journaled. Always.

For the first, I can't think of a single time I've experienced "bit rot" with existing data on any drive that didn't explicitly fail (that is, a quantum bit-flip, as opposed to a sector going bad). So, I do what I recommend in the User's Guide - I maintain multiple backups. It's vanishingly unlikely that the same file is going to go bad due to drive failure on multiple drives - and nearly all my backups are on RAIDed (redundant RAID) drives to boot.

07-12-2014, 05:28 PM
Thanks so much, Dave for your very helpful, super speedy reply. Wonderful service, as always. I'm glad to hear you don't worry much about "bit-rot"--probably a rare, over-hyped disease that should be the least of my concerns with so many other more likely perils out there. The second BU drive will definitely help me sleep better.