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Robert57 07-12-2014 12:37 PM

Bit-Rot and Superduper! smart updates
 
Dave,

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.

Robert

dnanian 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.

Robert57 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.

Best,

Robert


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