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#1
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question about "bit rot"
I've been thinking about hard disks as long-term storage, and I've realized that magnetic domains on hard disk actually aren't permanent. The field strength decreases by more than 1%/year. So even for a hard disk that is never used, your data on it will gradually fade away. Errors will increase on time scales of years. This is well understood.
As far as I can tell, the only way to prevent this is to completely rewrite your hard disk data once in a while. Every year or two? Very little cogent info about mitigation strategy that I can find. That makes me wonder about SuperDuper smart updates, which just write things that have changed. Things that haven't changed don't get rewritten. So after a while, much of your archive disk data can get stale. Is this a concern? As in, is it smart to do a full up backup every once in a while instead of smart update? Some expert advice would be handy. |
#2
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I take a major OS update as an opportunity to do a full backup, Dan. On top of that, I use a number of backup volumes, some of which are RAID and get scrubbed, to ensure that things are generally safe. Plus, I use online backup... your best approach is thorough, diverse coverage.
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--Dave Nanian |
#3
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Are you aware of any Mac utilities that do disk refreshing? I think there used to be one, called DiskRrefresher, but that's no longer available. There are PC utilities that do this. There was, many years ago, a post about doing disk refreshes in a Unix-based system ... https://larryjordan.com/articles/tec...-disk-storage/ but I frankly think those techniques don't really do what he says they do. It would be nice to see some well-thought-out strategy for long term archiving on hard disks. I realize that's not necessarily the purpose of SuperDuper, but your insights would be welcome. |
#4
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Well, again, the scrubbing does refresh the data (as, obviously, does the yearly rewriting). So, if you consider your NAS-based backups "archival" and have them scrubbed, they seem reasonably safe to me.
As far as there being a good chance that after a decade none will work - I've been surprised that most drives *do* work just fine after a decade, retaining all their data. Which, of course, is no guarantee.
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--Dave Nanian |
#5
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And yes, while MTBF of hard disks is supposed to be about five years, they've always lasted much longer than that for me, at least for mechanical performance. |
#6
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No, that's not what scrubbing does: your NAS usually will offer data integrity scrubbing.
And I'm talking about more than mechanical performance. There's a lot of "fuzziness" in magnetic drop-off, hence the ability to recover data from master tapes that are 50 years old.
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--Dave Nanian |
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