Joshua C writes:
I've been reading your site for years and following a modified version of your backup strategy (no offsite, just a drive in a firebox away from the computer).
My current RAID enclosure was getting flaky so I decided to replace it. The problem was temperature and fan related so I was migrating the drives to the new enclosure
I knew I would have to reformat but I've got two backups so that's OK. That is until I accidentally installed my clone drive as one of the drives in the RAID without noticing. Bang! My original and my clone were gone. My heart stopped. This RAID contains ALL my image files.
But since I have another backup I am rebuilding as I write this. One human error could have wiped me out. Following your guidelines has kept me going.
MPG: See the backup pages for critical backup strategy discussions.
Two backups are far better than one: with one backup, a failure means you’re down to a single master copy, possibly out of date. With two backups, loss of one backup means you’re down to one remaining master copy (possibly out of date), as with Joshua C.
Anything less than three complete backups should be a source of uneasiness for anyone who values their data. For starters, spreading the risk (physical risks, bonehead mistakes, out of date backups, drive failures, splitting across sites, etc).
Time Machine backups should be considered strictly a nice-to-have additional redundancy for short term protection. It does not count for the “three”. For one thing, Time Machine has had historical bugs that left data unprotected (and I don’t trust Apple anymore, what with the massive increase in bug count in Mavericks), for another it is unbootable, and it’s also typically subject to the same physical risks. Also, if it fills up, you’re out of luck until something is done, whereas clone backups used properly can never fill up provided they are as large or larger than the original (e.g. some amount of data on a 4TB original can never overflow a 4TB clone backup).
Here is a good general purpose backup drive suitable for all Macs. 4TB or at least 3TB capacity recommended.
You do NOT need RAID for backup; it is far better to have two independent drives than a RAID mirror. RAID is a fault tolerance or performance solution, NOT a backup solution.