John Gruber’s beneficially paranoid advice about maintaining recent and complete backups.
March 16th, 2010
John Gruber’s beneficially paranoid advice about maintaining recent and complete backups.:
“Every hard drive in the world will eventually fail. Assume that yours are all on the cusp of failure at all times.”
I still rely on TimeMachine for everything but it’s probably time to buy an external disk and at least do a full monthly on it.
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My favourite: “But let’s stop talking about “backups.” Doing a backup is too low a bar. Any experienced system administrator will tell you that they have a great backup plan, the trouble comes when you have to restore.”
http://www.joelonsoftware.com/items/2009/12/14.html
I learned an interesting thing about disk failure in my stats class. Statisticians use exponential decay functions to model the distribution of the service life of many things, including hard disks. According to this model, the expected future life of a working drive is entirely independent of how long it has already been in service. Assuming equal mean time between failures for both my internal drive and external drive, each is statistically just as likely as the other to fail in any particular time frame – even though the internal drive came in my PowerBook when I bought it in 2004 and the external drive was purchased just a year ago. At first glance this seems to mean that making a backup provides little protection; however, the chance that both drives will fail so close to the same time that you do not have a chance to replace and recover is small. Each additional backup reduces your risk by an order of magnitude.