Mac users have a wonderful resource called "Time Machine." It automatically backs up and maintains your files in a series of memory-efficient snapshots, allowing you to quickly resurrect a file or -- as I had to do -- recover from a total hard drive failure. It's an integral part of the operating system and it runs without you ever realizing it, doing its essential work in the background. The only time you need to know about Time Machine is when you need to find an older file.
When Time Machine works, it is an amazingly-engineered godsend. But when it DOESN'T work, it's a freaking NIGHTMARE.
You see, sometimes the external backup drive can become inaccessible -- hard drives aren't perfect and neither are their connections -- but if this happens during a critical period of Time Machine's operation, the drive just...hangs, leaving Time Machine in an endless "Calculating Changes" state. If you try to cancel Time Machine it gets stuck in an even MORE endless "Canceling" loop. You cannot access the disk and you cannot cleanly unmount it. You cannot reboot the computer. The disk just sits there...and Time Machine -- along with its bosom buddy Finder -- just keeps trying to shake it, like a dog who won't let go of something gross no matter how many times you chastise it.
I have tried EVERYTHING to fix this -- troubleshooting steps, killing processes -- and the ONLY thing that works is the one thing you're supposed to never, ever do: forcibly turning the drive off. By doing this you risk corrupting all your data, but there's simply no other solution: it's either that or keep your computer on forever while Time Machine keeps saying "Almost done! One more second!"
This used to happen to me at least once a day, when I had the hard drive daisychained through my Presonus Firestudio Project hardware. After I swapped the order and put the hard drive FIRST in the chain, and also changed my System Preferences so the drive is never sent to sleep, everything's been fine...
...until this morning, after a week or so. Had to turn off the drive and reboot. Just like the old days.
I have no doubt that this STARTS as a drive issue (it's an Elephant Storage device) but I can't help wondering: what sort of operating system can't recover from something like this? I know, I know, operating systems aren't perfect, and Mac OS is otherwise beautifully stable...but this problem has been happening since Leopard (and before, if you believe the forums), and nobody has stepped in with a piece of code that says "If external drive will not respond after X minutes, pop up a message that tells the user there's a problem and request direction. If user chooses to stop waiting for the drive to respond, then shut down Time Machine, forcibly kill any processes that are still trying to access the drive, forcibly unmount the external drive, and tell users to set up their Time Machine again and that a reboot of the drive may be necessary."
Yeah, easier said than done maybe. But there is NO excuse for an endless loop that requires drastic user intervention just to turn the system off, especially not when such users might not be particularly computer-savvy.
Time Machine, I love you, but you're too damn stubborn.