When ever the power goes out or I restart my iMac the external hard drive that is used by Time Machine for backups is dismounted ?

Question

When ever the power goes out or I restart my iMac the external hard drive that is used for backups by Time Machine is dismounted and all backups are gone. I can reselect it and it will start working again, but I am worried if the iMac hard drive should fail will I be left without a backup ?

Answer 1

fzgy wrote:
"Mac OS X can't repair the disk.  You can still open or copy files on the disk, but you can't save changes to files on the disk.  Back up the disk and reformat it as soon as you can."
It's possible a heavy-duty 3rd-party disk repair app can fix it, but they're expensive (DiskWarrior is about $100), and there's no guarantee it can do it.
Am prompted to reformat but I don't have a good understanding of what this means and how to do it.
That will erase it.  See Time Machine - Frequently Asked Question #5.
It sounds very much like the disk is beginning to fail, although it's possible there's a bad port, cable, connection or power supply (if it has its own).
I'd suggest getting a new one, and using it for your Time Machine backups; once you have a good backup there, reformat the old one (and select Security Options to write zeros to the whole drive -- if that fails, you know the drive is toast).  Use it for secondary backups, per FAQ #27.   If it has failed, get a second new one for secondary backups.