My hard drive in my iMac died this week.

The iMac is from late 2008, so it’s less than 5 years old, and this is the 2nd drive that’s died; the drive it originally came with was replaced a few years ago already.

Here’s how I diagnosed the issue, and got myself running again.

About 2 weeks ago I upgraded my iMac from Snow Leopard to Mountain Lion, and I immediately started seeing a lot of pinwheeling while in many applications. I ran Activity Monitor (it’s in Applications -> Utilities) and could see that lot of computing power was being used, even to perform simple tasks.

Given the timing, I assumed the upgrade had caused some system issues.

I checked to make sure my Time Machine backup was up to date, and then I completely erased my iMac hard drive, reinstalled Mountain Lion from scratch, and used Time Machine restore to bring my software and data back.

Everything seemed fine for about 2 weeks. Then, this week, I saw pinwheels for an entire morning, and even had to force-shut down and restart my computer a few times.  Normal activities were taking longer and longer. I couldn’t even move a file from one place to another.

Symptoms such as this, especially when they get worse and worse over a period of a few hours or days, definitely suggest a dying hard drive.

Luckily my Time Machine backup was still up to date so I immediately went to Best Buy, purchased a new hard drive, and restored everything from Time Machine to the new drive. Then I installed the new drive into my iMac.

A few things I learned:

• What I think is happening isn’t always correct! My assumption that the pinwheels were from the upgrade was totally wrong, and I should have been more alert to other possibilities.
• Always make sure you have multiple backups of your stuff. Although I was inconvenienced, I wasn’t seriously worried at any point, because I had a Time Machine backup of my entire computer, and a cloud backup (via CrashPlan) of my home folder, and a Dropbox sync of all my company files.  So I knew my files were OK.