My late 2009 iMac began showing signs of hard drive (HD) failure including applications loading slower, media reading errors, and increasing number of pinwheels (beachballs) showing up. I had already replaced this iMac with a newer Mac for work, and the 5 year-old iMac had been delegated as a media server and second monitor for my gaming PC. One of the reasons I chose the iMac was for its extended life as a high-quality 27-inch monitor using DisplayPort. This target display mode feature requires a running OS which meant I needed a working drive booting OS X.
The big drawback of an all-in-one is the increased difficulty in replacing the internal HD. Opening the iMac and replacing the HD with an SSD is an option, but I didn’t want to spend resources on an already replaced 5 year-old PC. Instead, I used what I had available: an external 2 TB Western Digital My Passport Studio FireWire drive to boot OS X.
How to tell if your Mac has drive read/write errors
- Identify an application that is loading slower, or frequently causing the pinwheels to show up.
- In Applications (or Launch Pad) and inside Other (Utilities) folder, open Console.
- Select “Clear Display” and make sure “All Messages” is highlighted under “System Log Queries.”
- Use that application you picked in step 1 and watch the console. If you see, an I/O error on your disk (such as disk0s2) as seen in the screenshot then there’s likely a problem related to the hard drive. The console may include other errors related to the application.
Other issues may cause your system to slow down including limited memory, a rogue application, or the OS drive is near maximum capacity. In my case, the drive had been exhibiting increasing number of read/write errors in several applications including Chrome and iTunes. My drive also happened to be on a recall list in 2012 so I had been expecting to replace it.
Using an external drive to boot OS X 10.10
Naturally, it’s best to select a drive and port fast enough to handle the intended tasks. More recent Macs have Thunderbolt or USB 3, but the only ports on a 2009 iMac are USB 2 and FireWire. Since FireWire 800 is faster than USB 2, I went with my Western Digital My Passport Studio FireWire drive I had on hand. I don’t recommend using USB 2.
I won’t go over the details on how to install OS X 10.10 on an external drive. There are good examples with screenshots all over the web, and for anyone with experience installing a clean OS on a PC, the process is very easy.
Quick OS X 10.10 external drive installation steps
- Backup the current HD. I used Time Machine.
- Move existing data off the intended external boot drive. Moving a TB+ of data may take several hours.
- Use the OS X 10.10 Yosemite Installer (available on Mac App Store) to install to the external drive (see Show All Disks) and select Time Machine to restore documents and applications.
After I was up and running on my external drive, I noticed faster load times without the pinwheels. As a precaution, I reformatted my internal HD with secure-erase. I also needed to juggle my iTunes media around manually since my drives changed sizes and didn’t all fit as before.
My 2009 iMac should continue working as a media server and PC monitor for several more years.
Update: The old iMac was retired in January 2016 due to graphics card death. I recycled the parts in May.
iMac is a trademark of Apple.