By Graham K. Rogers

Over the last few years, the external rescue disks I have made have been invaluable, getting me (and some friends) out of difficulties on a number of occasions. The process of making self-booting external disks changed significantly with the arrival of OS X 10.7, Lion. Creating such a disk for rescue purposes is almost identical for the latest version of OS X 10.8, Mountain Lion.

Background

I used the Disk Warrior installation several times for preventative maintenance, including when preparing my MacBook Pro for the OS X update to Mountain Lion. It proved its full worth when the hard disk on the iMac I keep in my office went into self-destruct. Using Disk Warrior I was able to rescue important data from the disk mirror it created when I had been unable to start the hard disk using normal means and was concerned about loss of the data. All that I needed was saved ready for a new hard disk when that was installed.

Preparations

The saved DMG file was on the Rescue disk that I intended to update, so I started by copying that to the desktop of my own Mac. I noticed that in the Applications folder of the Rescue flash drive, many of the apps were shown with greyed out icons and a "No entry" sign. I presume that this is due to the updated OS on the Mac being unable to read the older files properly. The disk itself can still start up a computer and with 10.7 running, the apps are OK.

When I checked again after the 10.8 installation was complete, the application icons displayed correctly.

Installing Mountain Lion

The installer was unable to complete the process as it reported that another 3.14 GB of space was needed. I considered deleting some of the files, but used Disk Utility and in a short while re-partitioned the drive which reported 15.67 GB of space was available. I restarted the installer and the process began in earnest.

The first part of the processing sets up the installation (I reminded myself that the Mac had been backed up that morning -- just in case). After about 15 minutes the Mac began the restart. I always hate this bit. There was a slight delay while all applications were shut down in the user account, but when the computer restarted, the panel confirmed that the "Rescue" disk was being used. I started breathing again.

Tidying Up

I finished off by copying the latest Disk Warrior (Version 4.4) to the Applications folder on the disk. A new DVD arrived at my office this week, which I had ordered after the previous disk (a CD) had been damaged and became unreadable. To make sure, I ran Disk Warrior. When I entered my registration details, the installation was complete. I quit, shut down, removed the USB drive and put it in my back-pack.

I restarted the Mac, intending to get back to work, but instead of the Apple icon and the spinning gear wheel, a folder with a question mark appeared. I began to reach for my bag, but realised I had omitted to specify the startup disk. I turned the computer off and used the Option key startup to specify the correct partition. That did the trick and when the Mac was up and running again, I checked in System Preferences to make sure the right startup disk was highlighted.

Comments

I have also found this useful on the occasions that I want to run preventative maintenance on my Macs using Disk Warrior as the CD was slow (Alsoft confirm 5 - 15 minutes depending on the optical drive in the information sheet with my new DVD disk) and a disk like that is liable to damage: I have paid for two replacements in the last few years. Better to use the disk only when absolutely needed and rely on effective alternatives like an external, bootable drive. For the newer Macs that have no optical drives, this would also be another solution for maintenance and repairs.

As I found when the hard disk in my own iMac recently went into self-destruct mode, the use of the USB flash drive was able to run more tests that the OS X rescue installation, and to allow the saving of data which might otherwise have required more applications.

My extra hard disk is at my office right now waiting for the (overdue) return of the iMac with its new WD hard disk and once I have set that up with Mountain Lion and transferred the rescued data from the external disk, I will be updating OS X on that disk and also installing the latest version of Disk Warrior.

Graham K. Rogers teaches at the Faculty of Engineering, Mahidol University in Thailand. He wrote in the Bangkok Post, Database supplement on IT subjects. For the last seven years of Database he wrote a column on Apple and Macs.