Difference between Bootable USB OS X thumb drive and Recovery USB thumb drive

[iMikeT]

I'm getting around to finally upgrading to 10.8 Mountain Lion from 10.7 Lion and I want to clean install OS X.

I have a 27" 2011 iMac with a 1TB HDD that I partitioned into 4 drives and it's been filling up with garbage that I'd like to completely clean up and start with a blank internal drive. I'll probably repartition the drive anyway but I'd like to do all of the Disk Utility tasks while running OS X externally.

With that, I know that I need a bootable/recovery drive. So what's the difference between the two? Obviously, I know that I can boot OS X from a bootable drive but what about the recovery drive?

After getting this external drive up and running, how will I be able to install OS X onto the internal drive of my iMac from my external drive?

 

[Weaselboy]

A recovery drive is just a drive that contains the 650MB recovery HD from Lion or Mountain Lion. So once you have Lion or ML installed, you use this utility from Apple along with a 1GB USB key (or you could use a 1GB external drive partition) to make the recovery drive. So if your disk drive dies, you can put in a new drive and boot from the recovery key to format and reinstall the OS.

With your 2011 iMac, there really is no need to have this recovery drive as the firmware has a method to access this built in. So if you have a dead internal drive, just command-r boot and the firmware will see there is no readable drive and it will DL a 650MB recovery image over the Internet... getting you to the same recovery tools you would have if you booted from the recovery USB key.

This is all different than having a full installer on a USB key or external drive. To do that you need to DL the full installer from the App Store, then use either Disk Utility or an app like this to make yourself a 8GB USB key (or external 8GB partition) full installer. By booting to this installer you can reinstall the entire OS without having to DL anything again from the Internet.

So to clean install from Lion to ML in your case, I would make the full ML installer while still in Lion. Then option key boot to the installer key (or drive) and use Disk Util to erase Macintosh HD, then proceed with the ML install. This will give you a clean install of ML.

 

[iMikeT]

A recovery drive is just a drive that contains the 650MB recovery HD from Lion or Mountain Lion. So once you have Lion or ML installed, you use this utility from Apple along with a 1GB USB key (or you could use a 1GB external drive partition) to make the recovery drive. So if your disk drive dies, you can put in a new drive and boot from the recovery key to format and reinstall the OS.

With your 2011 iMac, there really is no need to have this recovery drive as the firmware has a method to access this built in. So if you have a dead internal drive, just command-r boot and the firmware will see there is no readable drive and it will DL a 650MB recovery image over the Internet... getting you to the same recovery tools you would have if you booted from the recovery USB key.

This is all different than having a full installer on a USB key or external drive. To do that you need to DL the full installer from the App Store, then use either Disk Utility or an app like this to make yourself a 8GB USB key (or external 8GB partition) full installer. By booting to this installer you can reinstall the entire OS without having to DL anything again from the Internet.

So to clean install from Lion to ML in your case, I would make the full ML installer while still in Lion. Then option key boot to the installer key (or drive) and use Disk Util to erase Macintosh HD, then proceed with the ML install. This will give you a clean install of ML.

Thanks for the feedback. This definitely helped clarify some questions and misconceptions that I had.

I was always under the impression that it was only notebook Macs that had the recovery partition built-in. If that's the case, is the recovery partition something that was installed onto the logic board after I upgraded to 10.7 Lion? (I bought my 2011 iMac after the Lion release date was announced and it shipped with 10.6.8 Snow Leopard and I was given a voucher for Lion)

I think what I'll do is install 10.8 Mountain Lion to an external drive to begin with while still in 10.7 Lion. Then boot my iMac off the external drive, use Disk Utility to format the iMac's internal drive, then clean install Mountain Lion onto the iMac while running OS X off the external drive. Whew....

 

[Weaselboy]

Thanks for the feedback. This definitely helped clarify some questions and misconceptions that I had.

I was always under the impression that it was only notebook Macs that had the recovery partition built-in. If that's the case, is the recovery partition something that was installed onto the logic board after I upgraded to 10.7 Lion? (I bought my 2011 iMac after the Lion release date was announced and it shipped with 10.6.8 Snow Leopard and I was given a voucher for Lion)

I think what I'll do is install 10.8 Mountain Lion to an external drive to begin with while still in 10.7 Lion. Then boot my iMac off the external drive, use Disk Utility to format the iMac's internal drive, then clean install Mountain Lion onto the iMac while running OS X off the external drive. Whew....

Two different things. Any Mac with lion or mountain lion installed gets a Recovery hd partition installed on the drive as part of the installation.

In addition to this 2010+ portables and new iMacs have Internet recovery built into the firmware. So even if the drive dies, you can boot to recovery from firmware and download the OS and reinstall. For newer machines that did not come with this capability, it was added with a firmware update after Lion came out.