I did respond
, but maybe in a too-verbose manner*.
Here's what you have now:
A drive with the Yosemite installer
on it. You could use this to install Yosemite. I thought I remembered that you'd need to copy it to the Mac's Applications folder and run it from there, but I guess I'm wrong about that.
Here's what you want:
A bootable volume on the hard drive.
You have three choices here, and all three can live independently on the drive, but each will need its own partition, I think.
1. Install Yosemite on a partition. You might have to run the installer from a different partition, but maybe not.
You could install Yosemite on the same partition that has the Yosemite Installer. The Macworld article I referenced above will tell you how big this partition needs to be. Or you can look up that info.
2. Build a bootable partition on the drive with DiskWarrior Recovery Maker.app. This will copy the OS X recovery volume on your Mac to the partition on your external drive and copy DiskWarrior to the same partition. This partition must be 2 GB or larger.
You boot from this partition by plugging in the drive and powering it up, then using option during a restart or using System Preferences > Startup Disk.
You will boot into the OS X recovery environment resident on the external
drive. DiskWarrior will be a choice in the main menu.
3. Clone the original DiskWarrior flash drive to a partition on your drive. (I'm guessing this will work.)
This partition should work just like the original flash drive. It boots earlier Macs. To boot a recent Mac, you first boot the Mac into its own on-board
OS X recovery environment. Then you use Terminal to start DiskWarrior. Type /Volumes/DW/go in Terminal.
1 or 2 may work even if the target Mac's internal drive has no recovery volume. 3 requires a functional recovery volume on the target Mac.
If the target Mac's hard drive is really hosed, it could prevent startup even from an external drive because the OS stalls seeing if it can mount the internal drive.
* You know what they say about science-trained science writers? Ask them the time and they tell you how to build a watch.