external-diskfile-sharingmacosNetworkusb
I have an iMac with an external USB 1TB harddrive, running Mountain Lion. Under File Sharing I have added this external drive to my list of "Shared Folders".
I have a MacBook Pro also running Mountain Lion and I want to be able to access the external drive on the iMac, but it's not showing that drive when I access the iMac via Finder on the MacBook Pro.
What am I doing wrong?
If your USB hard drive is the bus-powered variety (that is, you don't plug it into the wall for power), then it is possible that it is requiring too much startup current to run on one of your computers.
Some computers are pickier than others about how much current a device can draw, and over what period.
You might try a cable like this:
Basically, you can use power from two USB ports, instead of just one.
If your hard drive has a jack for a power adapter, use that instead.
It should be as simple as:
Step Zero: Make sure you have a verified, complete, bootable backup of your Snow Leopard setup, "just in case". (And make sure that drive isn't attached when you are installing Mountain Lion, so you don't accidentally choose it.)
Attach external drive to MacBook Pro. Format as "Mac OS Extended (journaled)". Give it a clear and distinct name such as "EXTERNAL DRIVE FOR LION"
Launch App Store.app. Purchase Mountain Lion.
Wait wile the installer downloads. It's ~4gb, so you'll be waiting awhile.
When the installer finishes downloading, it will automatically launch and prompt you to start the upgrade process. DON'T PANIC. Nothing will be done until you tell it to proceed.
(OPTIONAL BUT HIGHLY RECOMMENDED STEP) Before you start the installation process, quit the installer. Then, go to Finder and open the /Applications/ folder and look for an app called something like "Install OS X Mountain Lion.app". Drag it from /Applications/ to somewhere else, like your Desktop. (You may be prompted to enter your password to do this. That's OK.) Why do this? Because if you leave the installer in /Applications/, it will be automatically deleted when the installation completes. I recommend keeping it around because it is useful if you want to make a USB installer or something like that. Once you have moved it, launch the "Install OS X Mountain Lion.app" again.
Very early on in the process you should be able to choose which drive you want to install Mountain Lion to. (You may have to click on a 'Customize' button in the installer.)
Choose the "EXTERNAL DRIVE FOR LION" drive and follow the rest of the prompts in the OS X installer.
After the installation starts, it will reboot your computer from the external drive and continue the installation. Make sure this is not interrupted.
When it is done, you can choose the default Startup Disk in System Preferences, or hold down the Option/Alt key when the Mac is booting up.
Bonus Tip: QuickBoot is a free app which will let you reboot your Mac using a different drive than the default startup disk without changing the default startup disk.
Just go slow, watch what you are doing, and it should be very straight-forward.
(Nevertheless, don't forget Step Zero. Have you booted from your backup drive lately to make sure it really boots?)
Best Answer
I've realised that all the time the external drive is NTFS file system, it won't share it, but as soon as I formatted it to Mac OS Journalled FS, it appeared straight away.