external-diskhard drivemacbook promountusb
I have a USB external hard drive with AC adapter that works fine with an Ubuntu machine. But when I plug it into my MacBook Air it lists one partition on the finder, and does not mount the other.
Even though it is listed on the finder, it shows that there are no files on the drive (even though there are).
Tried both USB ports with the same result.
Disk Utility does not see it.
How to fix?
OSX 10.7.5
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.
This seems like an issue with the chosen file system.
What file system did you choose when formatting the hard drive? If it's not HFS(+), FAT in any fashion or NTFS you cannot read it on OS X without additional software. If it's Ext, you could go with Paragon's Ext for Mac (but it costs some bucks).
In future, best choose exFAT when formatting an external hard drive if you need to use it on different operating systems. It both allows rather large files (which is heavily limited in FAT32), but can be both read and written in all important operating systems.
Best Answer
The answer to your questions is in the "Disk Utilities" application: just type this in the search box on the top-right corner of your screen, and launch the application.
For every device connected, you will see much information. Relevant to analyse your problem is the "format" information: HDFS, Mac OS Extended, ExFAT, FAT32, ext3, ext4...
I guess because your harddisk comes from Ubuntu, it must be ext3 or ext4. If that is the case, please read the following answer for further help: https://apple.stackexchange.com/a/29914/44080