I have an external USB drive that I have plugged into a USB hub, which gets unplugged from my computer about once a day. Most of the time I remember to unmount the drive before disconnecting so that I don't break anything. Sometimes I forget and get the message about "usb drive disconnected unexpectedly" (or something similar).
About the drive: it is a 1TB usb-powered Western Digital drive that I use for Time Machine and other misc. documents. The drive is encrypted with FileVault2, which I think was done automatically when I told Time Machine to use it (my system drive uses FileVault2).
About the OS: OS X Mountain Lion 10.8.2 (can't say issues started w/ any recent updates, but does seem to fall somewhere within install time periods of 10.8, 10.8.1 and 10.8.2 installs)
Recently, this drive has not been showing up every time I connect the USB hub. Yesterday I noticed that the last Time Machine backup was a few days prior. Last night I waited to plug it in until my computer was out of sleep, and this time I switched to a different port on the USB hub. The drive mounted without an issue.
Today, I went to unmount the drive (via right-click on desktop), and got a message: "My Passwort" is a partition on a disk that has 2 partitions. Do you want to eject "My Passport" only, or both partitions? ....
When I go to OS X Disk Utility, there is only one partition showing under the drive.
Q1: any ideas why the drive not showing up every time I connect over the last few months (sometimes it does, other times it didn't)?
Q2: why does the OS think there are two partitions?
Update 2: Ran diskutil list, got following result:
/dev/disk0
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *128.0 GB disk0
1: EFI 209.7 MB disk0s1
2: Apple_CoreStorage 127.2 GB disk0s2
3: Apple_Boot Recovery HD 650.0 MB disk0s3
/dev/disk1
#: TYPE NAME SIZE IDENTIFIER
0: Apple_HFS disk0s2 *126.9 GB disk1
/dev/disk2
#: TYPE NAME SIZE IDENTIFIER
0: FDisk_partition_scheme *32.0 GB disk2
1: Apple_HFS mini32gb 32.0 GB disk2s1
/dev/disk3
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *1.0 TB disk3
1: EFI 209.7 MB disk3s1
2: Apple_CoreStorage 999.8 GB disk3s2
3: Apple_Boot Boot OS X 134.2 MB disk3s3
/dev/disk4
#: TYPE NAME SIZE IDENTIFIER
0: Apple_HFSX My Passport *999.5 GB disk4
Update 3: As noted in my comment below, I think Mountain Lion may have installed a recovery partition on my external drive, perhaps as a secondary safety measure in case my primary drive completely dies. If this is the case, it wasn't preferred by me, so I guess take-home lesson is if you want to avoid this, unplug your externals before upgrading.
Final Update: I was tired of this message showing up, so I removed the partition with the following command (repeated for the EFI and the boot partition on my external):
diskutil eraseVolume "Free Space" Blank <DISK_NAME> # WARNING: CAREFUL WHICH VOLUME YOU ERASE!!
