Note: This situation is evolving. Please see the output at the end of this question for the current situation.I'm using Linux Mint 14. Recently, I repartitioned one of my hard drives, and I backed up all my data to an external USB 500GB drive. Now I am trying to copy that data back.However, the drive is behaving strangely. When I plug it in, it shows up on my desktop:... but when I right click and select to view Properties, underneath the Permissions tab, it says:The permissions of USB500 could not be determined.Also, it shows that 359.7 GB of the drive is used, which is about the right amount for the data I backed up:... but, when look into the drive, most of the files are not visible to me. For example, when I look at the properties of the dave directory, where most of my files are backed up, it says it's only 1.3 MB in size:There should be more like 300GB in that folder.Why are most of my files seemingly missing when the data used on disk is so much larger? Why is the permissions not determined?Most importantly, what is the safest process for me to diagnose problems and retrieve the data off this disk?Update: This output was requested in an answer below:$ mount | grep USB500/dev/sdd1 on /media/dave/USB500 type ext4 (rw,nosuid,nodev,uhelper=udisks2)When I ran the following command, I got a huge stream of lines that ended with Input/output error (too many to reproduce here, but they're all basically the same):$ sudo find /media/dave/USB500 -ls | lessfind: `/media/dave/USB500/dave/.guayadeque': Input/output errorfind: `/media/dave/USB500/dave/.compiz-1': Input/output errorfind: `/media/dave/USB500/dave/.anthy': Input/output errorfind: `/media/dave/USB500/dave/.compiz': Input/output errorfind: `/media/dave/USB500/dave/Apache_Logs': Input/output errorfind: `/media/dave/USB500/dave/.avidemux': Input/output errorfind: `/media/dave/USB500/dave/.dvdrip': Input/output errorOn the one hand, this seems to indicate a possible hardware failure(?). On the other hand, it is listing all the files I'm hoping to recover... so is it possible they are accessible? I really hope so...Update 2: I tried running fsck in hopes of repairing the drive and recovering at least some data, but I got this response:$ sudo fsck -y /dev/sdbfsck from util-linux 2.20.1e2fsck 1.42.5 (29-Jul-2012)fsck.ext2: Attempt to read block from filesystem resulted in short read while trying to open /dev/sdbCould this be a zero-length partition?Sometimes the drive does not seem to mount, I have not determined a pattern as to what causes it to become un-mountable. After turning it off and on, or after a reboot, I seem to be able to get it back.I removed the hard drive from it's USB interface and connected it to the computer's internal P/SATA bus, but it seemed that the drive behaved exactly the same, with identical symptoms.I believe this drive is dying, so right now the goal is to try to find some way to access the data that should be there just long enough to copy as much of it as possible. Suggestions on how I might do that would be most appreciated. There are actually just a few key directories I would like to access, so hopefully, if the failure is not too global, I might be able to get what I need.Update 3: I'm currently running the following command. I started it a day ago, and it's still going. I hope it is doing something useful. If anyone can confirm for me what the output below indicates about its progress, that would be very helpful.$ sudo ddrescue -r3 /dev/sdb /home/dave/RECOVERY/usb500.image/home/dave/recovery_usb500.logfilePress Ctrl-C to interruptInitial status (read from logfile)rescued:         0 B,  errsize:       0 B,  errors:       0Current statusrescued:         0 B,  errsize:    500 GB,  current rate:        0 B/s   ipos:     5366 MB,   errors:       1,    average rate:        0 B/s   opos:     5366 MB,     time from last successful read:       1 dSplitting failed blocks...
USB 500GB external drive mounted with undetermined permissions, missing data
permissions;usb;hard disk;data recovery;external hdd