Disk Utility repair option doesn't repair anything. Thanks, I will check it out.
In the meantime...
By the way, may be it is silly, but I wrote this in Apple forums and another person had the same response.
I had disable spotlight in one of my 3 partitions. That's the one that is still working, the other 2 are the ones that unmount in my WD My Passport 1Tb hard drive.
May be spotlight is part of the problem?
Another person reply:
I had two drives connected to my iMac i5.
1.) FreeAgent Desk Seagate Drive 1TB was connected through FireWire. ( the affected drive )
2.) WD MyBook Drive 3TB was connected through USB. ( not affected )
INTERESTING part is... The WD Drive was already added to the Spotlight Privacy to " Prevented Spotlight from searching these locations" BEFORE i installed Mavericks.
The affected Drive had certain folders in the Privacy and those specific Folders were NOT affetcted but all other files on that Drive were. hmmmm... And all the files affected were between 11:50am and 2:00pm. I will see if i can find out if there is a log file of when Spotlight Indexes. I know I've caught Sportlight Indexing more than it should latelly too.
So MAYBE this IS a Spotlight issue??
I know there are people in this forum that the problem keeps happening repeatedly, maybe they can TEST out this theory and add that drive to the "Spotlight Privacy" and see if that eliminates the problem.