Time Machine corrupting external USB hard drives
In February I installed two Mac Minis running 10.8 Server. Each machine had an external hard drive connected to it.
Sometime over the Labor Day weekend, both drives stopped working. When I came in Tuesday, each machine had a message on the screen that the Time Machine drive had been improperly ejected. I powered down both drives and then powered them back up. Here's what is going on with each machine:
MACHINE #1:
Has a Western Digital 1TB drive formatted as OS X Extended Journaled.
Disk Utility is able to see the external drive; however, whenever I try to back up, I get the message "Time Machine couldn't complete the backup... Files can't be copied onto the backup disk because it appears to be read-only."
In Disk Utility, if I select the partition and Verify Disk, I get the message "Disk Utility stopped verifying Backup. Couldn't unmount disk."
When I try to reformat the drive, I get the message "Disk Erase failed. Disk Erase failed with the error: Couldn't unmount disk."
The Time Machine System Preference pane shows "None" for both oldest and latest backup times; however, I am able to enter Time Machine and see files going back to April.
MACHINE #2
Has a Segate 2TB drive formatted as OX X Extended Journaled.
Initially Disk Utility would recognize this drive about 50% of the time. I would power it down and back up. Sometimes it would appear in Disk Utility, sometimes it wouldn't. Whenever I would try to verify or repair this disk, it would immediately unmount and I would get the message that the disk was not ejected properly. When I try to backup using Time Machine, TM acts like it is preparing to back up and then the disk disappears from Disk Utility and from the Desktop and I get the message that The disk was not ejected properly.
This machine showed it was last backed up on September 1.
After fiddling with it, I was able to format the drive. After formatting the drive, I started a Time Machine backup and the drive unmounted again.
It seems that some event over the weekend caused both drives to corrupt. There was no sign of a power-outtage. Can anyone suggest how I can track down what caused this? Would there have been a maintenance script that would have run on Sept 1 that could have messed both drives up? Some other system event? Losing the data isn't a big deal. I just want to make sure I prevent whatever caused this in the future. Any tips would be much appreciated.
Time Machine-OTHER, OS X Mountain Lion (10.8.4)
