For those with Seagate GoFlex external HD frustration -
I have seen several threads in here in the last year and a half about Seagate GoFlex external drives sleeping and becomming inaccessable. My drive is a Mac specific, Firewire 800 model (STBCxxxxxxx), and has been working flawlessly for 10 months (even with Seagate software installed). It suddenly developed the sleeping symptoms, but investigation has revealed another cause unrelated to either USB 3.0, non-Mac specific models (STACxxxxxxx), or Seagate drivers.
The symptoms were identical to what many others have described, the drive seemed to sleep and clicking on any of the destop partition icons produced the spinning ball of death. Or, attemps to shut down or restart resulted in a seeming hang up at a blank grey screen.
However, further investigation revealed that the drive was not actually asleep, despite it seeming to be so. By waiting when the spinning ball of death appeared, or when seemingly hung at a blank grey screen, eventually the action completed. That is, the hard drive desktop icon opened, or the blank grey screen disappeared and the computer shut down or restarted. However it was necessary to wait nearly 10 minutes in some cases.
I eventually discovered that Spotlight was attempting to index one or more of the external HD partitions when these symptoms appeared. Further investigation revealed that one of the partitions on the Seagate external had beome damaged or corrupt - even though it passed Disk Utility verifications. Spotlight continually tried to index this partition, and that was what was causing all the apparent sleeping like behavior.
Removing this partition returned the GoFlex to fully normal flawless behavior. So, if you are suffering GoFlex sleeping frustration, one other thing to check is clicking on Spotlight to see if it is indexing. It may be necessary to wait a minute or 2 while watching Spotlight to verify in an index operation is in progress.
If you see indexing and one or more partitions seem to constantly repeat indexing or take inordinately long to index, try adding that partition to the privacy ignore settings in System Preferences-->Spotlight. If that solves your problem then back up immediately and then erase the partition, possibly with the Security Setting to write one pass of zeros during the erase. This will identify and isolate any bad sectors on the magnetic media of that partition of the drive.