Recently, I have opened a ticket with Apple's bug reporter (item # 21477641) as I experience the same issue with my external LaCie drives (D2 Quadra, FW800). As my drives have been formatted with OSX' encryption option, the following may not be applicable to your particular situation but I encourage you to give this approach a try and report your findings. Try the following:
- Connect an external drive to your mac and format it with encryption enabled. Create 1..n partitions. One partition will suffice.
- Disconnect and reconnect the drive (just to be sure that it really has been ejected from the system
- Open bash and run diskutil list. My drive has three partitions where all of them have been unlocked. Output from diskutil looks like this:
/dev/disk3 (external, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *4.0 TB disk3
1: EFI EFI 209.7 MB disk3s1
2: Apple_CoreStorage AAAAA 2.6 TB disk3s2
3: Apple_Boot Boot OS X 134.2 MB disk3s3
4: Apple_CoreStorage BBBBB 1.1 TB disk3s4
5: Apple_Boot Boot OS X 134.2 MB disk3s5
6: Apple_CoreStorage CCCCC 279.2 GB disk3s6
7: Apple_Boot Boot OS X 134.2 MB disk3s7
/dev/disk4 (external, virtual):
#: TYPE NAME SIZE IDENTIFIER
0: Apple_HFS AAAAA +278.8 GB disk4
Logical Volume on disk3s6
40342379-A668-49B9-9F08-1DB51DD274CD
Unlocked Encrypted
/dev/disk5 (external, virtual):
#: TYPE NAME SIZE IDENTIFIER
0: Apple_HFS BBBBB +1.1 TB disk5
Logical Volume on disk3s4
4435349A-BF4F-4F66-AB54-47222DFC684F
Unlocked Encrypted
/dev/disk6 (external, virtual):
#: TYPE NAME SIZE IDENTIFIER
0: Apple_HFS CCCCCC +2.6 TB disk6
Logical Volume on disk3s2
DE421438-524E-4C12-9FFE-E8B354397E56
Unlocked Encrypted
Now eject all partitions via Finder. The drive will not spin down but it is continuously spinning. Run diskutil list again. It will tell you that all partitions have been ejected. Well, almost all of our partitions have been ejected.
/dev/disk3 (external, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *4.0 TB disk3
1: EFI EFI 209.7 MB disk3s1
2: Apple_CoreStorage AAAAA 2.6 TB disk3s2
3: Apple_Boot Boot OS X 134.2 MB disk3s3
4: Apple_CoreStorage BBBBB 1.1 TB disk3s4
5: Apple_Boot Boot OS X 134.2 MB disk3s5
6: Apple_CoreStorage CCCCC 279.2 GB disk3s6
7: Apple_Boot Boot OS X 134.2 MB disk3s7
/dev/disk4 (external, virtual):
#: TYPE NAME SIZE IDENTIFIER
0: Apple_HFS AAAAA +278.8 GB disk4
Logical Volume AAAAA on disk3s6
40342379-A668-49B9-9F08-1DB51DD274CD
Locked Encrypted
/dev/disk5 (external, virtual):
#: TYPE NAME SIZE IDENTIFIER
0: Apple_HFS BBBBB +1.1 TB disk5
Logical Volume BBBBB on disk3s4
4435349A-BF4F-4F66-AB54-47222DFC684F
Locked Encrypted
/dev/disk6 (external, virtual):
#: TYPE NAME SIZE IDENTIFIER
0: Apple_HFS CCCCC +2.6 TB disk6
Logical Volume CCCCC on disk3s2
DE421438-524E-4C12-9FFE-E8B354397E56
Locked Encrypted
Offline
Logical Volume AAAAA on disk3s2
40342379-A668-49B9-9F08-1DB51DD274CD
Locked Encrypted
Offline
Logical Volume BBBBB on disk3s6
4435349A-BF4F-4F66-AB54-47222DFC684F
Locked Encrypted
Offline
Logical Volume CCCCC on disk3s4
DE421438-524E-4C12-9FFE-E8B354397E56
Locked Encrypted
Now it's another time for diskutil. Run diskutil eject and eject any of the partitions between /dev/disk3s2 and /dev/disk3s7. As a result, your drive will spin down.
mac:~ jsl$ diskutil eject /dev/disk3s2
Disk /dev/disk3s2 ejected
mac:~ jsl$
(and yes, you can even eject the "Boot OS X" partitions - scary. That particular hard drive has no bootable partition installed btw).
Conclusion: There is a 'workaround' - at least for encrypted external drives. Your miles may vary for non-encrypted external.
Side notes:
- The issue has not been fixed with the latest El Capitan beta. Note that prior to El Capitan, there was a "GUI workaround":
- enable debug mode for Disk Utility
- enable 'show all drives' option
- Once all encrypted partitions have been ejected via Finder, eject the "Boot OS X partition" via Disk Utility.
- As Apple has seriously tampered with Disk Utility's advanced functions, that GUI feature is now gone and you need to use the command line approach.
- The issue did not occur with Snow Leopard - my old MBP is happy to trigger 'spindown' ejects whenever I eject the drives.
- My MacMini and newer MPB are both running Yosemite and El Capitan - both machines show the same symptoms.
Last but not least: this approach will not help you with the energy saver spindown issue as the drive keeps spinning and spinning and spinning .... So far, I have found no workaround for that issue.
The bug reporter ticket is still pending review.
Hope this helps!