Stalled or very slow shutdown if external drive is attached
Summary
As of a few days ago, my iMac consistently takes a long time to shutdown. In a few tries, the time range I've seen is from 3 minutes to more than 57 minutes (then I gave up and held the power button down). While stalled, the display is black with an active mouse pointer (moving the mouse moves the pointer).
This only occurs when my external drive is attached. Without it, the iMac shuts down quickly, not showing the black-screen-with-pointer at all.
Do you think there's something wrong with this external drive? I cannot reformat it without buying another big drive.
Thanks,
Wallace
Further details
This is happening immediately after a wipe of the internal drive (set the partition to Apple and then to GUID to really wipe it) by the Apple Store, to try to fix a startup problem wherein the iMac either
(1) showed a circle with slash on a gray screen (no boot disk) and automatically shut down again, or
(2) showed the flashing globe on black (network boot?) for a while before booting up normally. Total boot time till I could log in was 1m15s--very slow.
Curiously, case (1) happened only if this external drive was connected. The wipe has eliminated these symptoms.
And that problem came up days after getting the iMac back from the Apple Store after investigation of a weird one-time video problem. During boot, the display showed about four rolling horizontal bands (like Venetian blinds) going up the screen, replacing the whole regular screen with black within 15 seconds or so and then bringing the regular screen back again. This happened during startup and continued after log-in, until the iMac froze. The Apple Store said they hadn't heard of such a problem, and indeed I couldn't find anything like it on the web. They kept it for a few days for diagnostics and stress tests and found nothing wrong, and it has not recurred. Pretty worrisome, though, for the future reliability of this expensive machine. Here's a picture while the bands were rolling up, re-exposing the green rice-paddy desktop:
When I run Disk Utility to verify or repair this external disk, I get the following alert about lacking an EFI system partition. I use this external disk only to store extra files that won't fit on the internal drive, so I don't think this is a problem.
EtreCheck report:
Problem description:
After a 57-minute hang on restart, during shutdown, I manually powered down (held power button) and then turned on again.
EtreCheck version: 2.3 (135)
Report generated 8/2/15, 7:59 PM
Download EtreCheck from http://etresoft.com/etrecheck
Click the [Click for support] links for help with non-Apple products.
Click the [Click for details] links for more information about that line.
Hardware Information: (What does this mean?)
iMac (Retina 5K, 27-inch, Late 2014) (Technical Specifications)
iMac - model: iMac15,1
1 3.5 GHz Intel Core i5 CPU: 4-core
8 GB RAM Upgradeable
BANK 0/DIMM0
4 GB DDR3 1600 MHz ok
BANK 1/DIMM0
4 GB DDR3 1600 MHz ok
BANK 0/DIMM1
Empty
BANK 1/DIMM1
Empty
Bluetooth: Good - Handoff/Airdrop2 supported
Wireless: en1: 802.11 a/b/g/n/ac
Video Information: (What does this mean?)
AMD Radeon R9 M290X - VRAM: 2048 MB
iMac 5120 x 2880
System Software: (What does this mean?)
OS X 10.10.4 (14E46) - Time since boot: less than an hour
Disk Information: (What does this mean?)
APPLE SSD SM0256F disk0 : (251 GB) (Solid State - TRIM: Yes)
EFI (disk0s1) <not mounted> : 210 MB
Macintosh HD (disk0s2) / : 250.14 GB (121.13 GB free)
Recovery HD (disk0s3) <not mounted> [Recovery]: 650 MB
USB Information: (What does this mean?)
Seagate Backup+ Desk 4 TB
Whi4TB (disk1s1) /Volumes/Whi4TB : 4.00 TB (1.21 TB free)
Recovery HD (disk1s2) <not mounted> [Recovery]: 650 MB
Apple Inc. BRCM20702 Hub
Apple Inc. Bluetooth USB Host Controller
Apple Inc. FaceTime HD Camera (Built-in)
Thunderbolt Information: (What does this mean?)
Apple Inc. thunderbolt_bus
Gatekeeper: (What does this mean?)
Mac App Store and identified developers
Launch Agents: (What does this mean?)
[not loaded] com.adobe.AAM.Updater-1.0.plist [Click for support]
[loaded] com.adobe.AdobeCreativeCloud.plist [Click for support]
Launch Daemons: (What does this mean?)
[running] com.adobe.adobeupdatedaemon.plist [Click for support]
User Launch Agents: (What does this mean?)
[not loaded] com.adobe.AAM.Updater-1.0.plist [Click for support]
User Login Items: (What does this mean?)
iTunesHelper Application (/Applications/iTunes.app/Contents/MacOS/iTunesHelper.app)
Internet Plug-ins: (What does this mean?)
Default Browser: Version: 600 - SDK 10.10
AdobeAAMDetect: Version: 3.0.0.0 - SDK 10.9 [Click for support]
QuickTime Plugin: Version: 7.7.3
Safari Extensions: (What does this mean?)
AdBlock
3rd Party Preference Panes: (What does this mean?)
None
Time Machine: (What does this mean?)
Time Machine not configured!
Top Processes by CPU: (What does this mean?)
3% fontd
2% WindowServer
0% taskgated
0% cloudpaird
Top Processes by Memory: (What does this mean?)
668 MB kernel_task
188 MB loginwindow
123 MB Dock
115 MB mds_stores
90 MB Finder
Virtual Memory Information: (What does this mean?)
5.20 GB Free RAM
2.80 GB Used RAM (1.12 GB Cached)
0 B Swap Used
Diagnostics Information: (What does this mean?)
Aug 2, 2015, 07:50:39 PM Self test - passed
Aug 2, 2015, 06:39:16 PM ~/Library/Logs/DiagnosticReports/Creative Cloud_2015-08-02-183916_[redacted].crash
Aug 2, 2015, 04:39:27 PM ~/Library/Logs/DiagnosticReports/Install_2015-08-02-163927_[redacted].crash
Aug 2, 2015, 03:09:06 PM ~/Library/Logs/DiagnosticReports/nsurlsessiond_2015-08-02-150906_[redacted].cra sh
I'm getting an error when I try to post this ("The message contains invalid characters"), so I will cut this off here and later will post the Console logs.
iMac (Retina 5K, 27-inch, Late 2014), OS X Yosemite (10.10.4)
