By Graham K. Rogers

Despite a new 4 TB Western Digital disk in exchange for the LaCie 2TB disk, there were still signs of problems when I began to test the new one. There should have been no problem with the LaCie disk, but somehow it was reporting spontaneous disconnections as if power was failing or the cable connection to the computer had failed.

With the Western Digital disk, I initially tried to cause such a disconnect by moving the cable in the Thunderbolt ports on the Mac (I tried both). The cable itself was a new one: bought when the LaCie disk was purchased. The connection remained firm.

The Western Digital My Book Thunderbolt Duo arrived formatted for the Mac and with a Striped RAID (RAID 0) setup. I added it to the list of Time Machine disks and the first backup (around 250 TB) was completed fairly quickly. I had earlier checked data transfer speeds on the other disks:

• 500 GB Imation with USB 2.0 - 36.43 seconds

• 1 TB Imation disk with Micro-B USB 3.0 - 17.28 seconds.

• 500 GB LaCie Big Disk with Firewire 800 and Thunderbolt adapter - 23.86 secs

• 2 TB Western Digital My Book Studio disk with Firewire and the adapter - 24.53 seconds

• 2 TB LaCie Little Big Disk with Thunderbolt - 9.61 seconds

Transferring the same file to the new WD disk took 06:93 seconds. I was suitably satisfied for the moment.

Later the Finder reported that the disk had not been ejected properly. Fortunately there was no damage either to disk or data, but I looked further. The common points with both disks was that Time Machine was being used; that the disks were used in striped RAID configuration; that I was away from the computer on most occasions that this was reported; and both disks had used the same Thunderbolt cable.

I removed a couple of factors from that list by reformatting the disk as two separate 2 TB disks; and by removing it from the Time Machine backup list. Reformatting had erased the data of course, so that was an easy decision, at least as a way to try and find out the cause. I did initially try one of the disks with Time Machine, but the initial backup took so long (considerably slower) that I abandoned that path.

With the disk (or disks) just connected and no data transfers taking place, I left the computer running and left the room. When I returned an hour or so later, the Finder reported that the disk had not been ejected properly.

This removed two ideas from the list (Time Machine and RAID) but added one more. I wondered if Energy Saver preferences, including Power Nap and Put hard disks to sleep were affecting this in any way.

I wrote a note to Topher Kessler asking him for help. He has recently set up the MacIssues site after CNet shuttered MacFixit and had just written on hard disk issues. He was quick to reply and asked some questions in confirmation. In one email he asked about the Thunderbolt cable. He made the point that the cables are active and have electronics in their terminals. They could be interrupting the data connection if they were malfunctioning.

As I was in Siam Discovery Center when I received that email, I went directly into the iStudio store and this time bought a 2m Thunderbolt cable. I had originally made do with the 0.5m version.

Further Analysis

I came back a while later to find a warning message about one of the two disks. When I moved the icons over the Eject button, I was warned that one was ejected wrongly, but that the other "could not be ejected because Calendar and other applications are using it. When I did manage to eject it, I swapped the cables and ports, then reformatted the disks again, renaming them in the process. I also used a different power port (mains electricity), just to try all possibilities. That seemed to work. After something over 2 hours, I came back to the Mac to find that there was no message regarding a spontaneous ejection.

Over the next 24 hours, when the disks were connected, there were no reports of any further spontaneous ejections. In the meantime, the Time Machine backup disks (Firewire and USB 3) appeared on the desktop as normal and the backups were fine.

As the problem had seemed to have gone, I decided to take things a little further and created a striped RAID set by dragging the partitions on each disk into the panel in the RAID section of Disk Utility. To tempt fate a little more, I replaced the bland orange disk icon with an icon from a set of Andy Warhol icons I had downloaded years ago.

Overnight I kept the Mac running and the disk attached. There was no ejection reported by the Finder. In the morning, I added the disk to the list of Time Machine backups and waited for the process to begin. With a reported 289.22 GB of data to backup initially. This took longer than I had expected at around 1 hour 20 minutes. So far, there has been no repeat of the ejection problem that has so plagued my use of these disks connected using Thunderbolt cables.

Tentative Solutions

The inclusion of "Power Nap" in the newer computers, removes the need for the slider controlling Computer Sleep, but may introduce other variations in the way that certain internal and external hardware operates with OS X and the computer.

To try and prove this, I first backed up the computer one more time using the FW 800 My Book Studio that has been the main Time Machine disk for the last few months (I had earlier also completed Time Machine backups at work with the USB 3-connected 1 TB Imation disk). I removed the FW 800 disk and connected the My Book Thunderbolt Duo disk and backed up one more time.

Aware of the potential for more damage, with the disk still connected, I checked the box beside, "Enable Power Nap while plugged into a power adapter". Note also that below this, Apple has a comment that While sleeping, your Mac can back up using Time Machine and periodically check for new email, calendar, and other iCloud updates.

There was no spontaneous rejection. I then checked the box, "Put hard disks to sleep when possible," but again, after several hours, there was no report that the disks had tried to eject themselves. I then deselected Prevent computer from sleeping automatically when the display is off" and again, the connection was stable. To tempt providence, I disconnected the power supply from the Mac.

All was fine, but when the disks were connected later, there was a further ejection. I re-checked the box, Prevent computer from sleeping. . . " and tried again: no success. I then unchecked the box, "Put hard disks to sleep when possible" - this time, the disk did not eject.

When the stability began to return, I speculated that when OS X senses no need to maintain power at normal levels - for example when the system is semi-dormant - the power is allowed to drop. This may suit the Mac itself with its better management systems and lower power draw with the new Haswell processor, but the Thunderbolt cables need power to be maintained. I do not think that it is a problem with the Western Digital disk, as the LaCie disk also exhibited the same behaviour.

The disks no longer eject spontaneously (at least for now). What brought back the stability that I should have had from the beginning, is unclear, I must be honest. I think I have a handle on it now. Perhaps a combination of cable change, changing the System Preferences > Energy Saver (plus a restart or two in between) had done the trick.

I am still wary about trusting data to the new Thunderbolt disk, at least when it is not monitored. If I complete any necessary backing up then eject the disk, that should be fine, but it is a far cry from the plug and play and leave it that I was expecting.

In the meantime, I have submitted feedback to Apple.

See Also:

• Comparing LaCie Little Big Disk Thunderbolt Speeds with Other Disks and Connectors

• Western Digital Releases 2TB and 4 TB Thunderbolt Disks

• Backing up on a Mac - External Hard Disks, Bangkok Post, Life

• Breaking-in a New LaCie Little Big Disk: Oops (My mistake) - Recovery

• Breaking a New LaCie Little Big Disk: Oops Again - Not My Mistake

Graham K. Rogers teaches at the Faculty of Engineering, Mahidol University in Thailand where he is also Assistant Dean. He wrote in the Bangkok Post, Database supplement on IT subjects. For the last seven years of Database he wrote a column on Apple and Macs. He is now continuing that in the Bangkok Post supplement, Life.