updated 09:45 pm EDT, Mon July 16, 2012
Problem isolated to inexpensive bridgeboards, chipsets
Almost immediately after USB 3.0-equipped Macs were announced by Tim Cook at the 2012 Worldwide Developers Conference, MacNN started receiving tips that there were sporadic problems involving USB 3.0 external drives not mounting properly. The reports were scattershot, with reports of one drive working fine on one machine, but not on the Retina MacBook pro, or alternatively, working on the 2012 MacBook Pros but not the just-refreshed MacBook Air. To get to the bottom of the problem, we contacted an independent lab to set up tests of various combinations of new MacBooks and USB 3.0 drives to look into the phenomenons and, hopefully, find a root cause.
The MacNN-contracted labs tested two Retina display MacBook Pros with production dates three weeks apart, a 2012 11-inch MacBook Air, a LaCie USB 3.0 PCI Express card, and a Sonnet Echo Express Thunderbolt PCI-E expansion chassis. A 2TB Western Digital Caviar Green hard drive was swapped into 33 different USB 3.0 cases for testing. Each mounting test and large data copy was performed twice with USB 3.0 cables from different manufacturers to eliminate cabling as a factor. A Beagle USB 5000 SuperSpeed protocol analyzer was used for amplifying details.
The older of the two 2012 MacBook Pros failed to properly mount the CoolDrives USB3-Alum-35 single drive case and the Mediasonic Raid+ HUR1-SU3S2 2-bay hard drive enclosure. The Mediasonic single drive HD6-SU3-BK and the Rosewill RX-35-AT-SU3 single drive case would mount, but wouldn't stay mounted reliably. The three-week newer MacBook Pro also wouldn't mount the Mediasonic RAID case, and had intermittent problems with the Mediasonic single-drive and Rosewill single-drive case during large file copies. Every case from LaCie and Other World Computing that was tested worked fine in every regard.
When using USB 2.0 cabling -- forcing the drive enclosures to negotiate at the lower speed -- there were no problems with any case, in any configuration, on any computer. All of the cases mounted, and stayed mounted, even after a 100GB large file copy test.
Interestingly, none of the enclosures had any problem mounting and staying mounted on either the MacBook Air or on either Retina MacBook Pro through a Thunderbolt connection to the the Echo Express chassis with LaCie USB 3.0 card. This suggested some sort of incompatibility between the Apple Retina MacBook Pro implementation that did not exist on the new MacBook Air.
The MacBook Air was not without its own problems, however. A Verbatim 32GB USB 3.0 Store and Go flash drive was unreliable, and would mount but not stay mounted. While the MacBook Air provides sufficient power in regards to the USB 3.0 spec, it appears that sometimes some flash drives demand just a bit more power than the MacBook Air supplies, and the drive unmounts.
The troublesome Mediasonic and CoolDrives hard drive cases were then connected to the Beagle USB 5000 analyzer. For those not familiar with the analyzer, it stands between the host computer and the USB client drive, and unobtrusively intercepts and records the data for analysis. After five power-on cycles on both the cases and MacBook Pro, the data was compiled and analyzed. For comparison's sake, two LaCie cases were also tested with the Beagle USB 5000 device, using the same five data collection cycles.
With both troublesome USB 3.0 cases, the Retina MacBook Pro would send the high-speed test "ping" and would wait for an acknowledgement of higher speed capability that wouldn't arrive in the timing window, or on occasion, wasn't recognized as an acknowledgement of the higher speed. For reasons that our lab was unable to determine, the USB 2.0 speed synchronization would occur in a similar fashion, with the timing being off, preventing proper reception by the Retina MacBook Pro. The Mediasonic case was sent back to the manufacturer, and the replacement acted in the same fashion, suggesting a firmware update on the Retina MacBook Pro could rectify the problem by loosening the timing of the acknowledgments. The LaCie cases reported within the speed negotiation window 100 percent of the time, and would connect and mount at full USB 3.0 speed with no problems.
The problem is reminiscent of early OS X teething problems with inexpensive FireWire chipsets installed on some drive enclosure bridgeboards a decade ago. Apple chose to not address the problem, and pointed at the drive manufacturers for fixes -- and history may repeat itself again in this case. The USB 3.0 implementation on the Mediasonic RAID case could be rectified by the vendor with tighter timing, but it could just as easily be fixed by Apple.
MacNN has learned that a new firmware revision in the works for the entire 2012 line of Apple laptops, but it its not known if any fixes regarding USB 3.0 are included. As a coda to the research, it is important to note that most cases and most drives tested have no problems with negotiation and proper communication with a host MacBook Pro, but our conclusion is that low-end or "no-name" brand cases may have USB 3.0 chipsets that cut corners. As always, consumer awareness, research, and checking product warranties before buying is the most prudent option.