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BARE FEATS LAB - real world Mac speed tests

REVIEW: Magma's ExpressBox 3T
Thunderbolt to PCIe Adapter Chassis

Originally posted Friday, February 8th, 2013, by rob-ART morgan, mad scientist
February 21st, 2013, added results for SeriTek/Q6G in first graphs below.

Magma has a PCI Express expansion chassis that connects to the Thunderbolt port of your Mac. It's called the ExpressBox 3T. Key features include:

  • Three full length PCI Express 2.0 slots. Two are rated at x8 and one at x4. Supports x1, x4, x8, and x16 PCIe adapters.
  • Power feeds are available to adapters that require more than bus power.
  • The list of compatible PCIe adapters includes video capture, audio, iSCSI, SATA, SAS, SAN, Fibre Channel, SSD, and Network -- 128 adapters in all.
  • A second Thunderbolt port enables you to daisy chain up to 6 other Thunderbolt devices.
  • Hot swappable cooling fan; additional blower for extra hot running adapters.
  • Money back guarantee -- one year return to factory

What transfer speeds are possible with the ExpressBox 3T?
We created a RAID 0 set of four 6Gbps SSDs and connected them to the ATTO ExpressSAS R644 6Gbps x8 SAS/SATA RAID adapter. The graphs below show the large sequential transfer speed with the ExpressBox 3T ("TB exp") versus the same setup in the 2010 Mac Pro ("mac pro"). The transfer speeds are twice as fast on the Mac Pro. Why? Limited bandwidth of Thunderbolt.

In the graph below, we added the results for two 6G SSDs in a miniSwap/ES enclosure connected to the FirmTek SeriTek/Q6G 6G 4 port, 6G eSATA adapter. Note how this setup (labeled "Q6G TB exp" in the graphs below) comes in transfer speed to the more expensive, higher bandwidth ATTO R644 with four 6G SSDs. How can a 2x $200 eSATA adapter with two 6G SSDs rival the speed of an 8x $1000 mini-SAS adapter with four 6G SSDs? The answer: limited bandwidth of Thunderbolt.

Insight #1: The limited bandwidth of Thunderbolt in relation to generation 2.0 of PCI Express bus keeps high-end, high bandwidth PCIe adapters from running at the full speed. Though the adapter's throughput may be rated as high as 77Gbps in full duplex mode, the maximum bandwidth attainable through the Thunderbolt "conduit" is 10Gbps.

What happens to transfer speeds when two devices inside of or connected to the ExpressBox 3T are active at the same time?
We mounted two OWC Accelsior SSD adapters in the ExpressBox. Then we daisy chained a LaCie Little Big Disk Thunderbolt enclosure to the box. We benchmarked the Accelsiors as a single card and as a dual card RAID 0 set. Then we ran those benchmarks again, this time with the LaCie LBD TB transferring data simultaneously. Note the Accelsior's drop in speed for the graph entries labeled "simu." We saw the same drop in speed when using two storage host adapters simultaneously which were installed inside the ExpressBox 3T.

Insight #2: The 10Gbps bandwidth of the Thunderbolt 'limited' ExpressBox 3T is shared by all devices -- unlike the PCIe bus in the Mac Pro where the four PCIe slots run in parallel.

Though the Magma ExpressBox 3T enables you to preserve your investment in PCIe adapters when moving from a Mac Pro to an iMac or MacBook Pro or Mac mini, there are limitations you must accept in doing so.

  • The performance of your PCIe adapters is limited to the 10Gbps bandwidth of the Thunderbolt port to which the ExpressBox 3T is connected. And that bandwidth is shared by all adapters inside and all devices daisy chained to the ExpressBox 3T.
  • Graphics Processing Units (GPUs) are not supported by the ExpressCard 3T at this time. Even if that support comes, the performance of a high-end x16 GPU that is "accustomed" to 64Gbps bandwidth will be limited to Thunderbolt's 10Gbps bandwidth (or x2.5).
  • The fan is a welcome cooling agent but at 47dB, it is noticeable -- but not any more than the idling fans of a Mac Pro.
  • The price starts at $979. If you only need one slot, there are companies that make less a costly Thunderbolt expansion chassis. However those less costly boxes take only half length adapters and provide only bus power.

The strength of the Magma ExpressBox 3T is its ability to make your PCIe adapters function with any Mac with a Thunderbolt port. Some professionals need to work in remote locations. Rather than schlep their Mac Pro to that location, they can pull the storage adapters or video/audio adapters out of their Mac Pro, install them in the ExpressBox 3T, and connect it to a MacBook Pro. During our comparative testing, we moved the ATTO ExpressSAS R644 RAID adapter back and forth between the Mac Pro and a 2012 iMac connected to the ExpressBox 3T. When the ExpressBox 3T and drive enclosure were powered up, the four SSD RAID 0 set mounted instantly and was ready to go.

And though we demonstrated the limits of the transfer speeds over Thunderbolt, those speeds are fully adequate for many video and audio applications. Magma states that there is sufficient bandwidth for audio DSP with Pro Tools. Also Red uses ExpressBox 3T to run Red Rocket cards on their Thunderbolt Macs for all of their "Reducation" tours.

Feedback or comments? Contact me , mad scientist.
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copyright 2013 Rob Art Morgan
"BARE facts on Macintosh speed FEATS"