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Promise Pegasus R6 12 TB

Nine External Thunderbolt Storage Devices, Rounded Up

Pegasus R6 6 TB
Pegasus R6 12 TB
6 x 1 TB
6 x 2 TB
Hard Drive
Hitachi 7K1000.DHitachi 7K3000
Price (MSRP)

Sporting six hot-swappable bays, Promise’s Pegasus R6 is the top dog when it comes to performance-oriented Thunderbolt-based storage solutions. Intel and its partners commonly use this device to demonstrate what the technology is capable of achieving, and the R6's high price makes it even more exclusive. The entry-level 6 TB (6 x 1 TB) model will set you back $1800, and the 12 TB version commands a $2500 price tag.

You get what you pay for, though, and the Pegasus R6 demonstrates its suitability in business-class environments with a serial port for uninterruptible power supply support at the back of the chassis.

Promise sent us its 12 TB Pegasus R6, employing six 2 TB Hitachi 72K300 hard drives (the 6 TB variant is equipped with Hitachi’s 7K1000.D series). The drive bays are well-designed, featuring sturdy aluminum face plates and large release buttons that make it easy to swap storage out in the event of a disk failure.

The picture above, turned upside-down for better clarity, shows the interior of the Pegasus R6, where we find a 250 W power supply driving a motherboard with PMC-Sierra’s PM8011 PCIe SAS 6Gb/s RAID controller. The PM8011 is actually an eight-lane controller. But because Thunderbolt only enables a PCIe x4 uplink, the other four lanes aren't used.

It's interesting that Promise populates the SAS controller with SATA-based hard drives, though not entirely surprising given the premium SAS-capable disks would have added. You can look at the daughtercard's connectors, though, and see the full SAS interface that accommodates SATA disks, too. SAS 6Gb/s and SATA 6Gb/s both enable similar data rates, so there's no concern over compromised performance. We think that Promise's decision to arm its enclosure with SATA storage was the right one. However, should the company wish to offer a version of its R6 with nearline SAS drives in the future, that could become a possibility.

The R6 supports RAID 0, 1E, 5, 6, 10, and 50. However, we're narrowing our focus to the three configurations we feel are most attractive on a device like this: RAID 0, RAID 1E, and RAID 5.

The R6 really stretches its legs when we measure sequential read performance in RAID 0. It falls just 50 MB/s short of the 1 GB/s barrier at a queue depth of 16! If redundancy is more important to you than blistering speed, RAID 1E operates effectively as three RAID 1 arrays, which is why sequential read performance falls to ~315 MB/s. RAID 5 is a fair compromise, enabling block-level striping with distributed parity. We see sequential reads top out around ~780 MB/s in that arrangement.

This is the only device we're reviewing with performance characteristics that look a little different under OS X than Windows, and there's a reason why. Originally, Thunderbolt allowed device I/O and display signaling to share bandwidth over both bi-directional channels. However, in the summer of 2011, Apple and Intel decided to put device I/O on its own channel in order to preserve the display's signal integrity under heavy workloads.

Prior to that, we were able to achieve close to 920 MB/s in RAID 0 on our 15” MacBook Pro. However, since we "upgraded" to a 13.3” MBP, our new results seem to suggest a ceiling around ~800 MB/s. Promise tells us it sees slightly better performance on PCs, but the delta should only be a few percent at most. Our numbers require more Mac-specific testing, since we don’t know whether it was the update or our system to blame.

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