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Sustained Transfer Speed, Single and Striped (2013 Mac Pro)

OWC Mercury Accelsior Pro Q PCIe SSD

Tested on 2013 Mac Pro 3.3 GHz 8 core with 64GB memory The two Accelsior Pro Q units were in OWC Helios enclosures, each on its own separate Thunderbolt 2 bus (2013 Mac Pro has 6 Thunderbolt 2 ports on 3 busses). This dual setup allows the striped RAID to run at full Thunderbolt 2 bandwidth.

The sustained transfer speed metric is a strong indicator for judging performance for real-world tasks that need high bandwidth.

Sustained transfer speed

Tested using the fill-volume command of diglloydTools DiskTester.

This graph shows sustained transfer speed with 128 MiB transfers across the entire volume capacity (2TB for single unit, 4TB for striped pair). Actual transfer speeds are not usually this high, because many programs do a poor job of utilizing optimal transfer sizes, e.g., Photoshop’s scratch disk behavior.

Performance in a PCIe slot on a 2010/2012 Mac Pro and/or PC might be significantly higher than shown here; MPG did not have a suitable 2010/2012 Mac Pro available for testing.

A single Accelsior Pro Q runs just slightly below the maximum bandwidth of the Thunderbolt 2 bus and is throttled by the Thunderbolt 2 bus for reads—outstanding performance which exceeds that of the internal 2013 Mac Pro SSD. It cannot get any better for read speeds because the bus is saturated.

A striped pair of Accelsior Pro Q runs almost twice as fast as a single unit, which is doubly outstanding and speed far in excess of what most programs can fully utilize.

Single Write: 1212 MiB/sec = 1271 MB/sec
Single Read: 1359 MiB/sec = 1425 MB/sec
Striped Write: 2375 MiB/sec = 2491 MB/sec
Striped Read: 2674 MiB/sec = 2804 MB/sec

Units: MiB = 1024 * 1024, MB = 1000 * 1000

OWC Accelsior Pro Q sustained transfer speed in OWC Helios enclosure on 2013 Mac Pro

Sustained transfer speed on late 2015 iMac 5K

The late 2015 iMac 5K has only two Thunderbolt 2 ports on a single bus.

A single Accelsior Pro Q runs at very similar but slightly slower speeds as the Mac Pro, still very close to the Thunderbolt 2 maximum bus speed for reads.

A striped pair of Accelsior Pro Q is severely throttled by the Thunderbolt 2 bus. Accordingly, write speeds bump up to the bus speed limit and reads improve marginally. The RAID offers very little benefit other than doubling the capacity. This then is the promise of Thunderbolt 3 on future Macs (it doubles the bandwidth of Thunderbolt 2).

Single Write: 1175 MiB/sec = 1232 MB/sec
Single Read: 1323 MiB/sec = 1388 MB/sec
Striped Write: 1360 MiB/sec = 1426 MB/sec
Striped Read: 1337 MiB/sec = 1402 MB/sec

Units: MiB = 1024 * 1024, MB = 1000 * 1000

OWC Accelsior Pro Q sustained transfer speed in OWC Helios enclosure on 2013 Mac Pro
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