OWC Mercury Accelsior E2: Review - Mac Peripherals

Performance, Versatility, and Upgradability: Who Could Ask for Anything More?

Mercury Accelsior E2 Review
OWC Mercury Accelsior E2 PCIe. Courtesy of Other World Computing

Other World Computing recently updated its Mercury Accelsior PCIe SSD card (reviewed as part of the OWC Mercury Helios PCIe Thunderbolt Expansion Chassis) to include two external eSATA ports. In addition to new ports, the card also got a new name: Mercury Accelsior E2 PCIe.

Because of the new eSATA ports, I wanted to get my hands on one of these cards and put it to the test. OWC was very accommodating and sent me the new Mercury Accelsior E2 card with a 240 GB SSD installed. But they didn't stop there. Along with the card, OWC sent an external eSATA case (Mercury Elite Pro-AL Dual SATA) outfitted with two 240 GB Mercury Extreme Pro 6G SSDs.

This configuration should let me not only test the performance of the two eSATA ports but also, by creating a RAID 0 array of all of the SSDs, test the maximum performance possible from the Mercury Accelsior E2 PCIe card.

If you want to know how the card performed, read on.

OWC Mercury Accelsior E2 Overview

The OWC Mercury Accelsior E2 may be one of the best performance and storage upgrade options for Mac Pro owners. That's because the Accelsior E2 provides a pair of OWC's SSD blades configured in a RAID 0 array, as well as two 6G eSata ports that can be configured with conventional hard drives or additional SSDs.

The Mercury Accelsior E2 is a low-profile two-lane PCIe card with a Marvel 88SE9230 SATA controller taking care of the PCIe interface and the four SATA ports. The Marvel SATA controller supports data encryption as well as hardware-based RAID 0,1, and 10 arrays. OWC configured the controller for RAID 0 (striped) and 128-bit AES data encryption for the two internal SSD blades, and independent SATA channels for the two external eSATA ports. The end user can't change the controller's predefined configuration; however, as we discovered in our performance testing, this may be the best possible configuration for the card.

Although the Accelsior E2 can be purchased without the two internal SSD blades installed, most individuals will probably opt for one of the configurations that include SSD. All of OWC's SSD blades use the SandForce SF-2281 series of SSD controllers, with 7% over-provisioning.

Our review model was factory configured with two 120 GB SSD blades in a RAID 0 array.

Because the Marvel controller appears to the Mac as a standard AHCI (Advanced Host Controller Interface) device, there are no drivers to install. Also, the internal SSD storage and any devices connected to the external eSATA ports are bootable.

OWC Mercury Accelsior E2 Installation

Installing the Accelsior E2 is about as straightforward as it gets with a PCIe card and a Mac Pro. Be sure to follow standard procedure for installing a static-sensitive device, such as using an anti-static wrist strap.

If you have a 2009 or later Mac Pro, you can place the card in any available PCIe slot without worrying about performance or having to configure the slot lane assignments.

The 2008 Mac Pros have a mixture of PCIe 2 16-lane slots and PCIe 1 4-lane slots. In order to ensure the best performance, the Accelsior E2 card must be installed in one of the 16x lanes. You can use the Expansion Slot Utility included with earlier Mac Pros to configure lane speeds.

If you need to install SSD blades, be sure you're properly grounded before handling the card or the blades. The SSD blades slide into their connectors quite easily. Once it's installed, make sure the blade is seated over the containment post at the opposite end of the card.

If you're moving a pair of SSD blades from another card, be sure the blade in slot 0 is installed in the new card's slot 0; likewise, install the slot 1 blade in slot 1 of the new card.

Once the blades and card are installed, you're ready to boot up your Mac Pro and enjoy the performance increase.

OWC Mercury Accelsior E2 Internal SSD Performance

Once we finished installing the Accelsior E2, we quickly buttoned up the Mac Pro and booted it. The Accelsior was readily recognized and mounted without problems on the Desktop. Although the installed SSDs were preformatted, we fired up Disk Utility, selected the Accelsior SSDs, and erased them in preparation for benchmarking.

As expected, the Accelsior SSD showed up in Disk Utility as a single drive. Even though there are two SSD blades installed, the hardware-based RAID presents them to the end user as a single device.

Testing Accelsior E2 Internal SSD Performance

We tested the Accelsior E2 on two different Macs; a 2010 Mac Pro configured with 8 GB of RAM and a Western Digital Black 2 GB drive as the startup device, and a 2011 MacBook Pro. We used the MacBook Pro's Thunderbolt port to connect to the Accelsior E2 through the Mercury Helios Expansion Chassis.

This allowed us to not only test native performance directly on the Mac Pro's PCIe bus, but also to see if the Helios Expansion Chassis that we tested earlier would benefit directly from an upgrade to the Accelsior E2 card.

Accelsior E2 Performance in the Helios Expansion Chassis

We used Drive Genius 3 from ProSoft Engineering to measure random and sustained read and write performance. We wanted to find out if there were any substantial performance differences between the original Accelsior card we tested as part of the Mercury Helios Thunderbolt Expansion Chassis review and the new E2 version.

We didn't expect any performance differences; after all, they're the same card. The only difference is the addition of two external eSATA ports. In our initial bench test, we saw only a marginal performance difference that would never be detectable in real-world use and can be attributed to normal variances in chip performance.

With that out of the way, it was time to move on to more extensive bench testing in the Mac Pro.

Accelsior E2 Performance in a 2010 Mac Pro

To test how well the Accelsior E2 performed, we used Drive Genius 3 for reading/write performance tests. We also used Blackmagic Disk Speed Test, which measures sustained write and read performance with video frame-sized data chunks from 1 GB to 5 GB in size. This provides a good indication of how well the storage system will work for video capture and editing tasks.

Drive Genius 3 benchmark tests were impressive, with both random and sustained write speeds able to top 600 MB/s, and random and sustained read speeds pushing past 580 MB/s.

  • Peak Random Write: 608.330 MB/s
  • Peak Random Read: 581.332 MB/s
  • Peak Sustained Write: 641.54 MB/s
  • Peak Sustained Read: 585.598 MB/s

Blackmagic's Disk Speed Test reports results as sustained write and read speeds. It also lists the video formats and frame rates that the drive under testing can support for capture and editing. We ran the test for video data sizes of 1 GB, 2 GB, 3 GB, 4 GB, and 5 GB.

5 GB Test Size

  • Write: 495.0 MB/s
  • Read: 621.7 MB/s

4 GB Test Size

  • Write: 491.5 MB/s
  • Read: 627.4 MB/s

3 GB Test Size

  • Write: 498.8 MB/s
  • Read: 640.7 MB/s

2 GB Test Size

  • Write: 502.5 MB/s
  • Read: 596.5 MB/s

1 GB Test Size

  • Write: 502.9 MB/s
  • Read: 555.4 MB/s

The Accelsior E2's internal RAID 0 SSD's performance was very impressive, but it's only half the story of the E2 version of this card. To complete our benchmarks, we needed to test the two eSATA ports, and then benchmark the Accelsior E2 with all ports in use at the same time.

OWC Mercury Accelsior E2 eSATA Port Performance

The Accelsior E2 has two eSATA ports that can be connected to your favorite external eSATA enclosure. This gives the Accelsior E2 a great deal of versatility, allowing a single card solution to provide internal RAID 0 SSD as well as two ports for external expansion.

If you're thinking that this card might be a great way to either increase the performance of your current Mac Pro or, with the addition of an external PCIe expansion cage, provide additional high-performance storage to a new 2013 Mac Pro, then we're thinking alike. I was eager to benchmark the eSATA ports.

Testing was performed using the same 2010 Mac Pro and the Accelsior E2 card. We also used a Mercury Elite Pro-AL dual drive enclosure equipped with a pair of 240 GB OWC Extreme Pro 6G SSDs. Each SSD was connected independently (no RAID) to one of the eSATA ports on the card.

Drive Genius 3 Benchmark Results (Independent eSATA Port):

  • Peak Random Write: 444.605 MB/s
  • Peak Random Read: 443.914 MB/s
  • Peak Sustained Write: 442.502 MB/s
  • Peak Sustained Read: 448.720 MB/s

Individual eSATA port performance was close to what we expected. A 6G eSATA port should be able to provide a burst speed around 600 MB/s. That number comes from the native port speed of 6 Gbit/s minus the overhead of 8b/10b encoding used in the 6G specifications, which should produce the burst speed maximum of 4.8 Gbit/s or 600 MB/s. However, that's only the theoretical maximum; each SATA controller will have additional overhead to handle.

Although the Accelsior E2 doesn't allow the two external eSATA ports to be used in a hardware-based RAID, there's nothing to prevent you from using a software-based RAID solution. Using Disk Utility, we reformatted the two OWC Extreme Pro 6G SSD/s into a RAID 0 (striped) array.

Drive Genius 3 Benchmark Results (RAID 0):

  • Peak Random Write: 673.968 MB/s
  • Peak Random Read: 659.332 MB/s
  • Peak Sustained Write: 683.79 MB/s
  • Peak Sustained Read: 651.121 MB/s

The RAID 0 configuration of the eSATA ports brought the throughput performance very close to the maximum (688 MB/s) for our 2010 Mac Pro.

I couldn't resist seeing if we could saturate the Accelsior E2 by creating a software RAID 0 between the internal SSD and the two External Mercury Extreme Pro 6G SSDs.

Now, this isn't a scientific benchmark; there are many problems with trying to do this. First, the two internal SSD blades are already in a hardware-based RAID 0, which can't be changed. While we can add them as a slice in a software-based RAID, they will only act as a single RAID slice. So, instead of being able to use four slices in our RAID 0 (two internal SSDs and two external SSDs), we'll only see the benefit of a three-slice RAID set. That should still be enough to tax the Accelsior E2 in a 2010 Mac Pro.

Drive Genius 3 Benchmark Results (All Ports RAID 0)

  • Peak Random Write: 716.958 MB/s
  • Peak Random Read: 696.204 MB/s
  • Peak Sustained Write: 710.953 MB/s
  • Peak Sustained Read: 695.38 MB/s

As expected, the Accelsior E2, in combination with a 2010 Mac Pro, hit the wall in terms of throughput. OWC's specifications for the Accelsior E2 list 688 MB/s maximum throughput when the card is installed in a 2009 through 2012 Mac Pro, and it appears that the specs are accurate. Still, it was worth a shot.

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OWC Mercury Accelsior E2 and Fusion Drives


As noted on the previous page, the Mercury Accelsior E2's performance was right in line with what we expected. And that means the Accelsior E2 deserves to be installed in just about any Mac Pro, especially if a fast SSD RAID for a startup drive and a pair of 6G eSATA expansion ports are to your liking; they certainly are to mine.

The fact that the internal RAID 0 SSD and external eSATA ports are all bootable without installing any drivers, and that the Mac Pro sees the card as a standard AHCI controller, made me wonder about yet another possible use for the card, as part of a Fusion-based storage system.

Apple's Fusion drive uses a fast SSD and a slower drive that are logically combined into a single volume. The OS X software moves frequently used files to the faster SSD, and less often used items to the slower drive. Apple doesn't recommend using any external drives as part of a Fusion volume, but the Accelsior E2's internal SSD and external eSATA ports are all managed by the same Marvel controller. I expected this to allow me to bypass any latency issues that Apple was worried about in using an internal SATA-connected drive and an external USB or FireWire device.

I used Terminal and the method outlined in Setting Up a Fusion Drive on Your Current Mac to create a Fusion drive composed of the internal RAID 0 SSD and a 1 GB Western Digital Black hard drive connected to one of the eSATA ports.

I ran this Fusion volume for a week without any issues, and enjoyed the performance boost of the Fusion configuration. If it suits your needs, keep this in mind as another possible use for the Mercury Accelsior E2.

OWC Mercury Accelsior E2 - Conclusion


The Accelsior E2 is very versatile. It provides incredibly fast performance from the internal SSDs in a RAID 0 array, and the capability to add more storage with the two eSATA ports.

While almost all of our testing and review process was performed with the card installed in a Mac Pro, we want to note that the Accelsior E2 card is now included in the Mercury Helios PCIe Thunderbolt Expansion Chassis, which we reviewed earlier, when it used the older Accelsior card without the eSATA ports. That's a nice upgrade for the Helios, and an important product to consider when the new 2013 Mac Pros appear, because they only permit external expansion using Thunderbolt or USB 3.

While we've been liberally praising the Accelsior E2, there are some things to know before you decide if the card is right for you.

The 2009-2012 Mac Pros can deliver throughput up to the specified maximum of 688 MB/s no matter which PCIe slot you choose to use for the card. Every other Mac has restrictions, as you'll see below.

In 2008 Mac Pros, the card must be installed in one of the two 16-lane PCIe slots to reach maximum throughput. If the card is installed in any other PCIe slot, the throughput will fall to around 200 MB/s.

2006-2007 Mac Pros are limited by the PCIe 1.0 bus to around 200 MB/s throughput. If you have a 2006-2007 Mac, you would actually see better performance by installing an SSD in an internal drive bay.

Thunderbolt-equipped Macs that use the Accelsior E2 in a Thunderbolt 1 expansion chassis should see very nearly the same performance as a 2009-2012 Mac Pro.

The Accelsior E2 uses a two-lane PCIe 2.0 connection, which can't provide enough throughput to feed all ports (internal SSD and external eSATA) simultaneously. We observed this when we attempted to create a RAID 0 array of both the internal and external devices.

OWC Mercury Accelsior E2 - Final Thoughts


We were very impressed by the Accelsior E2 card. The card can be purchased with or without the internal SSD blades installed. The SSD blades are available separately, so you can upgrade the amount of SSD storage at any time. OWC will even provide a credit if you return smaller SSD blades when you upgrade to larger sizes. Additionally, OWC offers a credit for customers with the older Accelsior card who wish to upgrade to the Accelsior E2 card.

While pricing tends to change over time, current prices as of June 2013 are as follows:

  • Accelsior E2 0 GB (no SSD blades): $199.99
  • Accelsior E2 120 GB (2 64 GB blades) $319.99
  • Accelsior E2 240 GB (2 120 GB blades) $477.99
  • Accelsior E2 480 GB (2 240 GB blades) $734.99
  • Accelsior E2 960 GB (2 480 GB blades) $1,299.99

If you want to expand your Mac Pro's storage capability and break through the SATA II barrier imposed by the older drive interface used in 2012 and earlier Mac Pros, it's difficult to argue against making the Mercury Accelsior E2 the heart of your storage system.

This single-card solution provides a fast RAID 0 internal SSD and two external 6G eSATA ports. The only limits on your Mac's storage system will be your imagination (and budget).

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