Accelsior S Review: Give Your Mac Pro a Performance Boost

Add an Internal Bootable SSD to Your Mac Pro

Accelsior S
The Accelsior S delivers on its promise of top-notch performance at a very reasonable price. Courtesy of Other World Computing

I’ve been using Mac Pros for many years, but with Apple’s change to the cylindrical Mac Pro design in late 2013, it was time to either move to a different Mac model or upgrade my 2010 Mac Pro, to gain performance that would allow me to delay having to replace my trusty Mac.

In the end, I decided to do both. I’m moving on to a new Retina iMac, updating the Mac Pro, and then handing it down to my wife to replace her aging iMac, which has been having display problems.

To help her get the most out of the new (to her) Mac Pro, I thought about removing the performance bottleneck caused by the slower SATA II drive interface and replacing the startup drive with an SSD. Because this should provide a nice boost in performance, I started looking for how to gain the benefits of an SSD without breaking the bank. That meant deciding on both the SSD storage and a way to connect it to the Mac Pro without spending an arm and a leg.

OWC Accelsior S

I decided to use a standard 2.5-inch SATA III (6G) SSD and a PCIe card with a SATA III controller and the ability to mount a 2.5 SSD to the card. There are a handful of such cards that are Mac compatible but I found the Accelsior S by OWC to be nicely priced, with the features I need.


  • PCIe 2.0 x2 provides enough bandwidth for SATA III SSD.
  • Half-height, half-length card for easy installation.
  • ASMedia 1062 controller doesn't require any drivers for use with OS X.
  • Bootable.


  • OS X considers a drive connected to Accelsior S to be an external.
  • Can't be used for Boot Camp.

The Accelsior S is one of the least expensive SATA III cards available for the Mac Pro. It supports a single 2.5-inch drive mounted to the card and connected by a standard SATA III connection. While other SATA III cards include multiple SATA connections, the Accelsior S single SATA III port is available at a significantly lower cost.

In fact, it's low enough that if we should ever need a second SSD, we can easily purchase a second card, and still be near, or even lower than, the cost of some competitors' dual-port cards.

Installing the OWC Accelsior S Card

The Accelsior S card is delivered with just an install guide and a set of four screws for mounting a 2.5-inch drive (not included). The most difficult part of the installation is picking an SSD brand and size to mount to the card. I selected a 512 GB Samsung 850 EVO that happened to be on sale.

Installation is a two-step process that begins with mounting the 2.5-inch drive to the Accelsior S by sliding the SSD (or any 2.5-inch drive) into the SATA connector on the card. Then, while flipping the card over, use the four included screws to secure the drive to the card.

With the drive secure, the second step is to install the Accelsior S card in your Mac Pro.

Start by shutting down your Mac Pro and then removing the side access plate. Remove the PCIe card slot bracket, and install the card into an available PCIe slot. For best performance, you should choose a PCIe slot that supports four lanes of traffic. In the case of the 2010 Mac Pro, all available PCIe slots will support at least four lanes.

Earlier Mac Pro models had specific lane assignments by PCIe slot, so be sure to check your Mac Pro manual.

Reconnect the PCIe card slot bracket, and close up the Mac Pro. That’s all that's needed for installation.

Using the Accelsior S

We're using the Accelsior S and the SSD that's attached to it as the startup drive. Once I formatted the SSD, I cloned the existing startup to the new SSD using Carbon Copy Cloner. I could just as easily have used SuperDuper, or even Disk Utility, to clone the startup information.

I also took the time to move the user data to one of the available internal hard drives.

This ensures that the SSD will always have enough free space to ensure optimal performance.

Accelsior S Performance

I used two drive benchmarking utilities: Disk Speed Test from Blackmagic Design, and QuickBench 4 from Intech Software. The results from both benchmarking apps showed that the Accelsior S was able to deliver very close to what Samsung says is the top-end speed for sequential writes and sequential reads. In fact, this is probably the closest I've ever come to actually matching a manufacturer's speed claims. The point being, the Accelsior S isn't going to inhibit the performance of the drive connected to it.

Accelsior S Performance
Benchmark UtilitySequential WritesSequential Reads
Disk Speed Test508.1 MB/s521.0 MB/s
QuickBench510.3 MB/s533.1 MB/s
Samsung Spec520 MB/s540 MB/s

TRIM and Boot Camp

As mentioned in the cons, the drive connected to the Accelsior S is considered to be an external drive. However, that doesn't impact making use of TRIM support, if you wish to. While it's true that TRIM won't work for external USB-based SSDs, it works fine with the Accelsior.

Unfortunately, while TRIM will work, Boot Camp won’t. The problem here is that the Boot Camp utility that partitions and helps install a Windows environment will fail on the installation process since it sees the target device as an external drive. When it first created Boot Camp, Apple decided not to support installation on external drives. And although Windows itself will work from an external drive, Boot Camp won't allow the install process to proceed.

Final Thoughts

For me, Boot Camp was the only negative I really found with the Accelsior S, and even so, I don’t consider it much of a negative since I have no desire to run Windows from the SSD. If I need Windows, I can use Boot Camp to install it on one of the other internal hard drives in the Mac Pro.

The Accelsior S delivers on its promise of top-notch performance at a very reasonable price. It doesn't get in the way of delivering what the top end of today's SATA III-based SSDs can deliver, and in the end, that's the best recommendation of all.

Published: 7/16/2015

Updated: 7/29/2015

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