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2013 Mac Pro: Choosing PCIe Flash Drive Capacity

Get Mac Pro at B&H Photo. See also MPG’s computer gear wishlist as well as diglloyd-recommended performance packages for Mac Pro.

The 2013 Mac Pro offers a single internal slot for PCIe flash storage (fast). This slot is filled by Apple with a 256GB / 512GB / 1TB module as chosen by the buyer at time of purchase.

In Apple parlance, SSD = flash drive. The terms are equivalent.

The SSD module is user-replaceable, with upgrade solutions likely to emerge by mid 2014. The quality, speed, longevity and capacity are all buying factors, and buyers are advised not to make assumptions on those points when upgrading.


  • Choose a capacity that allows at least 20% free space to remain when filled up with Your Stuff: 200GB on a 256GB*, 400GB on a 512GB, 800GB on a 1TB. This avoids performance losses from file system inefficiencies as well as any internal SSD housekeeping behaviors.
  • Users looking for peak performance and long-term longevity should be looking at a 30% free space target to reduce flash write wear, e.g. 350GB max used on a 512GB* SSD. But it all depends: heavy write activity over a long time wears flash; mostly read activity is benign.

While 256GB* is more than adequate as a boot drive for most uses, many users end up dropping all sorts of stuff on the boot drive, simply by default. Then one day, “drive full” pops up at an inopportune time.

For speed and simplicity, the 1TB option might be entirely sufficient in capacity for some users to store all their data. All users can add on various USB3 SSDs or Thunderbolt SSDs but few of these will approach the speed of the internal PCIe flash, though PCIe SSD cards housed externally should offer similar performance.

* 256GB likely really means 256K flash with 250GB usable capacity (some of the flash is set aside for failure recovery). Traditionally Apple’s claims of capacity have been misleading in terms of available usable capacity. It’s not a big difference, but if that pound of lobster you bought at the store was really .977 pounds, would you not be a little surprised? OWC SSDs are honest about actual usable capacity: SSDs with 256GB of flash memory are honestly designated as 240GB, 512GB flash is 480GB, 1024GB flash is 960GB.

What to put on the SSD ?

Use the SSD for performance-sensitive tasks and files.

  • Put original image files, video files or sound files on a separate “Master” volume, and back up both with cloning. Such files have low performance requirements.
  • Put Adobe Lightroom Catalog folders on the SSD, Photoshop scratch, cache folders, temporary working files, etc. This gets disk I/O out of the way and allows the CPU to operate with minimal delay.

If in doubt, watch Activity Monitor to see how much disk I/O is going on along with CPU usage.


Unlike the MacBook Pro which has base configuration of 512GB, the 256GB base option in the Mac Pro is apparently designed to ramp up the selling price so that the $2999 model will carry a notably higher price tag to gain the 512GB option. Cynical perhaps, but the Mac Pro is a premium machine and yet half the flash storage is offered even for the 6-core.

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