December 09, 2010, 2:06 PM — As you probably know, the MacBook Air uses flash storage instead of the hard drives found in every other Mac. And while the initial results using our Speedmark 6.5 test suite showed that the Air's flash storage helped provide a performance boost, we were concerned about whether that performance could be maintained over time.
Solid state drives (SSDs) and flash storage (Apple doesn't call the Air's flash-based storage an SSD; it doesn't use a 2.5-inch hard drive housing like a conventional SSD) offer a number of advantages. Compared to hard drives, flash-based storage performs faster. And since it lacks moving parts, flash-based storage is more shock resistant and not prone to the mechanical failings that hard drives are susceptible to.
The obvious downsides are that flash-based storage devices are much more expensive from a price per gigabyte perspective, and they offer lower storage capacities.
Not so obvious, however, are the performance issues. The individual data cells on an SSD have a finite number of times that they can be written to, so manufacturers often include wear-leveling technologies to increase the life of the flash memory. Also, write performance can suffer when SSDs begin to fill up over time. Some SSD manufacturers use over-provisioning tactics—setting aside some capacity away from the user to swap for bad blocks and background tasks. Some SSDs offer TRIM, a way of handling some of the trash management duties that can also slow down write speeds, but TRIM isn't supported by Mac OS X.
When shopping for an SSD, you can usually read about the kinds of technologies the manufacturer uses. Apple, on the other hand, doesn't really talk in detail about its behind-the-scenes strategies for dealing with flash memory's shortcomings. That can make people like me nervous— especially in a system like the MacBook Air, where the flash memory is not user replaceable. (Sites like iFixit show how to open up a MacBook Air and access the flash storage, but such a task voids your warranty.)
Flash storage torture tests