Using TRIM for aftermarket Mac SSDs

Be sure to set up TRIM on a Mac that has an aftermarket SSD.

In addition to speedy performance and immunity to fragmentation issues, SSD drives also have long life​ spans. Still, the flash-based NAND storage used in many SSDs has a few design oddities that can slow down performance after prolonged or heavy usage. Fortunately, TRIM commands can clean up an SSD for more consistent long-term functioning, although end-users must ensure that both their drive and their computer operating system support these protocols.

The biggest potential weakness in using an older SSD resides in how it communicates with its host computer. For example, deleting a file typically results in a PC or Mac indicating that the space once occupied by the item is now free and writable. However, the computer's approach to storage management is not mirrored by the SSD, according to Tom's Hardware contributors Manuel Maserio and Achim Roos.

The drive continues to regard freed space as occupied, since its storage is designed for new items to simply overwrite old ones. As such, by default it does not permanently delete anything, which does not cause any problems until it runs out of storage blocks that have never had any data written to them. At that point, it begins overwriting data on old blocks, a process that can cause performance issues that TRIM is designed to mitigate.

"This is where the TRIM command comes into play," explained Maserio and Roos. "When a file is deleted, the operating system sends a TRIM command to the SSD, marking those sectors as invalid data. At that point, the drive knows not to perform garbage collection on them."

Without TRIM, an SSD could prematurely wear out its NAND cells by keeping blocks in garbage collection for long periods. Writing for Techgage, Rob Williams stated that a TRIM operation on the entire SSD can nearly bring it back to original performance levels.

TRIM and Macs
TRIM is now standard for SSDs, and commands are easy to implement in Windows and Linux PCs. However, managing TRIM can be complicated in the case of installing an aftermarket SSD on a Mac. On older MacBook models, a user can install a second drive by swapping out the computer's internal optical drive, but only OEM SSDs have TRIM support from OS X.

There is a simple workaround to the issue, which TechRadar contributor Matthew Bolton explained in an overview of Mac-compatible SSDs. Mac users can install a software solution called Trim Enabler, which lets most drives communicate properly with the operating system.

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