Mac OS X update supports SSD optimization

Support for TRIM command will move data reads from random to sequential

The latest version of Apple's Mac OS X operating system supports the TRIM command, which allows built-to-order systems with solid-state drives (SSDs) to perform more optimally.

According to Mac Rumors, the Mac OS X 10.6.8 update announced last week allows TRIM commands to perform a function known as garbage collection, which erases old data marked for deletion.

The command then consolidates existing data on an SSD so that it can be read sequentially and not randomly, which improves read performance.

Users can check for TRIM support using the Apple System Profiler tool.

While many of today's SSDs contain a garbage collection algorithm in their controller's firmware, it can create write amplification, or increased data movement on the NAND flash memory, which causes the drive to wear out more quickly.

Consumer NAND flash, which is used to make SSDs for desktop and laptop systems, typically has no more than 10,000 erase-write cycles, where existing data is first erased and then re-written along with new data. The most expensive single-level cell (SLC) NAND, used in servers, has up to 100,000 erase-write cycles before the drive wears out.

The TRIM command works independently of controller firmware, handling the garbage collection overhead.

Jim Handy, an analyst with market research firm Objective Analysis, said Apple's build-to-order systems will benefit from the TRIM command because the SSDs will no longer need to guess at what is valid data and what is no longer needed by the OS.

"TRIM is used by the OS to give the SSD permission to erase sectors in the background, ensuring that there's plenty of available space for the OS to write to when the OS needs it," he said. "In essence TRIM support will make OS X perform faster in the same hardware simply by assuring that there are no traffic jams in the SSD."

Microsoft Windows 7 also supports the TRIM command, which prompted SSD manufacturers like Intel to add firmware upgrades to their products to take advantage of the command.

Apple also is one of the only companies to make laptops that support the serial ATA 3.0 specification, which allows twice the throughput of SATA 2.0 drive interfaces.

For example, Apple's MacBook Pro, which was released in February, added support for SSDs manufactured with SATA 3.0 interfaces. Most SSDs manufactured today support the SATA 3.0 spec.

Apple Hardware image
The top-end Apple MacBook Pro now uses the SATA 3.0 specification for the internal drive connection, which offers 6Gbps link speed.

Apple has bet big on SSD technology, a trend borne out by the fact that is now ranks as the world's top consumer of NAND flash memory.

Lucas Mearian covers storage, disaster recovery and business continuity, financial services infrastructure and health care IT for Computerworld. Follow Lucas on Twitter at @lucasmearian, or subscribe to Lucas's RSS feed . His e-mail address is

Copyright © 2011 IDG Communications, Inc.

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