Daniel Eran Dilger
While Apple has already started incorporating SSDs into its Macs, it hasn't yet added TRIM, a specific type of operating system support intended to coordinate disk use between the system and the SSD controller. The feature was previously detailed as having "no" support in System Profiler (below, top).
The new Lion developer preview is reported to add TRIM support however, with users of Apple SSDs noting a "yes" (actually "oui") for support according to a report by the French blog MacGenerations (below, bottom).
Unlike conventional magnetic hard drives, SSDs must be erased before being rewritten with new data, somewhat similar to CD-RW disc. This housekeeping task can be managed by some SSD controllers, but the TRIM command is designed to keep SSDs efficiently optimized at all times, preventing a gradual decline in performance as garbage stacks up.
Cleaning up unused bits of deleted files on SSDs requires a sophisticated balancing act between making sure the drive is clean and ready for new write operations, while also limiting unnecessary wear, as the flash cells used by the devices wear out relatively quickly after a finite number of erase/write cycles, compared to the very long life of the recording surfaces of magnetic storage disks.
The TRIM command is part of the ATA interface standard. So far, it appears Apple's support in Lion is only activated for SSDs shipped by the company and not third party devices, but this is likely to be fleshed out more as Lion develops.
Christine McKee
Charles Martin
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63 Comments
I remember a friend who worked at Apple relating a story about the early LaserWriters - the utility could rename any one of them, and the name was stored in the unit in flash memory. A favorite pastime at Apple seemed to be renaming others' LWs so you never really knew where you were printing to - your recipes could come out of the boss' printer, you could suddenly be printing to a machine with a less-than-appropriate name, etc. I got an AppleLink message one day bleakly reporting that we should know you can only rename a LW 256 (?) times and after that it's stuck with that name. The lack of further detail suggested it as not a particularly happy discovery.
Good news - about time really.
trim is very much required with all the flash going into apple notebooks. I thought they had implemented some rudimentary garbage collection behind under the hood, but unfortunately they haven't. The quality drop in my air ssd (11") is considerable without it.
How do SSD drives handle the situation when the memory cells wear out and are no longer writable? What happens to user data on the drive?
Will the SSD drive also start showing a decline in storage capacity when viewed in the OS?
does anything equivalent have to be implemented on non-ssd flash storage? for example the flash memory on our iPhones?