The Curious Case of SSD Performance In OS X

mr_sifter writes "As we've seen from previous coverage, TRIM support is vital to help SSDs maintain performance over extended periods of time — while Microsoft and the SSD manufacturers have publicized its inclusion in Windows 7, Apple has been silent on whether OS X will support it. bit-tech decided to see how SSD performance in OS X is affected by extended use — and the results, at least with the Macbook Air, are startling. The drive doesn't seem to suffer very much at all, even after huge amounts of data have been written to it."

Comments

Two quotes stick out

[izomiac]

While skimming the article two parts really stood out. First:

Apple's description of the zeroing format method we used fits the description of what we wanted in terms of resetting the SSD to a clean state

Zeroing is not the same operation as TRIM. TRIM marks a block as unused, and if you read it you'll either get random data, or zeros (probably the later). Zeroing marks it as in-use, and if you read it you'll get zeros. The SSD's wear management algorithm will move the latter around as though it were real data, whereas it knows the former is "empty" so it won't bother (so the SSD will be faster). In other words, they don't seem to be using a "clean state" at all, which would explain why there's no difference.

Secondly, the SSD in the Macbook Air really isn't very fast at all

Which strengthens the hypothesis that they were comparing one "full" state with another. Pop out the drive, TRIM the whole disk in another OS, and run the benchmark again. It'll probably be a lot faster. It wouldn't surprise me if installing the Mac OS at the factory caused every block on the SSD to be used at least once (e.g. a whole disk image was written), which would mean you'd already be at the worse possible performance degradation.

Re:Two quotes stick out

[izomiac]

Well, to be honest I did look a bit more at that part before criticizing it. On page two of the article they elaborate:

The Macbook Air we received from Apple had previously been sent to other reviewers, so we first needed to get the SSD into a "clean" state. While we have an established way of doing with Windows systems - using HDDerase to perform a low level format - we needed to find a way of doing this with OS X. The OS X installer actually allows you to load an app called Disk Utility, which can partition and format the drive - and one of the options is for a format which zeroes all the data.

According to Apple, "the "Zero all data" option... takes the erasure process to the next level by converting all binary in the empty portion of the disk to zeros, a state that might be described as digitally blank." The next level? Count. Us. In.

And the link goes to an Apple site that explains what zeroing the data does and how to do it.

Once we'd done this with the clean SSD, we then proceeded to give it a damn good thrashing. As with our Windows SSD testing, we filled the SSD with around 112GB of files from a USB hard disk - the files included OS files, game installs and media. We then deleted these files, then copied them across again, repeating the process ten times, so that we'd written over 1TB of data to the SSD.

So... they wrote over the whole disk with a format, then copied and deleted a bunch of files in hopes to get full coverage of the disk (i.e. exactly what the zeroing format did). That's about three levels of abstraction above what they're trying to test.