Skip to main content

How SSD performance deteriorates over time

At Apple's 'Back to the Mac' event last Wednesday, the company's CEO Steve Jobs enthused that the new MacBook Air he'd unveiled during his keynote was the "future of the notebook."

Aside from its razor-thin form factor, the new Air's marquee feature is that all models come standard with solid-state disc (SSD) flash memory-based data storage drives instead of the traditional hard disk drives (HDD) such as those made by Seagate, Western Digital, Hitachi, and others.

However, the formidable Mr Jobs may be a bit premature in his declaration, at least as far as a wholesale SSD revolution goes... or perhaps not.

During Seagate Technology's first quarter earnings conference call that same day - a transcript of which has been posted to the web by Seeking Alpha - Seagate CEO Steve Luczo contradicted Jobs's prediction when answering a question tabled by Ben Reitzes of Barclays Capital. He asked if Luczo agreed with Jobs' presumed assertion that all notebooks would be moving toward SSDs and away from HDDs.

Luczo said: "Steve sits in a position that only Steve sits in." He added that, historically at least, the percentage of Apple systems sold with SSDs versus HDDs is a tiny fraction, possibly fewer than three per cent and certainly under five per cent of total sales volume.

Luczo noted that he's had a first-generation MacBook Air with an SSD for about a year and half, and while certain things about it are very nice, others are frustrating, such as the price and lack of SSD storage capacity.

"I spend a lot of time cleaning out files so I can make room for not a lot of content to be honest with you," Luczo observed. "I think are there some users that can operate in that environment and be happy... but I think as Seagate introduced a hybrid drive last quarter, you get basically the features and function of SSD at more like disk drive cost and capacity.

"I can tell you that my SSD drive takes about 25 to 30 seconds to boot now versus the 12 seconds when I bought it," he continued, "and [while] that’s just an issue more related to OS than it is specifically to the technology,... with the hybrid there [are] things that you can do [to] alleviate [it]... so your boot times are actually as compelling one and two, three and four years down the road."

Summarising, Luczo maintained that, if the question is whether massive SSD adoption is where mainstream notebook computing is going, he doesn't think so. On whether Apple will be successful with the new MacBook Air models, he would say absolutely affirmative, and that, "the more that people do creative things with computers and devices we're all for and Steve [Jobs is] certainly at the forefront of that."

So is significantly diminished speed performance and capacity an issue that someone mulling the purchase of an new MacBook Air or other SSD-equipped laptop or SSD upgrade should be concerned about?

Electronista says probably not, calling Luczo's statements, "Somewhat misleading", since in their estimation, the issue has mostly been solved on SSDs, at least with Windows, although not yet officially for Mac OS X. In a June, 2010 article, Electronista, citing AnandTech, notes that a technology called TRIM is key to the future market advance of SSDs, allowing as it does an operating system to optimise a solid-state drive in which blocks of data no longer considered in use can be wiped internally.

According to Wikipedia, "TRIM enables the SSD to handle garbage collection overhead, that would otherwise significantly slow down future write operations to the involved blocks, in advance." It explains that: "NAND flash memory cells can only be directly written to when they are empty. If they are considered to contain data, the contents first need to be erased before a write operation can be performed reliably. In SSDs, a write operation can be done on the page-level, but due to hardware limitations, erase commands always affect entire blocks.

"As a result, writing data to SSD media is very fast as long as empty pages can be used, but slows down considerably once previously written pages need to be overwritten. Since an erase of the cells in the page is needed before it can be written again, but only entire blocks can be erased, an overwrite will initiate a read-erase-modify-write cycle."

Electronista notes that Windows 7 and Windows Server 2008 support TRIM, but in June when the article was published, Apple hadn't built native TRIM support into OS X and thus Apple systems have derived less benefit from faster SSDs compared with Windows PCs.

My guess is that if at least some support for TRIM has not already quietly been added to OS X 10.6 Snow Leopard in a fractional version or security update, it should surely be incorporated in the forthcoming Mac OS X 10.7 Lion that Apple will release next summer.

As for Steve Luczo's contention that hybrid hard drives like his company's Momentus XT, would be a better alternative, offering what he claims to be basically the features and function of SSD at more like HDD cost and capacity, since they use flash memory more as a cache than as the main storage medium, as yet there is no indication of any major stampede toward hybrid drives in the laptop industry or aftermarket. Their relative bulk would also rule them out as an alternative solution for extremely thin laptops like the MacBook Air.

Late last week, Xbitlabs's Anton Shilov cited Western Digital CEO John Coyne's comments during a conference call with financial analysts. "We believe that the solid-state solutions are not competitive in the mainstream PC market, whether laptop or desktop, the economics just do not work out. Where the storage element is constrained by form-factor rather than on high price point devices, solid state is an appropriate solution," he said. Ergo, devices like the MacBook Air.

However, Coyne affirmed that while WD's own solid-state drive business was struggling, it will continue to hedge its bets with ongoing SSD development.

Forbes' Matt Schifrin cites Paul McWilliams, technologist and editor of Next Inning Technology Research, also noting that SSDs have a "wear-out" factor, which is a finite number of times that a single bit can be written and that number, when compared to HDD bit level endurance, is tiny. He adds that algorithms like TRIM can be used to detect the event and distribute writes so that a particular bit doesn't get over-worked, but that it's still an issue.

What we can take away from all of this is that prospective buyers of SSD-equipped laptops or SSD upgrades should be mindful that the SSD is immature technology compared with the venerable HDD, and proceed accordingly in anticipation that, as yet, an SSD's service lifespan may be considerably shorter than that of a traditional HDD.

Also that performance gains when the SSD is fresh may diminish with use, especially with computers running OS X until TRIM technology is fully integrated.