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MK4001GRZB : Great Endurance, Fast Reads, Slower Writes

Toshiba's $7000+ 400 GB SSD: SAS 6Gb/s, SLC Flash, And Big Endurance

The cadre of IT managers who make purchasing decisions for big enterprises don't just read reviews and buy pallets of storage devices. Rather, they spend weeks and months with new technologies in isolated servers, testing their mettle before deploying into production. In many performance-sensitive workloads, SSDs make a lot of sense. They can even save money when they replace a much larger quantity of disk drives. But reliability is of the utmost importance and, by extension, endurance receives attention as well.

As a result, it's difficult to render final judgement on an enterprise-class SSDs. Performance isn't the headliner that it is in desktop environments. Rather, it shares the spotlight with data security, and that's a very difficult variable to quantify.

We can determine performance over the course of a weekend (even taking steady states into account). If the only thing you care about is raw throughput, you could conclude that Toshiba's MK4001GRZB delivers excellent read speed, but is generally matched by desktop-class drives like Intel's SSD 520 that cost a lot less and facilitate better efficiency. The MK4001GRZB sells for more than $7000, while a 480 GB SSD 520 is available under $1000. A 200 GB P300 goes for somewhere around $2000, which can't stand up to the Intel drive, but it also employs SLC NAND, too.

Reliability is the real challenge. Statistically, a handful of reviews is insufficient for crowning one company or another the best for keeping data secure. To really gauge reliability, you'd need to watch the failure rate of a large population of SSDs subjected to the same workload. Why? Because solid-state storage changes its behavior based on activity, which cannot be said for hard drives. Right now, vendors only seem willing to cite the return rates from distributors, which generally involve fairly small sample sizes. Invariably, it'll take more time and a study like Google's own independent analysis of failure trends to shed more light on how SSDs compare.

Endurance is related to reliability, but certainly not the only (or most important, even) determinant of it. It's possible to test and estimate the rated longevity of an SSD using SMART (Self-Monitoring, Analysis and Reporting Technology) tables and a bit of math. Unfortunately, it is a very time-consuming process. In order to give you an idea of what it took for us to present endurance figures for Toshiba's drive, we had to write to the MK4001GRZB for 41 days, 24 hours a day, to get the MWI to drop 1%. In the process, we wrote approximately 900 TB worth of data. And that figure only applies to a purely sequential workload. Estimating endurance for random access would require a separate test, as write amplification is higher. We're not sure how much longer testing would have taken, but it could have been as long as three or four months.

As a result, our conclusions are and will always be admittedly less complete than a review conducted over the course of months or even years. But that's the trade-off for also publishing something in a timely manner. This could have been a great candidate for a long-term story where we put the rubber to the road and go ahead with calculating random I/O endurance as well. Alas, with a $7000+ price tag, it's understandable that Toshiba wanted to get the drive back sooner than later.

At the end of the day, based on our testing, we can say that Toshiba's MK4001GRZB offers very fast reads, slower write performance, and amazing endurance in sequential workloads. The last point can't be understated. In an environment pushing sequential writes all day, every day, it'd take more than 11 years to use up the 400 GB model's rated P/E cycles. That's well beyond Toshiba's five-year warranty. And so, when it comes to enterprise storage, the MK4001GRZB  shows us why SLC flash is still top-of-the-line. 

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