Results: Write Endurance
We typically spend a lot of time looking at write endurance when we review enterprise-class SSDs. Write endurance is one of the major differentiators separating enterprise and client-oriented drives, after all. As MLC-based storage continues pushing its way into spaces previously filled by SLC NAND, we have to keep a close eye on this difficult-to-benchmark, but still very important variable involved in evaluating solid-state storage.
The rise of read-focused enterprise drives makes the testing we're doing even more important, since you really want to know what writes will do to storage hardware designed for read-heavy workloads. Naturally, we have to appreciate the companies that treat write endurance as a first-class specification, and much of the credit for that goes to JEDEC for its JESD218A write endurance testing standard. Instead of issuing vague ratings, we now see most companies specifying their drives to JESD218A, which uses the JESD219A enterprise workload to quantify endurance. This closely matches the types of workloads we use in our Enterprise Workload Performance tests, employing sequential write patterns and large block sizes. The result is minimal write amplification and wear leveling, yielding a better indication of actual P/E cycles for the NAND.
|Endurance RatingSequential Workload, QD=1, 8 MB||Intel SSD DC S3500||Seagate 600 Pro||Intel SSD DC S3700|
|NAND Type||Intel 20 nm MLC||Toshiba 19 nm MLC||Intel 25 nm HET-MLC|
|RAW NAND Capacity||528 GB||256 GB||264 GB|
|IDEMA Capacity (User Accessible)||480 GB||200 GB||200 GB|
|P/E Cycles Observed (IDEMA)||3,326||6,245||36,343|
|P/E Cycles Observed (RAW)||3,024||4,879||27,532|
|Host Writes per 1% of MWI||15.97 TB||12.49 TB||72.69 TB|
As we saw in Seagate 600 Pro-Series 200 GB SSD Review: For The Enterprise, read-focused SSDs are ill suited for write-intensive applications. Compared to the SSD DC S3700, you get roughly one-tenth of the endurance for half of the price. We don't consider that a good deal. Fortunately, you don't buy this drive for its great write endurance. You simply want to know what it'd do if you were to tax it with writes.
The bad news is that, up against Seagate's 600 Pro, write endurance looks even worse for the SSD DC S3500. Seagate's drive holds a commanding 60% lead in P/E cycles observed.
Now, we'll step back and consider what the two companies say about endurance. They both present specifications using the JESD218A standard, and they both sell 480 GB SSD. Intel states its write endurance at 275 terabytes written (TBW), while Seagate states 350 TBW. That's not the 60% we observed, but it's still a large 27% difference.
It's more difficult to compare write endurance between capacities. With Intel, the odd NAND configurations change over-provisioning at each capacity point. This means that the 800 GB model has exactly twice the endurance rating as the 400 GB version, but the 480 GB drive is slightly less than double that of the 240 GB SSD. Seagate, meanwhile, uses a complex endurance rating system based on the amount of factory over-provisioning. The 200 GB 600 Pro that we tested is rated at 520 TBW, while the 240 GB version, with the exact same amount of NAND, is rated at only 134 TBW. Even this ratio of TBW varies across capacities, from 3x to nearly 10x.
What does all of this information tell us about write endurance? Like all tests that involve random, small-block workloads (JESD218A), write endurance is heavily affected by over-provisioning. This is one of the reasons we test with large-block sequential workloads. The low write amplification helps us see through any configuration FUD. We weren't able to put that theory to the test by over-provisioning the SSD DC S3500 to 600 Pro levels in this story, but expect that analysis in the near future.
Bringing it all back to Intel's SSD DC S3500, by all measurable and stated results, Seagate's 600 Pro provides higher write endurance. With that in mind, how important is write endurance on a drive that was not made for write-intensive applications? Now more than ever, this SSD encourages you to be educated about the workloads you apply to it, else you spend a lot of time and money on replacements.