End-Of-Life Testing And Conclusion
Low-Density Parity Check (LDPC) is an advanced Error Correction and Control (ECC) algorithm used to extend NAND life. The technology first appeared in consumer SSDs with the introduction of 3-bit per cell (TLC) planar NAND, but now it also appears in some 2-bit per cell (MLC) 3D NAND products. LDPC is used in many different applications, such as satellite transmissions. In SSDs, the technology is roughly three times more powerful than the legacy BCH ECC algorithms that it replaced.
In a very simplified form, a modern SSD will use low-latency hard decision decoding first to recover a failed cell. If that fails, the SSD will shift to soft decision decoding, which requires more processing power. Soft decision decoding retrieves additional data from the failed cell, and surrounding cells, to recover the data. The miss with hard coding, and the resulting retry with soft decoding, adds increased latency to the read operation.
End-Of-Life Performance Testing
The Intel 600p is the first LDPC-enabled SSD we've pushed to the point of failure. Soft decision error correction can occur at any point, but it becomes more common during the latter phases of the flash's life. We decided to test the drive after the heavy wear to see if we could spot any performance variation due to an increased number of soft decision error corrections. With 10% life remaining, we ran a few tests to observe any latency changes and compare the results to our first tests. We couldn't push the degraded drive through our full test suite for fear of it dying in the middle, so we ran an abbreviated test session.
Four Corners Test
We didn't observe any significant performance changes in the synthetic tests. These are "quick hit" tests that we designed to measure burst performance. The Intel 600p is bursty in nature because it uses an inconsistent SLC buffer. With only a little time to stress the drive, we factored in the bursty workload during the degraded drive test to get an accurate measurement.
Real-World Software Testing
Our notebook battery life test using the Lenovo Y700-17 and BAPCo MobileMark 2014.5 did reveal a few slight differences. This test lasts over five hours, runs on real software with the device under test as the operating system disk, and is a true representation of your computer workload over an average workday.
We chose the test for two reasons. It's a real test with real software, but it also measures both performance and power. The soft decode process after a hard decode "miss" will increase power consumption momentarily. A hard decode miss will also decrease performance if it happens enough during our five-hour test.
We observed a nine-minute battery life decrease and a 142-point performance decrease. It's not a massive shift in performance, but it is enough to measure.
Like its other SSDs, Intel built the 600p with reliability in mind. Intel prides itself on very low return numbers, and at one point, it led the industry. That may still be true today, but we don't have the data to say one way or the other. Intel is one of the only companies that will lock the SSD before allowing the user to get into a dangerous state where data loss can occur.
Reputable endurance tests from media outlets show that some SSD manufacturers will allow you to write massive amounts of data beyond the endurance threshold--sometimes into the low petabyte range. However, the testers don't follow JEDEC testing standards and usually fail to factor in data retention during extended power-off periods. Consumer SSDs don't just have to keep writing data to meet JEDEC's requirements; they also have to retain the data for a period of time without power.
We think Intel is very aggressive with the amount of data written before moving into a read-only state. That is likely why we didn't see any latency in our synthetic tests even with only 10% of SSD life left. Our test with a lighter workload but over a larger LBA range and a longer time did show some performance degradation, but not enough to where we can point a finger and accurately identify it as LDPC latency.
The Intel 600p is a low-cost and reliable SSD, and for most users that is good enough. The chart above shows the top 30 consumer SSDs in a new test released by BAPCo. The company designed this subtest of SYSmark 2014 SE to show how responsive the storage subsystem is. In the future, we will examine the full test and how it calculates the score. The numbers come from a true client workload with real software running on a dedicated platform. The numbers represent a value over a base system with the reference being 1000. BAPCo scored the reference value with a Samsung OEM SSD that is closely related to the 750 EVO 250GB.
The Intel 600p 512GB is faster than every SATA product we've tested, including premium models like the SanDisk Extreme Pro, Samsung 850 Pro and Samsung 850 EVO. There are SSDs that are more responsive, but none match the 600p’s low price point. A few NVMe SSDs perform better, but only cost a few dollars more and deliver higher endurance, as well.
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