In the beginning, server SSDs relied exclusively on SLC NAND with one bit per cell. MLC-based drives with two bits per cell have become more popular in recent years, though. These drives offer sufficient performance and endurance for many enterprise tasks, minus the hefty price premium associated with SLC NAND. Now, Samsung has gone one step further with a new PM853T server SSD based on TLC flash with three bits per cell.
The PM853T is already in mass production, according to the official press release, and Samsung is quite bullish about its chances. The company "expects the adoption of 3-bit SSDs in data centers to advance rapidly in replacing the 2-bit SSD market."
According to the press release, the PM853T is available in 240, 480, and 960GB capacities. It's rated for 530MB/s sequential reads and 420MB/s sequential writes. On the random I/O front, the drive is said to be good for 90,000 read IOps and 14,000 write IOps. That random write figure is a little on the low side, likely due to the slower write performance associated with TLC NAND.
The flash comes from the "10-nanometer-class" generation, Samsung says, and it's probably similar to the 19-nm TLC NAND found in the 840 EVO consumer drive. Samsung makes the NAND itself, and it also has in-house controller technology. The PM853T's controller chip may be similar to the one used in the EVO, though there's no mention of the consumer drive's fancy write caching mojo.
Obviously, endurance is a big concern for TLC NAND. The press release is devoid of details, so we've asked Samsung for information on the PM853T's endurance specification. We'll update this story when we get a response.
The TLC-based Samsung 840 Series drive in our ongoing SSD endurance experiment has survived nearly a petabyte of writes thus far. That's an impressive total, though the drive did encounter some problems along the way. I'm curious to see if server admins trust TLC NAND enough to deploy it in the datacenters Samsung is targeting with the PM853T. Surely, there are some enterprise workloads with relatively low endurance requirements.
Update: Samsung has provided us with endurance ratings for the PM853T. With a "random 4K write workload," the 240GB model is supposed to be good for 165TB of total writes. The 480GB drive is rated for 330TB, while the 960GB is specced at 665TB.
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