Intel SSD 660p 2TB Review: a QLC Bargain (Update)

12/6/2019 Update: We've updated this article with new testing for the 2TB 660p, as well as tweaked parts of the review to reflect current pricing.

When the Intel SSD 660p NVMe launched in summer 2018, it marked the arrival of the first consumer drive with QLC (quad-level cell) flash. Since then, the technology has appeared in a number of other SSDs as storage prices have dropped like a rock. At the same time, the Intel SSD 660p has become one of the best bargains in tech. With near-constant sales, you can often find the 660p selling for as little as $80 (£80) for a 1TB drive, though the 2TB models often go on sale for under $200 (£152).

One of the best SSDs you can get due to its mix of price and performance, the SSD 660p communicates over a fast PCIe 3.0 x4 and delivers up to 1.8 GB/s of throughput. It also offers surprisingly good performance in random workloads. If that wasn’t enough, the 660P comes with a five-year warranty.

We put the Intel SSD 660p 1TB capacity to the test and found that it offers a surprising amount of performance given its low price point. If your workload trends towards mundane daily tasks, like content consumption, office work, and web browsing, the 660p is a great solution with plenty of performance and endurance for most users. That said, if you like this SSD but wish it had more endurance, keep an eye out for the 660p's recently announced successor, the Intel SSD 665p, which promises slightly faster performance, and a 50% rated endurance bump.

While QLC sounds too good to be true, it’s not. Intel has a strong track record for developing new and innovative storage technology. The company was the first to bring NVMe SSDs to market four years ago with the Intel SSD 750 series, and it also developed the exotic 3D XPoint memory that it uses in the Optane products.

Intel’s 64-layer 3D QLC flash technology dramatically boosts flash storage capacity. MLC flash stores two bits per cell and TLC flash stores three, but QLC crams four bits into each cell. The 33% increase in density ultimately equates to more storage capacity for less money. Intel's QLC flash enables up to one 1-terabit (125GB) of storage capacity in a single die. SSD vendors can pack up to 16 die into a single package, which means QLC enables up to 2TB per package.

Just like Intel's other flash technology, QLC flash leverages the tried-and-true vertical floating gate flash cell design. Competing flash from other foundries use charge trap designs.

High-capacity and inexpensive flash is music to everyone’s ears, but QLC has an Achilles heel. Well, two. QLC NAND has lower write performance and less endurance than MLC or TLC flash because it stores 16 different charge levels per cell to represent four bits of data. Due to the physical characteristics of flash, it's a challenge to store and modify 16 charge levels at the nanometer scale, especially as the flash ages. Cell-to-cell interference complicates the task. Intel claims the 3D floating gate design helps isolate the cells to reduce interference. In either case, sophisticated error correction algorithms, such as LDPC, are a key ingredient to boosting endurance. 

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Intel sidesteps many of the performance challenges associated with QLC flash by tweaking the firmware and using intelligent idle time performance adjustments. Intel's Intelligent Dynamic SLC-Caching, which uses a pool of fast SLC flash to boost performance for incoming write data, takes a two-step approach.

First, the 660p has a static SLC cache that is 6GB, 12GB, or 24GB, depending upon SSD capacity. The static cache capacity never changes, but the SSD has a larger dynamic SLC cache pool that boosts performance further. The dynamic cache capacity adjusts bi-directionally based upon the amount of data stored on the SSD. In other words, the cache shrinks as you fill up the drive but expands as you delete items. Higher-capacity 660p's have larger dynamic SLC caches, as outlined in the chart above.

The SLC pool flushes to the QLC flash during idle periods, but Intel has a new on-demand performance boost option if you need your SLC performance back right away after bombarding the drive with writes. The feature allows you to flush the SLC cache to the QLC flash manually. Intel added this feature to its SSD optimizer in SSD Toolbox version 3.5.3.

Specifications

Intel rates the 1TB and 2TB models for 1.8 GB/s of sequential read/write throughput, but the 512GB model steps back to 1.5/1 GB/s read/write. The write specification is based on the 660p’s dynamic SLC cache, however, so the drive could slow during extended write workloads when the workload spills over to the native QLC flash. We simulated the condition with a worst-case test, and the 1TB model fell to ~100 MB/s after writing 130GB of data from an empty state. Given the size of the 660p's SLC caches, you will likely never encounter this condition.

The 2TB Intel SSD 660p provides up to 220,000/200,000 random read/write IOPS, but the smaller models have slower random read performance. Our 1TB model provides up to 150,00 random read IOPS.

Intel rates the 660p’s endurance as 100TBW per 512GB, or just over 0.1 drive write per day over the five-year warranty period. The 660p’s endurance is (on average) 33 percent lower than other PCIe based SSDs and roughly half that of budget SATA SSDs. Two hundred terabytes of write endurance might not seem like a lot, but Intel says it should be enough for most light, bursty workloads in desktop PCs. If your workloads are more intense, like frequent large file transfers, video processing, or workstation-class applications, other more endurant SSDs are a better choice.

The 660p features AES-256 encryption with Pyrite 1.0 and 2.0 support, which is a nice addition for the security conscious.

A Closer Look

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The Intel SSD 660p is a PCIe 3.0 x4 SSD that comes in an M.2 2280 single-sided form factor. It communicates with the host system via the NVMe 1.3 protocol and weighs in at just 5.5g. There are two 512GB 64-layer QLC flash emplacements on the PCB of the 1TB capacity.

The 660p comes with SMI's 2263 SSD controller and Intel's proprietary firmware. A single 256MB NANYA DDR3L DRAM chip flanks the controller. Most SSDs have a 1MB of DRAM to 1GB of flash ratio, but the Intel 660p has 1MB of DRAM per 4GB of flash. Intel could be compressing the LBA map or might have implemented the Host Memory Buffer (HMB) feature, which stores a portion of the LBA map in system memory.

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