Enlarge / This isn't Western Digital's first 20TB drive—but it is the first shipping drive to achieve that density without the use of Shingled Magnetic Recording (SMR) technology. (credit: Western Digital)

At Western Digital's HDD Reimagine Event yesterday, the company introduced its newest hard drive architecture—a hybrid spinning rust/NAND flash design it calls OptiNAND. But as WD President of Technology and Strategy Dr. Siva Sivaram told Ars in an interview, OptiNAND bears almost no resemblance to the much-maligned hybrid SSHD drives first introduced in 2011 and 2012.

Instead of promising SSD-like speeds via caching of customer data, OptiNAND offers increased areal density by removing firmware-accessible metadata from the disk itself and storing it on NAND instead.

20TB per disk without SMR

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  Like last year's 20TB SMR drives, the OptiNAND drives employ EAMR in the form of an additional current to the main pole of the write head. [credit: Western Digital ]

The most tangible milestone achieved by Western Digital's newly announced architecture is a nine-platter, 20TB drive that does not require Shingled Magnetic Recording ( SMR ) techniques. The new disk uses a subset of Western Digital's EAMR technology, which has been rebranded ePMR—presumably to emphasize that it's not SMR, which has severe performance and usability implications for many common workloads.

Enlarge / You can't see the part number which distinguishes the newer, slower drive from the older, faster one on the box—you need to check the PN field in the top center of the label on the drive itself. (credit: Jim Salter)

Recently, major SSD vendors Crucial and Western Digital have both been caught swapping out TLC NAND in their consumer SSDs for cheaper but much lower-performance, lower-endurance QLC NAND. Samsung appears to be joining them in the part-swapping corner of shame today, thanks to Chinese Youtuber 潮玩客, who documented a new version of the Samsung 970 Evo Plus using an inferior drive controller.

Although the consumer-facing model number of the drives did not change—it was a 970 Evo Plus last year, and it's still a 970 Evo Plus now—the manufacturer part number did. Unfortunately, the manufacturer part number isn't visible on the box the SSD comes in—as far as we've been able to determine, it's only shown on a small label on the drive itself.

Falling off the write cliff

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  This CrystalDiskMark test makes the newer, inferior drive look faster than the original in most tests—but notice the very small 1GiB test size. This test isn't escaping the SLC write cache! [credit: 潮玩客 ]

We tested the 970 Evo Plus (alongside the 980, and the older 970 Pro) in March, clocking it at write speeds of 1,600+ MiB/sec on 1MiB workloads. Our benchmarking was done with he old version, part number MZVLB1T0HBLR. The newer version—part number MZVL21T0HBLU—is considerably slower. According to 潮玩客's test results, the newer version only manages 830MiB/sec—half the performance of the original.

Enlarge / Newer versions of Western Digital's WD Blue SN550 may perform worse than older ones. (credit: Western Digital )

Western Digital's WD Blue SN550 budget SSD is a well-reviewed, popular NVMe device that has regularly shown up on various sites' "best SSD" lists since it was released at the tail-end of 2019. The drive uses a four-lane PCI Express 3.0 interface and was novel for being able to perform better than SATA SSDs for about the same amount of money.

But that may be changing, thanks to quiet behind-the-scenes component changes: Chinese site Expreview (via Tom's Hardware and ExtremeTech ) says that a newer version of the drive manufactured in July 2021 was writing data at speeds of about 390MB per second after the drive's cache had filled up. According to Expreview, that's about half the speed of older versions of the SN550; Tom's Hardware measured speeds of about 610MB per second during a sustained write test on the original SN550, so the exact amount of performance degradation may vary. Because both the old and new versions of the SN550 use the same SSD controller, it seems likely that the slowdown is being caused by inferior NAND flash.

Modern SSDs typically pair a large amount of slower NAND flash (for capacity) and a smaller cache of faster flash memory (for the peak speeds advertised on the box). Depending on the SSD, this cache memory is designed to sustain anywhere between a few gigabytes' and a few dozen gigabytes' worth of writes before it has to fall back on the slower flash. Most of the time, you'll never notice the drive slowing down, because you're not going to fill the cache up all the way by using your computer for basic browsing, office work, or even photo editing.

Enlarge (credit: Seagate )

Earlier this month, Seagate announced an 18TB entry in its Ironwolf Pro lineup. Western Digital answered Wednesday morning with 18TB versions of its Red Pro and Purple consumer-targeted lines. The new 18TB Red Pro and Purple drives follow the company's first 18TB CMR drive, a Gold released in mid-July.

Both NAS (Network Attached Storage) drives—Seagate's Ironwolf Pro and Western Digital's Red Pro—are CMR drives and not the more performance-problematic SMR technology. Western Digital's announcement of the 18TB Purple did not mention either SMR or CMR at all, which we must assume means it is an SMR drive.

Seagate's 18TB Ironwolf Pro is available for ordering at select retailers now for $580 retail , but actual stock isn't expected until mid-October. Western 18TB Gold drives are available now for $593 ; the 18TB Red Pro and Purple drives are expected sometime in October but no prices have been announced yet.