Ars Technica did some detailed testing of these drives a couple weeks ago. See "We put Western Digital’s dreaded SMR Red drive to the test" [1]. They found that they won't work for ZFS but are actually OK in most NASes.

Here is their conclusion:

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We want to be very clear: we agree with Seagate's Greg Belloni, who stated on the company's behalf that they "do not recommend SMR for NAS applications." At absolute best, SMR disks underperform significantly in comparison to CMR disks; at their worst, they can fall flat on their face so badly that they may be mistakenly detected as failed hardware.

With that said, we can see why Western Digital believed, after what we assume was a considerable amount of laboratory testing, that their disks would be "OK" for typical NAS usage. Although obviously slower than their Ironwolf competitors, they performed adequately both for conventional RAID rebuilds and for typical day-to-day NAS file-sharing workloads.

We were genuinely impressed with how well the firmware adapted itself to most workloads—this is a clear example of RFC 1925 2.(3) in action, but the thrust does appear sufficient to the purpose. Unfortunately, it would appear that Western Digital did not test ZFS, which a substantial minority of their customer base depends upon.

These tests may not be great news for either the American or Canadian class-action lawsuits currently underway against Western Digital, but they aren't the end of the line for those lawsuits, either. Even in the best case, the SMR models of WD Red underperform their earlier, non-SMR counterparts substantially—and consumers were not given clear notice of the downgrade.

If the same firmware was being used to make substantially larger drives available to consumers than would otherwise be possible, and the limitations of those drives were adequately explained, we would probably be gushing over its utility and function. Unfortunately, Western Digital has so far only chosen to use it to cut manufacturing costs on small disks, without even passing the savings along to the consumer.

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That last paragraph may be key. It sounds like if these drives had been marketed a little different and priced a little different they could have been a good deal for many NAS users.

I wonder what the chances are that they were originally intended for just that, and something got mixed up or miscommunication between design and release?

[1] https://arstechnica.com/gadgets/2020/06/western-digitals-smr...