Thanks for following up with this, with your experiences using Intel desktop RAID 1 and (presumably) NTFS.

For lurkers there's a comprehensive article at https://www.servethehome.com/wd-red-smr-vs-cmr-tested-avoid-red-smr/ . It's a good data point that you're seeing CMR performance as 3x SMR in your resilvering.

From what I gather SMR drives have a CMR cache, so for small, intermittent writes a user might not notice the difference. However performance clearly suffers if this cache is overwhelmed, either by large conventional copy operations, or a worst-case complete resilvering.

The second page of the article shows a test resilvering a RAID array under ZFS/Linux (RAIDZ) going from 17 hours (CMR) to over 230 hours (SMR), a factor of more than 10. As it points out, having a degraded array vulnerable for over a week is not acceptable. It's interesting that you saw "only" a factor of 3.

As for the class action, I gather WD was specifically recommending SMR drives for NAS usage but with other vendors it wasn't so cut and dried, so maybe not as simple to bring a suit (?)

>Thanks to Al Doman in Vancouver who turned me onto the difference between SMR (slow) and CMR (best) harddrives and how the SMRs don't perform well in a RAID situation.
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>I had a pair of 8 year old Seagate drives that were CMR in my RAID 1 configuration on my Dell XPS Desktop (2012) and one of the Seagates failed and I decided to replace both drives as a precaution. Well, Seagate was slip streaming SMR drives and I ended up with two 7200 RPM SATA 3 drives 2 TB. It took 15 hours to resilver the SMR drives one at a time as I migrated off the one working CMR drive.
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>So, I was having a hard time convincing myself to buy two new CMR drives when I decided I'm going to put back into service the working Seagate CMR drive and buy one new WD Red Pro (CMR 7200 RPM Sata 3 2TB) drive which cost $120. I just couldn't stomach buying two of those and then throwing out the 2 SMR drives at $60 each. My little project would be a $360 deal. So, instead I'm just out $120 for one new WD drive.
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>Anyway, I unplugged one of the SMR drives and plugged in the old Seagate CMR drive and flipped a few switches in the Intel RAID application and in only 5 hours the Seagate was restored instead of 15 hours.
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>I've added the new WD Red Pro and it's rebuilding now and I'm hoping for another 5 hours and I'll be done with this project and hopefully I won't be as worried.
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>Again, thanks for the heads up. I'm only hoping there's a class action lawsuit against Seagate like there was with Western Digital about these SMR drives.