they were selling wd red (pro?) drives with smr tech, which is known to be disastrous for disk arrays because both traditional raid and zfs tends to throw them out. the reason for that is when you are filling it up, especially when you do it quickly, it won't be able to process your writes after some time, and write operations will take a very long time, because the disk needs to rearrange its data before writing more. but raid solutions just see that the drive is not responding to the write command for a long time, and they think that's because the drive is bad.

it was a few years ago, but it was a shitfest because they didn't disclose it, and people were expecting that nas drives will work fine in their nas.