In 07/2015 and 11/2015 I bought 8 WD Red 6 TB each. All were WD60EFRX, i.e. CMR types or today's "Plus". At that time, there was no SMR scam from WD and no "Plus" designations. Since then, they have all been in continuous operation (7 HD each as RAID6 + 1 HD as hot spare in 8-bay NAS).

1 CMR HD failure with bad sectors replaced 09/2019 with a WD60EFAX (SMR). Since then runs without problems in the RAID of a QNAP TS-853 PRO 8GB (not as hot spare). However, I have not yet had a RAID rebuild with this HD.

1 possible CMR HD failure with bad sectors now 11/2020. I/O Error, Bad Sector Scan currently running.

CMR and SMR HD's are easily distinguishable in WD Red and WD60 by the model designation: EFRX = CMR / EFAX = SMR, or missing R in the second last position.

Whether SMR HDs lead to problems in a RAID rebuild depends very much on the NAS. According to QNAP, the newer WD Red SMR HDs were tested in the TS-853 PRO NAS and found to be good. Depending on the NAS model and manufacturer, please do your own research to find out if HDs are compatible or if there are restrictions/hints.

The failure frequency of the WD60EFRX corresponds to my experience with NAS HDs in seven other 4-bay NASes (the majority 4 TB HDs, presumably all CMR, no hot spares), some of which have been in continuous operation for much longer (periodically at least half of the time).(periodic NAS-to-NAS mirroring as a backup of important data - RAID6 mirroring may sound crazy, but my last data loss was in 1988 - since then I have maintained double or quadruple data redundancy as well as double hardware redundancy).

Desktop HDs fail much more often and enterprise HDs almost never.