My EX4100 has 4 x 2TB discs WD20EFAX, configured for RAID-5. I just used my last spare unit when one of the running discs was ‘degraded’. I see that WD20EFA-units are not available anymore, I see for example 2TB units WD20EFPX.
Question: if next time one of my discs degrade, can I replace WD20EFAX with WD20PFAX? I would then have 3 x WD20EFAX combined with 1 x WD20EFPX; will my RAID-5 configuration still work in this case? If not, is there any other disc-type I can use in combination with my WD20EFAX to ensure my (so far) good working RAID-5 configuration?
Any drive the same size as the other drives should work.
The WD20EFAX, if I understand the specs correctly, is a WD Red 2TB 5400rpm SMR drive.
SMR drives (no matter the manufacturer) should be avoided for all applications and all use cases.
WD20PFAX WD Red Pro, 2tb 7200rpm CMR drive. It should work fine. 7200rpm is technically better than a 5400rpm, but I would challenge anyone to tell the difference in a NAS system with a 1gb network connection. CMR is what you want for most applications.
For my money, I would go with any 2tb, 5400rpm, CMR drive.
I’d also check whether the EX4100 is rebuilding cleanly before worrying about mixing models. In practice, RAID-5 doesn’t care if one drive is an EFAX and another is an EFPX as long as the replacement is at least the same usable capacity and the NAS accepts it.
The bigger concern is mixing recording technologies, because an SMR drive can dramatically slow rebuilds and increase stress on the remaining disks. Since you’re already replacing failed drives one at a time, I’d start migrating the array toward CMR drives rather than trying to find more EFAX units.
Just expect the rebuild to run at the pace of the slowest drive until the older disks are phased out, and keep a verified backup because RAID protects against a drive failure, not a bad rebuild or a second disk failing during recovery.
