Verdict

These two are closely matched CMR NAS drives of the same capacity - decide on price and warranty. Check the live $/TB above.

WD181KFGX WD181KRYZ
Capacity 18 TB 18 TB
Recording tech CMR CMR
RAID / NAS safe Yes Yes
Class NAS-Pro Enterprise
Spindle speed 7200 RPM 7200 RPM
Cache 512 MB 512 MB
Noise (idle) 20 dB 20 dB
Fill Helium Helium
Interface SATA SATA
Failure rate (AFR) - -
Price / TB $40.83 $34.45

Highlighted cells mark the stronger spec for a NAS build. Failure rates from Backblaze Drive Stats where available; $/TB shows once live prices are wired.