Review on 🔒 Reliable Performance: Western Digital 4TB WD Red SMR NAS Internal Hard Drive - 5400 RPM, SATA 6 Gb/s, 256MB Cache, 3.5" - WD40EFAX by Devin Lee

Western Digital is replacing older CMR (Conventional Magnetic Recording) discs with lower SMR (Shingled Magnetic Recording) discs. SMR is a technology that allows them to provide higher storage densities by providing more TB capacity on the same number of platters - or fewer platters on the same TB (aka cheaper manufacturing). The problem is that SMR, in addition to higher capacity, comes with much lower random I/O performance than CMR drives offer. SMR drives also have problems removing them from arrays, if they work at all. If you look at the model number, the EFRX model is a faster CMR drive, while the EFAX models are SMR drives with very poor sequential write speeds. SMR drives also require more cache to help with slow write speeds.