How it works
Inside, platters with a magnetic coating spin. A read/write head floats above the surface at a distance of a few nanometres and writes or reads magnetic regions. That is why a drive dislikes shocks while running.
HDD versus SSD
An SSD is faster, quieter and tougher. A hard disk is still much cheaper per terabyte, so it is used in NAS boxes, data centres and for backups.
What to watch when buying
- CMR vs SMR: SMR drives write overlapping tracks and can be very slow when a RAID rebuilds. Choose CMR for a NAS.
- NAS drives (such as Seagate IronWolf and WD Red Plus) are built for 24/7 operation.
- No drive is a backup. Every drive fails one day. See Backups and the 3-2-1 rule.