Storage media types

April 23, 2026 · in Intro to SAN and NAS Storage (Neil Anderson)

HDD vs SSD

HDD is a spinning platter. SSD has no moving parts and is faster; enterprise folks say “flash.”

SATA vs SAS

Home PCs run SATA. Servers and arrays run SAS (Serial Attached SCSI), with higher performance in server workloads.

SAS is an architecture: SAS shelves, SAS cables to the controllers, SAS drive bays. It’s backward compatible: a SAS bay accepts SAS SSD, SAS HDD, SATA SSD, or SATA HDD. Not the other way around.

Picking a drive

SSD: highest performance, lower capacity, highest cost per GB. Performance tiers.
SAS HDD: middle on all three. Balanced workloads.
SATA HDD: lowest performance, biggest capacity, lowest cost per GB. Bulk capacity.

Legacy interfaces you’ll only see in old gear: parallel SCSI and FC-AL. Incompatible connectors, dead tech.

NVMe and SCM

SAS and SATA were designed around spinning disk speeds; with SSDs the controller-to-disk link becomes the bottleneck. NVMe rides the PCIe bus instead, and it’s not physically compatible with SAS/SATA bays.

NVMe over the network: NVMe over Fabrics.

Storage Class Memory is persistent storage in memory slots (NVRAM instead of DRAM) that survives power loss. Intel 3D XPoint was the early example.

All flash vs hybrid

SSD prices keep falling, so all-flash arrays are now mainstream. Hybrid arrays mix flash for speed with HDD for cheap capacity.