SSD

SSDs store data in NAND flash memory — the same technology in USB drives and memory cards, but engineered for reliability and endurance. The absence of moving parts means access times of microseconds rather than milliseconds, and no mechanical failure modes.

SSD interfaces

SATA SSD — uses the same interface as HDDs. A drop-in replacement for a spinning drive, with SSD random I/O performance. Maxes out at ~550MB/s sequential read due to the SATA interface ceiling. Adequate for general computing; limited for high-performance storage.

NVMe SSD — connects via PCIe directly to the CPU, with no SATA bottleneck. 3-7GB/s sequential read on consumer drives, higher on enterprise models. The right choice for OS drives, VM storage, and any application with significant I/O demands.

SSD endurance

Flash cells wear out — each write cycle degrades them slightly. Enterprise SSDs have higher endurance ratings (measured in TBW — terabytes written) and may use more durable SLC or MLC NAND rather than the TLC or QLC found in consumer drives. For NAS arrays with write-intensive workloads (caching, frequent backups), specifying the right endurance tier matters.

Caching in storage systems

Synology and similar NAS platforms can use SSDs as a read/write cache in front of an HDD array — the SSDs absorb the random I/O workload while the HDDs handle bulk sequential storage. This can dramatically improve performance for file server and small database use cases at lower cost than all-SSD storage.