SSD vs HDD for a NAS
When to use hard drives vs SSDs in a NAS - bulk storage, cache, and all-flash setups explained.
For most NAS builds the honest answer is "both, doing different jobs". Hard drives still win bulk storage on price - you're looking at roughly $12-20 per terabyte for a NAS HDD versus $60+ for SSD. SSDs earn their slot as cache or in an all-flash performance box.
HDDs for bulk storage
The main pool - media, backups, photos, archives - belongs on CMR NAS hard drives. They're a fraction of the per-terabyte cost of flash and plenty fast for the large sequential reads and writes a NAS actually does most of the time. Here, capacity is the spec that matters, and spinning disks deliver it cheaply.
SSDs for cache or metadata
Most NAS platforms let you bolt on SSDs as a read/write cache (on ZFS, that's L2ARC, SLOG, or a metadata special vdev). A modest SSD cache makes a HDD-backed pool feel far snappier for the files you touch often and for small random I/O, without paying the all-flash premium across your whole library. Don't oversize it - a cache only helps the working set, not cold archive data.
All-flash NAS: when it's worth it
Go all-SSD when latency is the point: editing video off the NAS, hosting databases or VM disks, or a dozen people hammering small files at once. You pay several times the per-terabyte cost, so reserve it for the workloads that genuinely feel the difference.
Rule of thumb
- Bulk capacity, best value: HDD (CMR, NAS-rated).
- Cheap speed boost on a HDD pool: add an SSD cache.
- Latency-critical work, budget aside: all-flash.
For the storage half, start with the drive list and the storage planner, and confirm any hard drive is CMR before it goes in an array.