Best 4-Bay NAS in 2026

A 4-bay NAS is the upgrade that changes what network-attached storage can do for you. Where a 2-bay NAS in RAID 1 gives you mirrored storage with half your raw capacity available, four bays unlock RAID 5 — three drives of usable capacity with one drive's worth of parity protection — and RAID 6, which survives two simultaneous drive failures. Four bays also give you room to grow capacity by replacing drives one at a time over several years, without replacing the enclosure.

The 4-bay NAS market in 2026 spans a wide range of capability and price. The Synology DS923+ and QNAP TS-464 sit at the upper end of the mainstream tier with AMD Ryzen and Intel Celeron processors, PCIe expansion slots for 10GbE, and strong multi-service performance. The TerraMaster F4-424 and QNAP TS-462 offer solid value for users who prioritize hardware at the cost of some software ecosystem depth. This guide covers what actually matters when choosing between them.

Top 5 Four-Bay NAS Picks at a Glance

Our Picks in Detail

RAID 5 vs RAID 6 in a 4-Bay NAS: How Much Protection Do You Need?

RAID level selection is the first real decision a 4-bay NAS buyer needs to make, because it determines both how much usable storage you get and how much risk you carry during drive failures.

RAID 5 distributes parity across all drives in the array. With four drives, three drives' worth of capacity is usable and one drive's worth is dedicated to distributed parity. Four 8TB drives in RAID 5 yields approximately 24TB of usable storage. RAID 5 can survive any single simultaneous drive failure — while one drive is failed or being replaced, the array continues to operate in a degraded state, rebuilding onto the replacement once it is inserted.

The risk with RAID 5 lies in the rebuild process. Rebuilding a RAID 5 array after a drive failure on large modern drives — 12TB, 16TB, 20TB — takes 12 to 48 hours depending on drive speed, NAS CPU speed, and ongoing workload during the rebuild. During that entire rebuild window, the array has no parity protection. A second drive failure at any point during the rebuild destroys the entire array. With modern high-capacity drives, the probability of a second drive failure during a multi-day rebuild is not negligible.

RAID 6 uses two drives for parity rather than one, meaning the array can survive any two simultaneous drive failures. With four drives, two drives' worth of capacity is usable. Four 8TB drives in RAID 6 yields approximately 16TB of usable storage — a meaningful capacity reduction compared to RAID 5, but one that comes with significantly stronger protection during the most dangerous period: the rebuild window after a first failure.

For a 4-bay home NAS with drives up to 8TB, RAID 5 is a reasonable choice as long as you also maintain offsite backups of data you cannot afford to lose. For drives at 12TB and above, or for any business or prosumer use case where data loss is costly, RAID 6 is the safer default despite the capacity penalty. All five picks in this guide support both RAID 5 and RAID 6.

4-Bay NAS Capacity Planning: How Much Storage Can You Build?

Four bays give you meaningful headroom for large storage builds. The practical capacity range for a current 4-bay NAS spans from a modest 12TB usable (four 6TB drives in RAID 5) to approximately 60TB usable (four 20TB drives in RAID 5) — more than most home users will fill for several years.

A realistic starting configuration for a home media server or family backup NAS is four 8TB drives in RAID 5: 24TB usable, drives that cost roughly $120–$150 each. For a large photo and video library alongside full workstation backups for a family, 24TB is enough to last several years before an upgrade is needed. When capacity eventually runs short, Synology and QNAP both support online RAID expansion — replacing drives one at a time with larger ones and expanding the volume after all drives are upgraded, without losing data or taking the NAS offline.

For heavier use cases — 4K video editing storage, large Plex libraries with full-quality rips, continuous camera recording — four 16TB drives in RAID 5 yields approximately 48TB usable. At current drive prices, four 16TB IronWolf or WD Red Pro drives cost roughly $800–$1,000 for the set, on top of the NAS enclosure price. That is the practical ceiling for most home 4-bay builds and leaves ample room for years of data growth.

PCIe Expansion Slots: 10GbE and NVMe Cache in 4-Bay NAS

The Synology DS923+ and QNAP TS-464 both include PCIe 3.0 expansion slots — a feature that meaningfully expands what the NAS can do beyond its base configuration.

The most common PCIe upgrade is a 10GbE network card. On the Synology DS923+, the PCIe 3.0 x2 slot accepts Synology's E10G22-T1-Mini (single 10GbE RJ45 port) or E10G18-T1 card. This upgrades the NAS from dual 1GbE to 10GbE for approximately $120–$150, transforming file transfer speeds from the ~115 MB/s gigabit ceiling to the 800–1,000 MB/s range that modern SSDs and RAID arrays can sustain. QNAP's TS-464 PCIe slot accepts QNAP's QXG-10G1T card for a similar upgrade.

The second common PCIe use is NVMe SSD caching. Synology's M.2 SSD cache adapters allow adding one or two NVMe SSDs to the DS923+'s PCIe slot, using them as a read/write cache in front of the spinning hard drive array. For workloads with many small random read/write operations — databases, photo management apps, active Plex metadata — SSD caching measurably reduces latency. For large sequential workloads like video streaming, the benefit is less pronounced.

The Synology DS423+ and TerraMaster F4-424 lack PCIe expansion slots entirely. The DS423+ is a deliberate simplification — the same Synology software at a lower price, without the expandability of the DS923+. If 10GbE or NVMe cache is on your roadmap, the DS923+ is the correct Synology choice; the DS423+ is the right pick when you want the software quality without paying for expandability you will not use.

ECC vs Non-ECC RAM in a 4-Bay NAS: Does It Matter?

ECC (Error-Correcting Code) RAM is one of the least-discussed but most meaningful differentiators between prosumer and consumer NAS hardware. Standard DDR4 RAM stores data in memory cells that can occasionally flip a single bit due to cosmic ray interference or electrical noise — rare, but not negligible over months of continuous operation. A bit flip in memory that is subsequently written to disk can silently corrupt a file in a way that is not detected until the file is opened weeks or months later.

ECC RAM adds extra bits to each memory word and uses them to detect and correct single-bit errors before they propagate to storage. It is standard in enterprise servers for exactly this reason. Among mainstream 4-bay NAS devices, the Synology DS923+ is the standout: it uses ECC DDR4 SO-DIMMs and is the only unit in this comparison that offers hardware-level RAM error correction.

For a home NAS storing family photos and workstation backups, the practical risk from non-ECC RAM is low — bit errors are rare events, and modern file systems with checksumming (like Btrfs, which Synology uses) can detect corruption even if they cannot always correct it. For a prosumer or small-business NAS where data integrity is business-critical, the DS923+'s ECC support is a meaningful advantage that justifies its price premium over the DS423+.

The QNAP TS-464, TerraMaster F4-424, and QNAP TS-462 all use non-ECC DDR4, which is standard for their price tier and perfectly adequate for most home and light prosumer workloads.

4-Bay NAS for Plex, Photos, Backup, and Virtualization Simultaneously

One of the main reasons to choose a 4-bay NAS over a 2-bay unit is the ability to run multiple services concurrently without performance degradation. A 4-bay NAS handling Plex transcoding, a photo management app like Synology Photos or PhotoPrism, Time Machine backup from multiple Macs, and a Docker container or two simultaneously is a realistic and common configuration.

The QNAP TS-464 is the strongest performer for this multi-workload scenario among the picks in this guide. Its Intel Celeron N5105 supports Intel Quick Sync Video (QSV) hardware transcoding, which means Plex can transcode multiple streams without significantly loading the CPU — leaving headroom for backup agents, Docker containers, and file serving to run simultaneously. It also ships with 8GB of DDR4, which is enough for most multi-service configurations without a RAM upgrade.

The Synology DS923+ with its AMD Ryzen R1600 dual-core processor does not support hardware video transcoding natively (Synology limits transcoding licensing on NAS hardware), but its CPU performance and ECC RAM make it the better choice for virtualization, Docker-heavy setups, and workloads that prioritize CPU compute and memory integrity over transcoding throughput. Upgrading the DS923+ to 16GB or 32GB of ECC RAM is straightforward and meaningfully expands its multi-service capability.

For both units, the practical advice is to monitor RAM utilization after your first few weeks of use and upgrade if you consistently see memory above 80% utilization. RAM is the most common first bottleneck in multi-service NAS configurations — more so than CPU or drive throughput for the workloads typical home and prosumer users run.

Frequently Asked Questions

What is the usable capacity of a 4-bay NAS in RAID 5?

Three drives' worth of capacity. Four 8TB drives in RAID 5 gives approximately 24TB of usable storage, with one drive's worth of capacity used as distributed parity. In RAID 6, two drives are used for parity, leaving two drives' worth of usable capacity — four 8TB drives in RAID 6 yields approximately 16TB usable. If maximizing capacity is the priority over redundancy, RAID 5 is the practical choice for 4-bay setups with regular offsite backups.

Can I run multiple services on a 4-bay NAS at once?

Yes — Plex, backup agents, Docker containers, and file sharing can all run simultaneously on a 4-bay NAS. RAM is usually the first bottleneck. The QNAP TS-464 ships with 8GB DDR4 and supports up to 16GB, making it well-suited for multi-service workloads out of the box. The Synology DS923+ ships with 4GB ECC DDR4 and supports up to 32GB, giving it the most headroom for virtualization and container-heavy setups when RAM is expanded.

Should I choose Synology or QNAP for a 4-bay NAS?

Synology has better software polish, a more consistent update track record, and a simpler setup experience — ideal for users who want a NAS that works reliably without ongoing tinkering. QNAP typically offers more hardware features at the same price point — faster CPUs, more default RAM, built-in 2.5GbE — and suits users who want to push the hardware further or who value hardware transcoding. Both ecosystems are excellent; the decision usually comes down to whether you prioritize software quality and ecosystem consistency (Synology) or hardware specifications per dollar (QNAP).

How long does RAID 5 rebuild take on a 4-bay NAS?

Typically 12–48 hours for large drives, depending on drive capacity, drive speed, and how much read/write activity is happening on the NAS during the rebuild. A 4-bay NAS rebuilding 16TB drives under light load might take 20–30 hours. During a RAID 5 rebuild, the array is fully vulnerable to a second drive failure, which would destroy all data. This is why RAID 6 matters for large drives, and why regular offsite backups remain important regardless of RAID level.