TerraMaster D4-320 vs Synology DS425+

For a four-bay purchase, the Synology DS425+ is the pick when household devices need shared files, backups and media without depending on any one computer: it is a self-contained network-attached storage appliance. The TerraMaster D4-320 is the pick when the storage lives beside a single computer: it is a direct-attached USB enclosure, not a NAS, and it is the budget path to four drive bays. They share a bay count and nothing else, so the real decision is who serves the files and who rebuilds after a drive dies.

Quick choice

• 4drive bays in both
• 10 Gbpsshared USB 3.2 Gen 2 link on the D4-320
• 2.5GbEfastest of the DS425+'s two Ethernet ports
• 6 GBmaximum DS425+ memory, from 2 GB installed

Same bay count, different products

The DS425+ is a computer: an Intel Celeron J4125 with 2 GB DDR4 memory (expandable to 6 GB), running Synology's DSM, with a 2.5GbE port, a 1GbE port and two M.2 2280 NVMe slots alongside its four SATA bays. The D4-320 is a dumb-but-fast box: TerraMaster's own spec table lists its network interface and hardware RAID as "/" (not present), and its interface is a single USB 3.2 Gen 2 Type-C link rated up to 10 Gbps, shared by all four installed disks.

Both accept 3.5-inch SATA hard drives and 2.5-inch SATA SSDs, so the drives, not the enclosures, set your raw ceiling. TerraMaster quotes individual drives up to 32 TB for a total capacity of 128 TB; Synology quotes up to 96 TB of raw storage for the DS425+ using 24 TB drives. Neither figure is usable space: parity, filesystems and your backup copies come out of it.

• Yes: DS425+: serves files to the network by itself, with no host PC involved
• Yes: DS425+: runs its own backup jobs, photo library and surveillance for up to 40 IP cameras at 1080p
• Yes: DS425+: expands its storage pool by adding a hard drive or migrating RAID 1 to RAID 5
• No: D4-320: no network interface; a connected computer must share any files
• No: D4-320: no RAID; four independent disks with no fault tolerance
• Partly: D4-320: can act as expansion for a TerraMaster NAS running TOS 5.1 or later

For a deeper treatment of this split, see NAS vs DAS; for other four-bay options between these two extremes, see our best 4-bay NAS guide.

If household devices need the files: Synology DS425+

The DS425+ answers the "best 4 bay NAS" question for most homes because everything after the drives is included: the operating system, the file services, the backup engine and the permission model. Its specifications, from Synology's DS425+ page:

• Intel Celeron J4125, 2 GB DDR4 non-ECC (one slot, 6 GB maximum by adding a 4 GB module)
• 4x 3.5" SATA hard-drive or 2.5" SATA SSD bays, plus 2x M.2 2280 NVMe slots for SSD cache or M.2 storage pools
• 1x 2.5GbE and 1x 1GbE Ethernet, 2x USB 3.2 Gen 1 ports
• Synology Hybrid RAID plus Basic, JBOD, RAID 0, 1, 5, 6 and 10, with migration from RAID 1 to RAID 5 and volume expansion by adding a hard drive
• Up to 278 MB/s read and 281 MB/s write, per Synology's internal testing
• 3-year hardware warranty, extendable to 5 years with Extended Warranty Plus

The four-drive order: start with two equal drives in SHR and grow. Four-drive RAID 5 arrays hold the capacity of all drives minus one, and the array survives one disk failure. Add the fifth disk's worth of money to your backup budget instead: Synology builds Hyper Backup around 3-2-1 configurations with bare-metal backups to local and remote servers, external drives or cloud destinations, and the two USB 3.2 Gen 1 ports give a destination for a rotation of external drives.

The trade-offs: 2 GB of RAM is the entry point, the second network port is 1GbE only, and M.2 storage pools and cache still require drives on Synology's compatibility list even though DSM 7.3 allows third-party SATA drives for installation and pools on 2025 model-year Plus units. Synology includes two Surveillance Station camera licenses; more cameras require paid licenses, and higher resolutions reduce the maximum channel count. Synology's own noise figure is 21.6 dB(A), measured idle with SSDs installed.

Check price on Amazon

If storage lives at one computer: TerraMaster D4-320

The D4-320 is not a lesser DS425+; it is a different tool that happens to cost less. TerraMaster's product page describes it as a plug-and-play USB storage device with four individual disks, no drivers, and compatibility with Mac, Windows and Linux. Its USB Type-C interface works with USB 3.0, USB 3.1, USB 3.2, Thunderbolt 3 and Thunderbolt 4 host ports, and a 1-meter Type-C to Type-C cable is included.

• 4x 3.5"/2.5" SATA bays, single-disk mode only; no hardware RAID
• USB 3.2 Gen 2 at up to 10 Gbps, shared across the disks; TerraMaster cites up to 1,016 MB/s combined read with four drives installed
• Hot-swappable, tool-free push-lock drive trays
• 2-year warranty; noise level 17.3 dB(A) with drives in standby, per TerraMaster's test conditions

The four-drive order: four independent NAS-rated drives, one filesystem each. With four 8 TB disks you get 32 TB of total, unprotected space, and a failed disk costs you exactly that disk's contents — so the money a Synology buyer spends on parity goes instead into a second copy of anything irreplaceable. TerraMaster's own Windows backup client, TPC Backupper, can schedule folder and partition backups to the D4-320, but versioned, deduplicated backup destinations are host software's job here, not the enclosure's.

Because there is no D4-320 ASIN verified from the maker's own pages yet, we link TerraMaster's product page rather than an Amazon listing: confirm the exact model and included cable on the maker's page when ordering. TerraMaster also warns buyers to check its hard drive compatibility list before purchasing; the list marks the Seagate IronWolf ST8000VN004 and WD Red Plus WD80EFPX (both 8 TB) as recommended for the D4-320, with IronWolf models from 4 TB up to 20 TB listed. Our NAS hard drive guide covers those drive families in detail.

At four equal drives: capacity and risk side by side

1. 1

   Decide who serves the files

   If any device other than one computer needs them, that decides DS425+ before capacity does.

2. 2

   Pick drives from official lists

   Match the maker's compatibility list: ST8000VN004 or WD80EFPX for the D4-320; Synology's list plus the DSM 7.3 third-party SATA policy for the DS425+.

3. 3

   Budget for a second copy

   Four independent disks mean four separate failure domains; parity is not a backup on either box.

4. 4

   Rehearse the restore

   Know where the backup lives (external USB drives, another machine or cloud) and confirm the restore path before the first failure.

Support, warranties and replacement planning

Synology covers the DS425+ with a 3-year hardware warranty, extendable to 5 years with Extended Warranty Plus (available in Europe and North America, purchased within 90 days of the device purchase). TerraMaster covers the D4-320 with a 2-year warranty. On the drive side, plan replacement parts for the whole service life you expect: TerraMaster's compatibility list is enclosure-specific and the DS425+'s M.2 slots carry the strictest rules of anything in this comparison. If a drive fails in year three, the DS425+ owner rebuilds the array and restores the backup; the D4-320 owner restores from wherever that disk's second copy lives — which is why the independent-backup step above is not optional.

• TerraMaster D4-320, drives in standby17.3dB(A)
• Synology DS425+, idle with SSDs installed21.6dB(A)

Source: each maker's published figures; the test setups differ, so treat this as a rough comparison

Holiday deal checklist

Sales events compress the decision; they don't change it. When either box is discounted:

• Compare complete kits, not chassis prices. A four-bay "deal" without drives is a different purchase from one bundled with disks; our capacity and risk table only holds at equal drives.
• Check the exact model and revision. TerraMaster sells the D2-320, D4-300 and D4-320 alongside each other; the D4-320 is the 10 Gbps generation.
• Confirm the warranty clock. Synology's warranty starts on the purchase date on your receipt, which matters for a gift bought in November and unwrapped in December.
• Spend the savings on a backup destination. Whatever the discount, a second copy of irreplaceable files is the part of the basket no sale includes.

Budget-focused buyers should also read our best NAS under 500 guide before committing, and our home NAS guide covers smaller two-bay alternatives.

How we choose

We have not physically tested either enclosure. Every specification here comes from the makers' own pages — Synology's DS425+ product page and DSM 7.3 announcement, TerraMaster's D4-320 product page and drive compatibility list — linked in each section and checked against the source snapshots we saved during research. Capacity and RAID arithmetic follows the makers' published modes and figures; usable-space numbers are calculated, not measured. Picks reflect the file-serving and recovery requirements each product documents, not throughput claims. Full method: How we choose.

Verdict

Buy the Synology DS425+ if the storage belongs to a household: it is the file server, the backup engine and a documented, fault-tolerant array in one box, with a 3-year warranty. Buy the TerraMaster D4-320 if the storage belongs to one computer you already keep running: four independent bays on a 10 Gbps USB link for less money, provided you accept that redundancy, versioned backups and network sharing are jobs for your host and your own backup plan. Never confuse the two: the D4-320's bay count makes it look like a budget DS425+, but only the DS425+ answers "best 4 bay NAS" — the D4-320 answers "most drive bays per dollar at my desk."