Both give you bays of capacity outside the machine. The difference is what sits between the drives and the computer, and it changes almost everything else.
Direct-attached storage connects over a cable and appears as a local disk. Network-attached storage connects over Ethernet and appears as a share.
That distinction decides bandwidth, latency, who can reach it, and — the part people find out later — whether anyone notices when a drive dies.
The specifications
| Product | Storage | Best for | Price class | Where to buy |
|---|---|---|---|---|
| OWC ThunderBay 4 OWC | 4 bays accepting 3.5-inch HDDs or 2.5-inch SSDs | Local dataset capacity at Thunderbolt speed, attached to one machine | Upper mid-range ($1,000–$2,000) | Check Price on Amazon OWC ThunderBay 4 at Amazon — opens in a new tab |
| UGREEN NASync DXP4800 Plus UGREEN | 4 × 3.5" SATA bays plus 2 × M.2 NVMe | Serving datasets and model archives over 10-gigabit without a drive-compatibility whitelist | Upper mid-range ($1,000–$2,000) | Check Price on Amazon UGREEN NASync DXP4800 Plus at Amazon — opens in a new tab |
| TerraMaster D5-300C TerraMaster | 5 bays for 3.5-inch or 2.5-inch drives | Cheap bulk capacity attached to one machine over USB | Budget (under $500) | Check Price on Amazon TerraMaster D5-300C at Amazon — opens in a new tab |
Bandwidth: DAS wins, and by more than you would expect
The counter-intuitive result, because 10-gigabit networking sounds fast.
| Connection | Realistic throughput |
|---|---|
| USB 3.2 Gen 2 DAS | ~1,000 MB/s |
| 10 GbE NAS | ~1,100 MB/s |
| Thunderbolt 4 DAS | ~2,500–3,000 MB/s |
A Thunderbolt enclosure delivers roughly two and a half times a 10-gigabit network share, and it does so without a switch, without network adapters in every machine, and without protocol overhead.
If the storage is flash rather than spinning disks, that gap is real and you will feel it. If the storage is four mechanical drives producing 400 MB/s, neither connection is the bottleneck and the comparison is moot.
Latency: the difference that matters for datasets
Less visible than bandwidth and more consequential for one specific workload.
A local disk answers in well under a millisecond. A network share adds a round trip plus protocol overhead — usually a fraction of a millisecond on a good local network, and it is per-operation.
For large sequential reads — pulling a 42 GB model file — this is irrelevant. Throughput dominates and the network keeps up.
For many small files — an image dataset with hundreds of thousands of items, streamed during a training run — it is not irrelevant at all. Each file is an operation, each operation pays the latency, and the network share can end up starving the GPU while the local disk would not.
If you train on file-per-sample datasets, that alone points at DAS. If your data is in a handful of large archives, it does not.
Sharing: NAS wins outright
The axis DAS cannot compete on, because it is definitional.
Direct-attached storage belongs to one machine at a time. Moving it means unplugging it, and the machine it was attached to loses it. If you have a workstation and a laptop, or a workstation and a homelab node, DAS serves one of them.
A NAS serves everything on the network simultaneously — the workstation, the laptop, the inference node, the media player, the backup job. That is usually the reason people buy one.
Protection: NAS wins, and this is the underrated one
Not redundancy — both can do RAID — but knowing about it.
A NAS runs a filesystem designed for the job. ZFS or btrfs checksums every block and scrubs on a schedule, so silent corruption is detected rather than propagated. It emails you when a drive reports errors. It has a dashboard showing pool health. It takes snapshots.
A DAS enclosure typically has none of that. RAID is either a basic hardware mode selected by a physical switch, or host software that depends on the machine staying healthy. Crucially, a failed drive in a DAS box frequently goes unnoticed — there is no monitoring, no alerting, and no dashboard. People discover the first failure when the second one takes the array.
If the data matters, that difference is larger than any bandwidth figure.
The other differences
Backup. A NAS can run its own backup jobs to another location on a schedule, without the workstation being on. DAS is backed up by whatever machine it is attached to, when that machine is running.
Power. A NAS runs continuously — roughly 30–40 W with four drives spinning. A DAS enclosure can be switched off with the machine, which over a year is a genuine saving if you do not need the storage always available.
Cost of entry. DAS is cheaper: an enclosure and drives. A NAS costs more for the unit, and 10-gigabit networking means a switch and adapters on top. See Best 10GbE Switches for what that actually adds up to.
Complexity. DAS plugs in. A NAS is a small server with a filesystem, users, permissions, shares and updates. That is a feature and a maintenance commitment.
The recommendations
If direct-attached is the right shape
Best for Developers
OWC ThunderBay 4
Best for Local dataset capacity at Thunderbolt speed, attached to one machine
Direct-attached storage sidesteps the network entirely: no switch, no adapters, no protocol overhead. The trade is that it belongs to one machine, and moving it means unplugging it.
- Storage
- 4 bays accepting 3.5-inch HDDs or 2.5-inch SSDs
Strengths
- Thunderbolt bandwidth well beyond 10-gigabit networking
- No network stack in the path, so no SMB or NFS overhead
- No switch or network adapters to buy
- Four bays takes it well past what an internal drive can hold
Trade-offs
- Attached to one machine at a time
- Software RAID depends on the host, so a host failure is an event
- Thunderbolt host required
- Fan noise under load
Four bays at Thunderbolt speed, appearing as local storage. For a single workstation doing dataset work, this is faster than anything a network can offer and simpler than anything a NAS requires.
The trade is that it belongs to that workstation, and that its RAID depends on the host machine remaining healthy.
Best Budget
TerraMaster D5-300C
Best for Cheap bulk capacity attached to one machine over USB
The cheapest route to five bays of capacity. USB rather than Thunderbolt means less bandwidth, and for spinning disks that is rarely the limit anyway.
- Storage
- 5 bays for 3.5-inch or 2.5-inch drives
Strengths
- Five bays for a fraction of the price of a NAS
- USB-C, so it works with almost any machine
- Hardware RAID modes without host software
- No network configuration at all
Trade-offs
- USB bandwidth, not Thunderbolt
- Single-machine, like all direct-attached storage
- Build quality reflects the price
- No redundancy monitoring or alerting
The budget version: five bays over USB-C with basic hardware RAID modes selected by a switch. Less bandwidth than Thunderbolt, which for mechanical drives is rarely the limit anyway, and considerably cheaper.
If network-attached is the right shape
Best for Homelabs
UGREEN NASync DXP4800 Plus
Best for Serving datasets and model archives over 10-gigabit without a drive-compatibility whitelist
10 GbE and NVMe caching at a price the established vendors do not match, and no restrictions on which drives you may fit. The software is younger than the competition, and that is the trade.
- Memory
- 8 GB
- CPU
- Intel Pentium Gold 8505 — 5 cores, 6 threads
- Storage
- 4 × 3.5" SATA bays plus 2 × M.2 NVMe
Strengths
- 10 GbE onboard, which most NAS units at this price lack
- Expandable to 64 GB of DDR5
- Two NVMe slots for cache or fast tiers
- No first-party drive whitelist
Trade-offs
- Software ecosystem is newer and less proven
- Smaller third-party application catalogue
10-gigabit networking is the specification that decides whether a NAS is convenient or theoretical — 40 seconds to pull a 42 GB model against six minutes over gigabit. Two NVMe slots allow a cache tier, and memory expands to 64 GB.
The full treatment is in Best NAS for AI Developers, and the drives to put in it are covered in Best NAS Drives for AI Datasets.
Backup, which the two shapes make differently easy
Neither RAID nor a redundant DAS array is a backup — both write a deletion through to every copy instantly. What differs is how easily each fits into a real backup arrangement.
A NAS backs itself up. It can run scheduled jobs to a second location — another NAS, an external drive, or cloud storage — without the workstation being switched on, and it can hold snapshots so that an accidental delete or a ransomware event is recoverable rather than propagated.
A DAS enclosure is backed up by whatever it is plugged into, when that machine is running and remembers to. That is workable and it is one more thing depending on you.
For the three-copy rule this matters. Model weights are re-downloadable and need no protection at all. Your own datasets, fine-tuned adapters and training runs frequently cannot be recreated, and those are the files that want a second copy somewhere else.
What happens when the host dies
The DAS failure mode people do not anticipate.
If the array is host software RAID, the array’s configuration lives on the machine, not in the enclosure. A failed motherboard or a corrupted operating system means recovering the array on a new host — usually possible, occasionally not, and never at a convenient moment.
Hardware RAID inside the enclosure avoids that and introduces its own version: the array is now tied to that controller, and a dead enclosure means finding a compatible replacement.
A NAS keeps the pool configuration on the drives themselves. Move a ZFS pool to different hardware and it imports. That is a meaningful difference in a recovery scenario, and it is not something you discover until you are in one.
The winner, by scenario
| Your situation | Winner | Why |
|---|---|---|
| One workstation, large datasets | DAS | More bandwidth, lower latency, no network to build |
| Training on file-per-sample datasets | DAS | Per-operation latency starves the GPU over a share |
| Several machines need the same data | NAS | DAS serves one machine, definitionally |
| The data is irreplaceable | NAS | Checksumming, scrubbing and alerting — you find out |
| Model archive you pull from occasionally | NAS | Convenience beats throughput here |
| Lowest cost of entry | DAS | No switch, no adapters, no unit |
| You want it backed up automatically | NAS | It can run its own jobs, unattended |
| Simplest possible setup | DAS | It is a cable |
The verdict
Buy DAS if one machine does the work. It is faster, cheaper, simpler, and for a workstation crunching local datasets it is the better tool by a clear margin.
Buy a NAS if more than one machine needs the data, or if losing it would matter. The sharing is definitional and the monitoring is the part people underestimate — a drive that fails silently in a DAS enclosure is a problem you discover at the worst possible moment.
Many people end up with both, and it is a coherent arrangement rather than a compromise: fast local capacity attached to the machine doing the work, and a NAS as the shared archive and backup target. They solve different problems.
What we would avoid is a DAS enclosure holding the only copy of anything, without a monitoring habit to compensate. RAID is not a backup in either case — but at least a NAS tells you when it is unhappy.
Common questions
Which is faster, NAS or DAS?
DAS, usually by a wide margin. A Thunderbolt enclosure delivers around 2,500–3,000 MB/s against roughly 1,100 for a 10-gigabit network share. If the storage is mechanical drives producing 400 MB/s, neither is the bottleneck and it does not matter.
Can I share a DAS between two computers?
Not simultaneously. Direct-attached storage connects to one machine at a time — that is what “direct-attached” means. You can unplug and move it, and the machine you took it from loses access. If two machines need the data, you want a NAS.
Is a NAS worth it for one person?
It depends on whether the data matters and whether more than one device needs it. For a single workstation with replaceable data, DAS is faster, cheaper and simpler. For anything irreplaceable, a NAS’s checksumming, scrubbing and alerting are worth more than the bandwidth you give up.
Why does latency matter for datasets?
Because training on file-per-sample data turns every file into a network operation, and each pays the round-trip cost. With hundreds of thousands of small files that adds up enough to starve the GPU. Pulling one large model file is throughput-bound and unaffected.
Do I need 10-gigabit for a NAS?
Only if the storage can fill it. A four-drive mechanical array produces 300–500 MB/s and 2.5 GbE already carries 280. If the NAS is NVMe-backed or has a cache tier, 10 gigabit is the tier that keeps up — see our 2.5GbE vs 10GbE comparison.
Is RAID in a DAS enclosure trustworthy?
It works, with two caveats. Host software RAID depends on that machine staying healthy, so a host failure becomes an event. And most enclosures have no monitoring at all — no alerting, no dashboard, no scrub — so a failed drive can sit unnoticed until a second failure takes the array.
Continue your research
- Best NAS for AI Developers — if network storage is the answer
- Best NAS Drives for AI Datasets — what goes in either one
- 2.5GbE vs 10GbE — the network a NAS depends on
- Best NVMe SSDs for AI Workloads — local storage inside the machine