DAS vs NAS: Storage Differences, Where SAN Fits and Which to Choose

DAS vs NAS vs SAN: the definitions

The storage industry body SNIA keeps a dictionary of these terms, and its definitions are short. Direct attached storage is a storage device locally connected to a server and dedicated to that server. Network attached storage is a storage device that connects to a network and provides file access services to clients.

The practical difference follows from the second row. A DAS belongs to one machine: whatever that machine can do with its own drives, it can do with the DAS. A NAS is a device in its own right, running its own file services, so any client on the network can reach the same files without another computer in between. QNAP's own beginner's guide puts it the same way: a NAS connects to a network and allows multiple users and devices to access files at the same time.

SAN is the third term people meet. SNIA defines a storage area network as a network whose primary purpose is the transfer of data between computer systems and storage devices, and notes that the term is usually, but not necessarily, identified with block services. A NAS hands out files; a SAN is a network that carries storage traffic, typically as blocks.

How a NAS serves files: the protocols

The file services are what make a NAS a NAS, and the maker's specification sheet tells you which ones you get. Synology says its DSM software supports FTP, SMB2, SMB3 (encrypted), AFP, NFS and WebDAV, and provides file sharing across Windows, macOS and Linux. Its DSM 7.4 specification adds end-to-end SMB1, SMB2 and SMB3 encryption and notes that NFS version 4.1 is only supported on specific product models.

That last line is the kind of detail to check before buying. If your clients rely on a particular protocol version, confirm it against the specification for the exact NAS model, not the software family. A DAS needs none of this: the computer it is attached to provides whatever sharing it offers.

Where the line falls: enclosures that are DAS, NAS add-ons or both

Multi-bay boxes blur the line, and the makers' own product pages show where it sits. Three examples from QNAP and Synology cover the cases you are likely to meet, including one where the maker's page says two different things.

• QNAP TR-004: four 3.5-inch SATA bays on USB 3.2 Gen 1 Type-C. QNAP says it can expand a QNAP NAS and can also be used as a DAS device, and that it can switch between hardware- and software-controlled RAID modes.
• QNAP TL-D800C: eight 3.5-inch SATA bays on USB 3.2 Gen2 Type-C, up to 10 Gb/s. QNAP's page lists its supported systems as QNAP QTS/QTS hero, Windows and Linux, yet a note on the same page says the TL-D800C only supports QNAP NAS running QTS 4.4.2 or above, or QTS hero. On a NAS, QNAP says NAS applications cannot be installed on it and that it can only be used as an individual storage pool or volume.
• Synology DX525: adds five drive bays to a Synology DiskStation, with its volumes managed through the host NAS's DiskStation Manager.

The pattern is consistent where the makers are consistent. A box that runs no file services of its own is storage attached to something else: to one computer, which makes it a DAS, or to a NAS, which makes it an expansion of that NAS. The DX525 is the clear add-on, managed from the host NAS. The TR-004 is documented for both roles. For the TL-D800C, QNAP's own page states both a computer-and-NAS list and a NAS-only note, and we do not choose between them: if you want it as a DAS on a Windows or Linux computer, confirm with QNAP before you buy.

Add-on boxes have a consequence for capacity planning. QNAP's TL-D800C note means that on a NAS its drives form their own pool or volume rather than merging into the NAS's existing one, so plan the RAID layout of such a box as a separate array. RAID 5 vs RAID 6 covers that choice.

A single external drive sits at the far end of the scale. QNAP's guide describes it as requiring a physical connection, typically to one device at a time, against a NAS that supports simultaneous access by multiple devices and users. A multi-bay DAS enclosure is a bigger version of the same arrangement: more bays, still one host.

DAS vs NAS storage: what changes for the drives

Drive makers write the use case into their data sheets, and the two ends of the range differ. Seagate's BarraCuda 3.5-inch data sheet lists home servers and entry-level direct-attached storage devices among the drive's best-fit applications, and the same table lists the 3TB to 8TB models as SMR. Seagate's IronWolf Pro data sheet gives Unlimited as the drive bays supported for its 16TB to 24TB models.

So a desktop-class drive whose best-fit list includes home servers and entry-level DAS is not the same proposition as a NAS-class drive rated for any number of bays, even at the same capacity. Read the recording technology and the bay rating on the sheet for the exact part number before you fill a multi-bay box, whether it is a DAS or a NAS. Our pages on IronWolf Pro and cheap NAS drives list current Amazon.co.uk offers.

Direct attachment is also normal in servers. Microsoft's Storage Spaces Direct requirements describe direct-attached SATA, SAS, NVMe or persistent memory drives that are physically attached to just one server each, which Windows Server then pools across servers. DAS describes how a drive connects, not whether the build is small.

DAS vs NAS for Plex and a media server

We have not found a Plex document on storage, so this section makes no claim about Plex itself: nothing here is about transcoding, processor load or Plex's own settings. The definitions still settle the main question. If the media server runs on one computer and that computer is the only thing reading the files, a DAS attached to it fits the SNIA definition exactly: storage dedicated to that machine.

If other devices on the network also need to reach the same files directly, without going through the media server computer, that is what a NAS is for: QNAP's guide stresses simultaneous access by multiple devices and users, and Synology lists file sharing across Windows, macOS and Linux. Some NAS boxes take expansion units such as the DX525 when the bays run out, managed from the NAS itself.

For the drives in a media server's DAS, the BarraCuda sheet is a useful marker of where desktop drives sit: Seagate lists home servers among its best-fit applications, but its 3TB to 8TB models are SMR, so check the recording technology before you put several in a RAID set. Drive choice for a server build is covered on home server hard drive.

DAS vs NAS for a homelab

A homelab often has a server already, and that changes the sum. Attached to a server, a DAS such as the TR-004 adds bays to a machine that can run its own file services, which is the DAS-to-one-server arrangement SNIA describes. A separate NAS adds a second device that serves files on its own.

The drive class follows the role. Seagate lists home servers and entry-level DAS among the BarraCuda's best-fit applications, and gives its IronWolf Pro 16TB to 24TB Unlimited as the drive bays supported, so the size of the box you are filling is a reason to read the bay rating as well as the price.

If the server will build its own RAID or pool in software, the enclosure's RAID mode matters too. The TR-004 offers both hardware- and software-controlled RAID; hardware RAID vs software RAID covers which to pick, and homelab storage covers the wider build.

DAS or NAS: which to choose

• One computer uses the data: DAS. It is storage dedicated to that machine.
• Several clients need the same files over the network at the same time: NAS, which provides file access over protocols such as SMB and NFS.
• Mixed Windows, macOS and Linux clients: check the NAS maker's protocol list for the exact model; Synology notes NFS 4.1 is model-specific.
• A NAS that has run out of bays: an expansion unit managed by the NAS, such as Synology's DX525.
• Block storage shared across servers on a dedicated storage network: that is a SAN, a separate class of build from either.
• Any multi-bay box: check the drive's own data sheet for its recording technology and supported bays.

Our English pages go further into the hardware: DAS and RAID enclosures, USB DAS enclosures and NAS devices. Prices there are in US dollars from Amazon.com; the /uk drive pages linked above show Amazon.co.uk prices in pounds inc VAT.