NAS Buying Guide: How to Choose Your First NAS

The hard part of buying a first NAS is not choosing a model. It is working out which decisions you can revise later and which ones you are stuck with for the life of the machine. Memory, network cards and even drives can usually be changed. Bay count and the physical enclosure cannot. Get that ordering right and a modest first purchase lasts years; get it wrong and the second purchase arrives within eighteen months.

Start from the job, not the model

Three jobs dominate first NAS purchases, and they pull hardware in different directions.

A backup target is write-mostly, mostly sequential, and idle for twenty-three hours a day. It needs capacity and reliability, not speed. This is the least demanding job and the one most over-specified.

A file and media server is read-mostly and sequential. It cares about sustained throughput and network headroom, and it is where the gap between a gigabit port and anything faster becomes obvious.

An application host running containers, a photo index, or a database is random-IO heavy and memory-hungry. This is the job that punishes the fixed, non-upgradable RAM in cheap appliances, and the one most likely to justify building rather than buying.

Write down which of the three you actually need before comparing any two products. Most of the disagreement in NAS buying advice is people answering different questions.

Bay count is the decision you cannot undo

Adding capacity to a running array means either replacing every drive in a group with a larger one, or adding a whole new group. Both are expensive and slow. Buying an enclosure with more bays than today’s plan requires is by far the cheapest form of future-proofing available.

Bays	Realistic job	Redundancy available	Main limitation
1	Single-disk backup target, second copy of something else	None	A drive failure is total loss; only safe as one copy of several
2	Documents, photos, small household file server	Mirror	Half the raw capacity is redundancy, and it stays half forever
4	General household server, first sensible parity array	Single parity or two mirror pairs	Single parity across four large drives means a long, exposed rebuild
6 to 8	Media library, small office, mixed workloads	Double parity	Rebuild windows grow with drive size, not with bay count
12+	Multi-group arrays, capacity growth in stages	Double parity per group	Power, cooling, controller lanes and noise all become real design problems

Two figures matter more than the headline bay count. The first is how much usable space remains after redundancy: a two-bay mirror gives you one drive of usable capacity no matter which drives you fit. The second is the rebuild window, which scales with the size of each drive rather than with the number of them. A four-bay box full of 20 TB drives has a far longer exposed rebuild than a four-bay box of 4 TB drives, which is the real argument for double parity as capacities climb.

Buy an appliance or build one

An appliance NAS from Synology, QNAP, Asustor or similar arrives with a supported operating system, low idle power, a small footprint and a warranty on the whole machine. What you give up is choice: the CPU, the network port and usually the memory ceiling are fixed at purchase.

Building your own trades that convenience for PCIe lanes, ECC memory support, faster networking and any chassis you like. The tradeoffs are covered in detail in sizing NAS hardware around bays, HBAs, ECC memory and power, which is the piece to read before ordering parts. The short version: a build only pays off if you actually need something the appliance cannot give you, and “faster CPU” is rarely that thing.

The NAS chassis drive bay and PCIe lane sizer on this site will turn a raw capacity target into a bay count, a lane budget and a peak power figure, which is a faster way to sanity-check a shortlist than reading spec sheets side by side.

Drives: count first, capacity second

Decide how many drives the array will hold before deciding how large each one is. The redundancy math depends on the count; the capacity is then simple arithmetic against your target.

Two drive specifications matter more than the marketing tier. The first is recording technology. Shingled recording collapses under the sustained random rewrites that a parity array performs during a rebuild, and it belongs nowhere near one. Western Digital’s product brief lists the entire WD Red Plus range as CMR, and the reasons this distinction is worth checking on every purchase are set out in CMR vs SMR NAS drives.

The second is the annualised workload rating, which is the amount of data the manufacturer expects to be read from or written to the drive per year. Western Digital rates WD Red Plus at 180 TB per year with a stated MTBF of one million hours, a non-recoverable read error rate below 1 in 10^14 bits, and a three-year limited warranty. Desktop drives are routinely rated at a fraction of that. For a machine that is powered on continuously, the workload figure is the specification that separates a NAS drive from a cheaper one with the same capacity on the label.

Reasonable starting points are the WD Red Plus range and the Seagate IronWolf range. Both ship in many capacities, so buy the capacity your bay count and target require rather than the one at the top of a search results page.

Memory, and why the cheap boxes hit a wall

Appliance memory is often soldered. A Synology DS124 ships with 1 GB of non-ECC DDR4; a DS223 ships with 2 GB. That is ample for file sharing and backup, and it is the constraint that bites the moment you add a photo index, several containers, or a database.

ECC memory is a separate question from capacity. It detects and corrects single-bit errors rather than letting corrupted data reach the array, which matters on a machine whose entire purpose is holding data for years. Appliance NAS units in this price class do not offer it; builds can, provided the CPU, chipset, board and modules all support it. TrueNAS documents its own memory guidance for builds, and the tradeoff is discussed further in the hardware sizing guide.

The network port is the ceiling nobody reads

A single gigabit port carries 1000 Mb/s, which is 125 MB/s before any protocol overhead and roughly 113 MB/s of file data in practice. That number is the ceiling on every transfer to and from the machine, regardless of how many drives sit behind it. A four-drive array will saturate a gigabit link without effort.

Two consequences follow. First, if large-file speed matters to you, check the port before checking the CPU. Second, link aggregation does not fix it. Synology’s own knowledge base article on exactly this question states that total network bandwidth “will only increase if there are multiple clients”, because each client is answered by one of the bonded interfaces. Bonding two gigabit ports buys you two clients at a gigabit each, not one client at two. If transfers are already slower than that ceiling, work through NAS slow transfer speeds before buying anything.

Power, spin-up and the UPS

Steady-state draw is not the number that sizes a power supply. Western Digital’s brief lists 12 V peak current of 1.9 A for the 12 TB WD120EFGX against average read/write consumption of 8.8 W and idle consumption of 6.1 W. That peak works out to roughly 23 W on the 12 V rail per drive during spin-up, against under 9 W once running. Eight drives starting simultaneously is a very different load from eight drives working.

Appliances hide this: Synology quotes 17.3 W during access for the DS223 with drives fitted, and 4.1 W once those drives hibernate. Builds do not hide it, and staggered spin-up exists specifically to spread that peak over several seconds.

If you are sizing a UPS, measure the machine rather than adding up datasheet numbers. A Kill A Watt P3 P4400 plugged in ahead of the NAS gives a real wall figure for idle, working and startup draw, which is the input a UPS runtime chart actually needs.

Reasonable first purchases

For a single-drive backup target, the Synology DS124 is a one-bay unit with 1 GB of non-ECC DDR4 and a single gigabit port. Treat it as one copy in a backup plan, never the only copy, because a single drive has no redundancy by definition.

For documents, photos and a modest household file server, the Synology DS223 is a two-bay unit with 2 GB of fixed non-ECC DDR4 and a single gigabit port, drawing a quoted 17.3 W during access and 4.1 W with the drives hibernating. Fitted as a mirror it gives one drive of usable capacity with tolerance for one drive failure. Raw capacity is whatever two supported drives come to, so check the current drive compatibility list rather than assuming a ceiling.

It is a 2023 model, and the newer DS225+ is worth the comparison precisely because it moves the two limits this article keeps returning to. Its 2 GB of DDR4 stays onboard, but a single SODIMM slot takes the machine to 6 GB (2 GB + 4 GB), and it adds a 2.5GbE port alongside the gigabit one. If the plan is file sharing and backup, the DS223 is the cheaper answer and stays correct. If containers or a photo index are anywhere in the plan, the upgradable memory is the difference between a machine you can rescue and one you replace.

For four bays and up, compare an appliance against a build honestly. Once you are buying a four-bay enclosure and four NAS drives, the price gap narrows and the build starts to buy real things: more memory, ECC support, faster networking, and a chassis you can still expand in five years.

A short pre-purchase checklist

• Which of the three jobs is this machine for, and is anything on the shortlist specified for a different one?
• How much usable capacity remains after redundancy, and does that still meet the target?
• Are all candidate drives CMR, and does the workload rating match a continuously powered machine?
• Is the memory upgradable, and does the planned software fit in what ships?
• What is the network port, and is that ceiling acceptable for the largest transfer you care about?
• Does the enclosure have bays you are not filling yet, and can the power supply start every drive at once?

Spending a little more on bays and a little less on the processor is the version of this decision that ages well.