How to choose a NAS: bays, network ports, and what the spec sheet leaves out

Introduction

If you are picking a NAS for your company, these three situations are probably familiar:

• The quotes make no sense: two vendors both quote an "8-bay NAS", the prices differ by a factor of two, and the spec sheets look much the same
• It filled up faster than expected: four bays were full within two years, and adding drives turns out to mean replacing the whole unit
• It is too loud for the office: the machine itself is fine, but nobody wants to sit next to it

Here is the blunt version: the hard part of choosing a NAS is not the brand, it is the bay count and the network ports. Get those wrong and the only fix is a new machine. File system, CPU and memory can all be worked around.

Every number in this article comes from the manufacturer-published specifications of the 122 NAS units in our hardware catalogue — 35 from Synology and 87 from QNAP — not from hearsay.

1. Decide the bay count first, not the brand

Bay count is the one specification you cannot add later. Drives can be swapped for larger ones and memory can usually be expanded, but the number of bays in the chassis is fixed.

Here is how the 87 QNAP units in our catalogue break down:

How to estimate: take your current data, multiply by three, then divide by what RAID leaves you.

Four bays in RAID 5 costs you one drive's capacity, so you keep three quarters; four bays in RAID 6 leaves you half. A four-bay unit with 4TB drives therefore gives roughly 12TB usable under RAID 5, not 16TB. Skip that step and every capacity figure comes out optimistic.

A common misunderstanding: RAID is not a backup. RAID keeps you running when a drive dies. It does nothing about accidental deletion, ransomware, theft or fire. The floor for backup is 3-2-1: three copies, two kinds of media, one off-site. The NAS is usually two of those, not all of them.

Think about expansion units early: if you expect to grow, pick a model that supports them — adding a shelf later is cheaper than replacing the unit. But expansion units are generally tied to the same brand and generation of interface, so that decision has to be made when you buy the head unit, not afterwards.

2. Network ports: 1GbE is history

This is the most overlooked specification and the one that most directly decides whether the thing feels fast.

Across the 87 QNAP units in our catalogue: 81 have 2.5GbE, 68 have 10GbE, 33 have 5GbE, 23 have 25GbE — and only 5 are 1GbE only.

In other words 2.5GbE is now the baseline for this generation, not a paid upgrade.

The point is that the bottleneck moves. Buy an eight-bay unit, fill it with eight drives, then connect it over 1GbE and none of that drive performance reaches you — it all queues behind the network. The reverse is just as wasteful: 10GbE on a two-bay unit is money you will not get back.

One more thing that gets missed: 2.5GbE on the NAS does not mean you get 2.5GbE. Your switch and the port on your computer have to match. If any one of the three is 1GbE, the whole path is 1GbE.

3. File system: that lower-case h in the model number

Of the 87 QNAP units in our catalogue, 32 carry a lower-case `h` in the model number: `TS-h1277AFX`, `TS-h1065eU`, `TDS-h2489FU`, the `ES-h` series.

That `h` means the unit ships with QuTS hero, the ZFS-based operating system. Models without it run standard QTS.

⚠️ To be precise about this: the manufacturer's hardware specification table has no "file system" field — the above is inferred from the model naming. Confirm against the vendor's product page and firmware version.

The value of a file system like ZFS is in catching data that has quietly gone bad: it checksums every block, repairs what it finds wrong on read, and brings snapshots and compression with it. The cost is a bigger appetite for memory, and the fact that once a storage pool is created that way, changing your mind means rebuilding it.

In practice the judgement is simple: if you are storing accounting records, design masters or original footage — things that cannot be recreated — this is worth attention. If the NAS mostly holds shared working files while the real data lives in the cloud or another system, an ordinary file system is enough, and the budget is better spent on bays and backup.

4. ECC memory: the two product lines are weighted differently

This was the clearest difference to emerge once we had all 122 units side by side:

• Of Synology's 35 units, 27 (77%) ship with ECC system memory
• Of QNAP's 87 units, 24 (28%) do

This does not make one better than the other; the product lines are simply weighted differently. The Synology range in our catalogue leans towards enterprise and rackmount models, while QNAP covers everything from small desktop units up to enterprise dual-controller systems, so the proportion of non-ECC models is naturally higher.

ECC memory deals with bit errors in memory itself. Whether you need it comes down to one question: if a single undetected error appeared in the data on this machine, how bad would that be? For an accounting database, a long-term archive or raw surveillance footage, it is worth paying for. For departmental working files that could be recreated from elsewhere, it may not be.

5. What the spec sheet will not tell you

This section is what we most wanted to flag after actually going through all 122 specifications.

Noise: only one vendor publishes it

All 35 Synology units list a noise figure, ranging from 14.6 to 23.8 dB(A) for desktop models. QNAP's hardware specification table has no such field.

This does not matter in a machine room and matters a great deal in an office — 14.6 dB(A) and 23.8 dB(A) are entirely different experiences from the next desk, and most of the noise comes from the drives and fan speed rather than the chassis. If the NAS is going in a room where people work, ask about this directly; do not assume that an absent figure means a quiet machine.

Power draw: the two measure it differently, so the numbers are not comparable

• Synology lists two figures: "access" and "drive hibernation". The DS124, for example, is 10.69 W and 3.44 W
• QNAP lists "power consumption, operating mode, typical", noting that it was measured fully populated. The enterprise ES2486AFdc, for example, is 754.61 W

A 750 W machine that never gets switched off is not a rounding error on the electricity bill. Power draw also maps directly onto heat and noise — those three are three descriptions of the same thing.

The bay count on the spec sheet is empty

Every specification describes the machine alone. Fill a 24-bay unit with enterprise drives and the drives usually cost more than the machine. Budget for the drives, and for the cycle of replacing them later.

Consumables on rackmount models

Power supply modules and fans are parts with a service life. Rackmount units often have redundant power (the `-RP` suffix) so that one failed supply does not stop the machine — which also means keeping spares.

6. Synology or QNAP

Both are mature. The difference is in trade-offs rather than quality:

In one line: if you want to spend less time choosing and simply buy something that will not be wrong, the shorter range is less work; if you already know the specification you want, the wider range will match it more closely.

7. Whether you need a NAS at all

There are cases where you do not, and it is better to say so:

• Small data, few people: two or three people sharing tens of gigabytes are better served by cloud storage, without having to manage drive lifespans
• Nobody owns it: a NAS needs someone watching drive health, confirming that backups actually ran, and applying firmware updates. With nobody responsible, it fails quietly — and usually you find out on the day you need it
• You want backup, not sharing: then the backup strategy comes first, not the hardware

Conversely, a NAS earns its place when data is growing, when several people need to work on the same files at once, when regulation or a contract requires the data to stay in-house, or with something that grows continuously by nature, such as surveillance recording.

The three questions we ask first

Before quoting a NAS we usually ask only three things, because the answers decide everything else:

1. How much data do you have now, and how much did it grow last year? This sets the bay count and drive size
2. Where will the machine live? A room with people in it, a machine room, or a cabinet — this decides rackmount or desktop, and whether noise matters
3. What happens if this data is lost? This decides ECC, ZFS, and how far the backup strategy has to go

Once those three are answered there are usually only two or three candidates left. We quote hardware on the actual configuration, including drives, cabinet and on-site installation.