File serving is one of the lightest jobs in computing. Almost any PC from the last twelve years can do it — the failures come from three specific weak points, not from the PC being old.
Before you buy anything, audit the old PC against this list. A file server does not render, calculate or think — it receives files and hands them back. That means the processor is almost never the problem. The parts that actually decide your experience are the network port, the disks and the RAM, in that order. Here is what is genuinely enough, and what is marketing.
Any 64-bit dual-core processor — an old Core i3, i5 or even a Pentium from the last decade — can saturate a gigabit network with plain file sharing. Windows sharing and TrueNAS both run happily on hardware that feels too slow as a desktop. Where CPU starts to matter is extras: media transcoding, many simultaneous users, or heavy antivirus scanning. For a pure file server for up to twenty people, stop worrying about the processor and spend your attention (and money) below.
For the Windows method, 8 GB RAM gives a comfortable machine that also runs updates and antivirus without swapping. For TrueNAS, 8 GB is the documented minimum — ZFS uses RAM as its read cache (the ARC), so more RAM genuinely means faster repeat access, and 16 GB is the sweet spot for a busy office. What does not work: 4 GB with TrueNAS, or a Windows server that also doubles as someone's daily desktop. A server that is also a workstation fails at both jobs.
Two rules. First, the operating system goes on a small SSD — even 120 GB — so the server boots fast and stays responsive while the big disks serve files. Second, for data, two hard disks as a mirror (Windows Storage Spaces or a TrueNAS mirror) mean one disk can die without the office stopping. Check any recycled disk's health before trusting it — a disk already showing warnings in CrystalDiskInfo belongs in the bin, not in the server. A file server built on a dying disk is a data-loss appointment.
This is the check everyone skips. Many old PCs and most old office switches are 100 Mbps, which caps copies near 11 MB/s — a 2 GB file takes three minutes and the staff will call your new server slow on day one. The server needs a gigabit port, a gigabit switch port and at least Cat5e cable between them. Wi-Fi is for clients, never for the server itself: cable the server to the switch, always. If the old PC lacks gigabit, a PCIe or USB 3 gigabit adapter costs little and transforms it.
A file server runs 24×7, and old towers are thirsty: a ten-year-old desktop can idle at 60–100 watts, which quietly adds a noticeable amount to the monthly electricity bill. A newer mini PC or a laptop-class machine idles at a fraction of that. Before resurrecting a very old tower, weigh its power draw against a small efficient machine — over three years, the electricity difference can exceed the price of the better hardware. Whichever you choose, put it on a small UPS: old or new, a power cut mid-write is its worst enemy.
Be honest about three disqualifiers. A power supply that is already flaky — random restarts will corrupt trust and possibly data. No gigabit option and no slot or USB 3 port to add one. And a machine so old that replacement fans, disks and power supplies cost more than a younger second-hand mini PC. Everything else — slow CPU, small case, no graphics card, an ugly beige box — does not matter at all for this job.
The video shows the file server methods running on ordinary hardware — watch what the builds actually use before you spend anything.
▶️ Watch Full VideoFor the Windows method with two or three light users, it survives. For TrueNAS it is below the documented 8 GB minimum and ZFS will feel starved. RAM is the cheapest upgrade you can give the build — go straight to 8 GB and remove the doubt.
No. After setup, both Windows (with remote desktop) and TrueNAS (web interface) are managed from another PC. Keep a spare monitor and keyboard for the install day and for emergencies, then let the server run headless.
For shared documents and office files, mirrored HDDs are the sensible spend — capacity is cheap and gigabit network is the ceiling anyway. Choose SSDs when many people open small files all day (accounts data, design work) or when noise matters, and never put the only copy of anything on a single disk of any kind.