Can you buy second-hand Synology on Xianyu? The accompanying person inspected three cars, and the serial number of the cheapest one was stolen

colleague Da Liu has been watching NAS for almost half a year, but he just can't bring himself to buy new ones—the new four-drive model costs over 4,000 yuan, while his budget is 2,000 yuan. Last month, he finally spotted a DS920+ on Xianyu, priced at 1900 yuan, 400 yuan cheaper than others. The seller's pitch was: "Retired from the company, forgot to take a stand when leaving, cheap deal." He almost took a photo directly, but I stopped him and said I'd pay after he finished the inspection. They looked at three models in total. The first was the cheap one. Upon checking the serial number, the product didn't match the machine's sticker—that machine was not the one it claimed to be. This article lays out the inspection methods for three machines, showing whether you can buy second-hand Synology and how to inspect it. After reading, you'll have a clear idea.

to clarify: the valuable thing about second-hand Synology isn't the metal box, it's the SN

many people don't understand why second-hand Synology holds its value so well. The DS920+ launched at 4,200 yuan, used for four years, and can still sell for 2,300 yuan on Xianyu, with over half residual value, making it more competitive than most electronic products. The reason is simple: Synology is not selling hardware, but the DSM system bound to serial numbers. The SN printed on the bottom of the device is the official credential of recognition—the package center, QuickConnect, Photo Station, and other real software values all follow SN. The CPU memory bays inside the metal box are actually parts that can be replaced or faked.

this directly determines that the inspection logic for second-hand Synology phones is different from that for phones. The main purpose of checking a phone is to prevent refurbished issues. Besides preventing refurbished NAS, you also need to guard against a local specialty— the 'monster phone.' A so-called 'demon phone' refers to generic hardware that has been flashed with pirated DSM, then has the SN and MAC of other machines written into the boot directory, making the system 'think it's a White Synology.' The appearance can be made exactly, and the system interface can be accessed, but that SN was stolen from another real machine. So the first thing to do when inspecting a second-hand Synology isn't about its condition, but about checking the serial number.

the first model failed: the serial number couldn't match the model after checking the official website

Da Liu had his eye on the 1900 "DS920+"—I had the seller take a photo of the label on the bottom of the device, and the SN code was clearly visible. Then open the warranty inquiry page on Synology's official website and enter the SN—the returned model is DS218+, an old machine with two bays, not a DS920+ with four bays. It was immediately clear that this was a monster phone. The shell and stickers were either a replica or assembly of the DS920+, and the SN code in the guide was copied from a real DS218+.

This is the core move of the demon detector. I call it SN Three Comparison :

all three spots matched, then it was time to judge the quality. This process also has a free-to-get advantage: the warranty inquiry also brings up the warranty expiration date . With a quick backward search, you can tell exactly when the machine was activated. It's clear at a glance whether the seller's claim of "two years of use" is true. It's similar to how I previously wrote about router inspections using SN to check warranty. If you're interested, you can refer my previous article about second-hand routers— are the same.

second unit is 300 cheaper: the cheaper is the fan and bracket

second is the DS918+, a 2018 old fourth disc priced at 1250, about 300 yuan lower than the market price. The seller is an individual player, upgraded and reborn, clearing all three SN levels. But once you get into the hardware, a hidden problem appears: after ten minutes of powering on, the fan produces a periodic 'buzz—buzz—' sound, which is a standard sign of bearing oil shortage. After running for another two months, it should be a complete issue. There are four tray holders, but only three remain, and the seller has been honest. When you boot up and enter the info center, the memory shows 8G—this machine comes standard with 4G, but the extra 4G is a generic tag added, so stability is questionable. If you run Docker too often, who knows when it will run blue one day.

hardware verification method, I summarized it in four points:

this machine didn't end up working out—not because the problem was serious, but because after hearing me mention the third bill, Da Liu gave up on his own. That debt is much harsher than a fan stand.

a bigger issue than its quality: how many more years can this machine survive system updates

buying second-hand Synology, the most easily overlooked aspect is the of the system's lifecycle. Synology will gradually stop DSM updates for older machines by model—new systems, new packages, security patches—once stopped, everything will be stopped. The DS918+ is a 2018 machine, and the major DSM version that can run has already run out. This is not a theoretical risk—the previous generation DSM 6.2 officially announced the end of support in December 2023, and security updates were effectively stopped in October 2024, leaving only a ten-month buffer period in between. Buying a machine running an older version of the system is like taking over a system that no longer fixes vulnerabilities. When I wrote about system updates NAS I specifically emphasized this principle: don't delay security patches; in the end, there's nothing left to delay.

Xianyu, there is a larger category of cheaper "Synology": four trays priced at five or six hundred yuan, with descriptions saying "perfect flashing" and "redeemed for use." This is Black Synology—a DSM for off-brand or self-built hardware flashing. When I previously wrote about how to choose hardware for Black Synology and how to install , I covered the entire route. It's not that it can't be played, and I personally recognize the value of the hassle, but comparing it to Synology second-hand prices is just a false proposition. Black Synology doesn't have a genuine SN, QuickConnect remotely is basically out of reach, and logging into the kit center is a hassle. The biggest flaw is that you can't just upgrade at will—once the official firmware is released, the boot can't hold up with the new kernel and becomes bricked, and you have to dismantle the machine and redo the boot disk.