Compatibility / Synology / DS1821+

Compatible Hard Drives for the Synology DS1821+

Synology's list read 19 August 2026. Prices live.

Drives that work in the DS1821+, cheapest per terabyte

These are internal SATA hard drives in stock now. They are not on Synology's list for the DS1821+ - nothing third-party is - and on this machine that does not stop them working. Each row says so explicitly rather than leaving the cell blank.

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What “not on the list” means on this machine

It is worth being precise here, because the same phrase means two completely different things on two different Synology machines.

On a Value or J-series machine launched in 2025 or later, an unlisted hard drive cannot create a storage pool. It is not a warning that can be dismissed; the software declines. And because Synology's current list contains no third-party hard drives at all, the practical effect on those machines is that only Synology-branded drives can build a pool.

The DS1821+ is not in that group. Its list is Synology-only, exactly like the newer machines, but the restriction that makes that fact bite does not apply to it. A drive from the table above will initialise, build a pool and run. The absence tells you Synology has not validated the drive against this model, which is a real thing to know and a much smaller thing than being blocked.

For models of this era the boundary follows no year or series rule we can verify; this page records what the DS1821+'s list actually shows. We checked machines on both sides of that boundary and they do not line up: two machines of the same generation, one Value and one Plus, behaved differently from each other, and older machines still carry long third-party lists that newer ones lost. We will not print a cutoff year we cannot defend. The drive policy page carries the rule as Synology states it, per series, with dates.

The DS1821+ list was read with Synology's own model filter, www.synology.com, read 19 August 2026. We record what the list said on that date; we do not re-read it when you load this page.

What the DS1821+'s list size tells you

At 47 listed drives the DS1821+ matches the DS1621+ and exceeds the desktop machines by four. It is also the machine where the arithmetic of the brand premium is least forgiving: eight bays means the per-terabyte gap is multiplied eight times over, and on a full build that turns a preference into a four-figure decision.

Across the ten Synology machines we measured, the counts run from 4 to 47. If a compatibility list described what a machine could physically accept, that range would make no sense - the hardware differences between these units are nothing like that dramatic. What the range actually tracks is how recently each machine sat in Synology's current line-up, which is a fact about testing budgets rather than about engineering.

Synology's own drives for the DS1821+

These are the drives that carry the strongest claim available on this page: Synology lists them, so they are vendor-listed rather than merely fitting. If you want the machine and the media supported by one company, this is what that looks like at today's prices.

What the brand costs, measured

At 16TB on SATA, Synology's own drive is $63.21 per terabyte against $42.78 for the cheapest qualifying alternative - a premium of +47.8%, computed from live listings and matched interface to interface.

The matching is not a technicality. Compared against a SATA peer instead of a SAS one, Synology's 12TB SAS drive reads at a premium near 97% - but that number measures the gap between SAS and SATA, not the gap between Synology and everyone else. Any percentage on this site that describes a difference is matched like for like, and an external USB drive is never used as the comparison for an internal one.

Choosing between them

There is a defensible case for either column, and the honest version of it is short.

Synology's drives buy you validation and a single support relationship. When a drive misbehaves in a Synology chassis with Synology media, nobody can point at anybody else, and DSM surfaces firmware and health data for its own drives that it does not always get from third-party models. For a business machine that has to be somebody's responsibility, that is worth real money.

Third-party NAS drives buy you choice and a lower price per terabyte, and on the DS1821+ they cost you nothing in function. The drives in the first table are the same models that have run in NAS units for years. What you are giving up is a line in a vendor's spreadsheet.

As a reference point, the cheapest terabyte on this page today is the MDD 20TB SATA 7200RPM NAS at $25.00 per terabyte, $499.99 for 20TB. Whether that is the right drive for your machine depends on how hard you intend to work it - a drive can be the cheapest per terabyte and still be wrong for an array that never spins down. Our CMR or SMR resolver is the first check worth running on any candidate.

What this page does not tell you

Two things, deliberately. We do not state a bay count or a maximum capacity for the DS1821+, because we have not sourced either from Synology. Both circulate widely and both are frequently wrong or out of date, and a wrong ceiling either costs you a drive you could have used or sells you one that will not work.

We also do not tell you when the DS1821+ launched. The 2025 boundary is the thing that decides whether the restriction applies, so a launch year is load-bearing here, and we would rather point you at Synology's own page for that machine than assert a date from memory. What this page does hold is what Synology's list said on a specific day, and the date is printed beside it.

Other Synology machines

The counts differ more than you might expect - from 4 drives on one machine to 47 on another - which is itself the clearest evidence that Synology maintains these lists per model rather than publishing one list for everything. See the compatibility hub for how the other manufacturers handle the same question.