Synology DiskStation DS925+: capacity calculator
By Devin Chua · Data checked by Owen Nakamura · Updated In the Synology DiskStation DS925+ with 4 × 8 TB in SHR you keep 21.83 TiB usable (24 TB in drive-maker terms), surviving 1 drive failing. The calculator below is preset to the 4 bays and the RAID types DSM 7.3 or newer actually offers on this model (including SHR, which uses mixed drive sizes), with the cost to fill in Canadian dollars from live Amazon.ca prices.
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Preset for the DS925+: 4 bays, and only the RAID types this model actually supports.
SHR (Synology Hybrid RAID)
That is 24 TB the way drive makers label capacity. Your NAS shows you the smaller number because it counts in powers of two.
Drives: from CA$2,016 for 4 × 8 TB (CA$63.01/TB overall)
What to know about the DS925+
The model the whole drive debate revolves around. Since DSM 7.3 you can fit ordinary NAS drives again, and with SHR the DS925+ makes good use of mixed drive sizes. Do not overlook: unlike the DS923+ it has no slot for a 10-gigabit card, but it ships with two 2.5-gigabit ports.
The DS925+ at a glance
| Bays | 4 × 3.5-inch SATA and 2.5-inch SATA SSD |
|---|---|
| Maximum raw capacity | 96 TB 4 × 24 TB, per the manufacturer |
| Processor | AMD Ryzen V1500B (4 cores, 8 threads) |
| Memory | 4 GB stock, DDR4 ECC SO-DIMM (2 slots) 32 GB official, ECC |
| M.2 NVMe | 2 slots 2 × M.2 NVMe. Note: for BOTH an NVMe cache and an NVMe storage pool, Synology still requires a drive from its own compatibility list. That is the remaining lock. |
| Network | 2 × 2.5GbE |
| RAID types | SHR, SHR-2, Basic, JBOD, RAID 0, RAID 1, RAID 5, RAID 6, RAID 10 |
| Third-party drives | with a caveat Partly open, and this is the key news. On 16 April 2025 Synology announced that the 2025 Plus models would only create a storage pool with listed drives. With DSM 7.3 (version 7.3-81180, released 8 October 2025) Synology reversed that lock for hard drives and 2.5-inch SATA SSDs: Seagate IronWolf and WD Red Plus now install, initialize, pool and monitor normally. Only M.2 NVMe still requires a listed drive. |
SHR is the real reason to buy the DS925+
SHR subtracts only the largest drive from the total, instead of sizing to the smallest like RAID 5. On the DS925+ that means you can start with two drives, add a larger one later, and actually use the gain. UGREEN and QNAP have no equivalent, and with mismatched drives that freedom is quickly worth several hundred dollars. With equal-size drives SHR is arithmetically the same as RAID 5, so there it is simply preference.
RAID 5 or RAID 6 across the DS925+'s 4 bays?
With 4 bays the DS925+ gives you the choice. RAID 5 (or SHR) leaves 3 of 4 drives as usable capacity and survives one failure; RAID 6 spends one more drive for two. The rule of thumb: from 16 TB drives up, the rebuild after a failure runs so long — easily a full day — that a second failure in that window stops being theoretical. That is when RAID 6 earns its cost on the DS925+.
Which drives belong in the DS925+?
CMR NAS drives rated for 24/7 use — Seagate IronWolf, WD Red Plus, Toshiba N300 or their Pro variants. Our drive picks for the DS925+ with live prices show which of those currently offers the best capacity per dollar. If you are working back from a target capacity instead, the drive-count calculator works out how many drives you need.
Frequently asked questions
How much storage is left in the DS925+ with 4 × 8 TB?
About 21.83 TiB usable — 24 TB in drive-maker terms — computed in SHR, the sensible default for this model. It survives 1 drive failing. The gap from the 32 TB raw goes to parity.
Which RAID types does the DS925+ support?
DSM 7.3 or newer offers SHR, SHR-2, Basic, JBOD, RAID 0, RAID 1, RAID 5, RAID 6, RAID 10 on the DS925+. SHR is the one that matters: it lets the DS925+ use mixed drive sizes instead of leveling every drive down to the smallest.
Can I put third-party drives in the DS925+?
Partly open, and this is the key news. On 16 April 2025 Synology announced that the 2025 Plus models would only create a storage pool with listed drives. With DSM 7.3 (version 7.3-81180, released 8 October 2025) Synology reversed that lock for hard drives and 2.5-inch SATA SSDs: Seagate IronWolf and WD Red Plus now install, initialize, pool and monitor normally. Only M.2 NVMe still requires a listed drive.
How much memory does the DS925+ take?
It ships with 4 GB (DDR4 ECC SO-DIMM (2 slots)). 32 GB official, ECC There are 2 slots.
Why does my NAS show less than the calculator says?
Because the maker and the OS count differently. A drive maker calls one trillion bytes a TB; the NAS counts in powers of two and calls that a TiB — about 9 percent less. That is why this calculator leads with the TiB figure: it is the number you will read off the screen.
Devin Chua works out which drives, RAM and NVMe cache fit which NAS model at nasdrives.ca, and what the RAID choice means for usable capacity, checked against what is in stock on Amazon.ca.
Data checked by Owen Nakamura, Technical editor (data checking)