Synology DiskStation DS423+: capacity calculator
By Devin Chua · Data checked by Owen Nakamura · Updated In the Synology DiskStation DS423+ 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.x 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 DS423+: 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 DS423+
The price entry with four bays and SHR. The Celeron J4125 can transcode Plex with hardware acceleration, but the 2 GB of RAM out of the box is tight: the single free SO-DIMM is effectively mandatory and caps you at 6 GB.
The DS423+ at a glance
| Bays | 4 × 3.5-inch SATA and 2.5-inch SATA SSD |
|---|---|
| Maximum raw capacity | 96 TB 4 × 24 TB: the largest drive on Synology's list for this model. The often-quoted 108 TB is the maximum volume size, not the sum of drives. |
| Processor | Intel Celeron J4125 (4 cores) |
| Memory | 2 GB stock, DDR4 SO-DIMM, no ECC (2 GB soldered plus 1 slot) 6 GB official (2 GB fixed plus a 4 GB module). In practice a 16 GB module runs (giving 18 GB); Synology does not endorse it. |
| M.2 NVMe | 2 slots 2 × M.2 NVMe for cache; an NVMe storage pool requires a Synology drive |
| Network | 2 × 1GbE |
| RAID types | SHR, SHR-2, Basic, JBOD, RAID 0, RAID 1, RAID 5, RAID 6, RAID 10 |
| Third-party drives | unrestricted Open. The 2025 restriction does not apply retroactively; every NAS drive works. |
SHR is the real reason to buy the DS423+
SHR subtracts only the largest drive from the total, instead of sizing to the smallest like RAID 5. On the DS423+ 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 DS423+'s 4 bays?
With 4 bays the DS423+ 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 DS423+.
Which drives belong in the DS423+?
CMR NAS drives rated for 24/7 use — Seagate IronWolf, WD Red Plus, Toshiba N300 or their Pro variants. Our drive picks for the DS423+ 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 DS423+ 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 DS423+ support?
DSM 7.x offers SHR, SHR-2, Basic, JBOD, RAID 0, RAID 1, RAID 5, RAID 6, RAID 10 on the DS423+. SHR is the one that matters: it lets the DS423+ use mixed drive sizes instead of leveling every drive down to the smallest.
Can I put third-party drives in the DS423+?
Open. The 2025 restriction does not apply retroactively; every NAS drive works.
How much memory does the DS423+ take?
It ships with 2 GB (DDR4 SO-DIMM, no ECC (2 GB soldered plus 1 slot)). 6 GB official (2 GB fixed plus a 4 GB module). In practice a 16 GB module runs (giving 18 GB); Synology does not endorse it. There is one slot.
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)