How much storage fits in the Synology DiskStation DS1525+?
By Devin Chua · Data checked by Owen Nakamura · Updated · Prices checked The Synology DiskStation DS1525+ takes 5 drives, up to 120 TB raw, but usable is the number that matters: 5 × 8 TB in SHR gives 29.10 TiB for about CA$2,860 in drives, and it survives 1 drive failing. The gap from raw capacity is parity, and SHR lets you grow with mixed drive sizes.
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Want to know whether the DS1525+ fits your actual storage plan? Open the NAS Builder with this model weighted.
Usable space in the DS1525+, by drive size
All 5 bays filled with equal drives in SHR, the DS1525+’s sensible default. Usable TiB is what the NAS reports; TB is the drive maker’s unit.
| Drive size | Raw | Usable (TB) | Usable (TiB) | Drive failures survived |
|---|---|---|---|---|
| 5 × 4 TB | 20 TB | 16 TB | 14.55 TiB | 1 |
| 5 × 8 TB | 40 TB | 32 TB | 29.10 TiB | 1 |
| 5 × 12 TB | 60 TB | 48 TB | 43.66 TiB | 1 |
| 5 × 16 TB | 80 TB | 64 TB | 58.21 TiB | 1 |
| 5 × 20 TB | 100 TB | 80 TB | 72.76 TiB | 1 |
| 5 × 24 TB | 120 TB | 96 TB | 87.31 TiB | 1 |
How much space you actually need
Start from what you store today, not from the drive sizes. As rough guides: a 24-megapixel RAW photo is about 25 to 30 MB, a phone photo 3 to 5 MB, and an hour of 4K phone video around 20 GB; check a folder of your own files for real numbers. Add the growth you expect over the next three to five years, then keep about 20 percent free so the pool does not run full.
Then plan the backup copy. RAID keeps the DS1525+ running through a drive failure; it does not protect against deletion, ransomware, theft or fire. Size a second copy (an external drive, a second NAS or a cloud plan) for the data you cannot replace, which is often far less than the array.
For your own mix of drive sizes and RAID types, use the DS1525+ capacity calculator. For drives that fit and their current Amazon.ca prices, see the best drives for the DS1525+.
A worked configuration for the DS1525+
WD Red Pro or Seagate IronWolf Pro in every bay is the recommendation for the DS1525+. At 5 × 8 TB in SHR, the DS1525+ lands 29.10 TiB usable for about CA$2,860 in drives, gives up 8 TB to parity, and survives 1 drive failing. Step the same 5 bays of the DS1525+ up to 16 TB drives and it holds roughly twice that, at the CA$/TB the live table above shows.
SHR or RAID 6 in the DS1525+?
With 5 bays the DS1525+ gives a real choice. In SHR it keeps 29.10 TiB of the 5 × 8 TB and survives one failure; RAID 6 spends one more drive for two. The trade tips with large drives: after a failure the DS1525+ must read every surviving drive in full to rebuild, which on 20 TB drives runs the better part of a day under peak load. So from 16 TB per drive up, RAID 6 is the calmer choice in the DS1525+, and SHR-2 gives the same protection while still using mixed drive sizes.
One rule holds on every NAS, the DS1525+ included: use CMR drives, not SMR. SMR drives rewrite overlapping tracks and collapse during a RAID rebuild, dragging a repair from hours into days.
Drive policy: Since DSM 7.3 (8 October 2025) the DS1525+ accepts third-party hard drives and 2.5-inch SATA SSDs for new storage pools; only M.2 NVMe still has to come from Synology's list. The DS1525+’s full compatibility rules.
Keep calculating
To see how much capacity is left after parity, the DS1525+ capacity calculator is preset to its 5 bays and RAID types. For the DS1525+, the wider basics of choosing a drive are in the buying guides, and CMR versus SMR explains why SMR drives do not belong in a RAID array. Wondering what the DS1525+ can actually do: Plex, Immich, Docker, VMs? See what the DS1525+ can run.
Frequently asked questions
What is the maximum storage in the DS1525+?
5 drives, up to 120 TB raw per the manufacturer. 5 × 24 TB, per the manufacturer
How much of the DS1525+ is actually usable?
In the DS1525+, 5 × 8 TB in SHR yields about 29.10 TiB: that is 32 TB in drive-maker terms, with 8 TB to parity. It shows less than the label because it counts in powers of two.
Can I fit larger drives in the DS1525+ later?
Yes, and with SHR it is easy: swap the DS1525+'s drives for larger ones one at a time, and the gain arrives once the second-largest drive is also larger.
Can I put third-party drives in the DS1525+?
Yes. Since DSM 7.3 (8 October 2025) the DS1525+ accepts third-party hard drives and 2.5-inch SATA SSDs for new storage pools; only M.2 NVMe still has to come from Synology's list.
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)