SHR calculator
SHR is Synology's mixed-size RAID, and its party trick is using the spare space on bigger drives as soon as there are two of them to share it. Plug in your drives and flip between SHR and SHR-2 to see what the second parity drive costs you.
SHR · 4 drives · 44 TB raw
28TB
usable
≈ 25.5 TiB, which Windows calls “TB”
Survives 1 drive failing
- Usable
- 28 TB
- Protection
- 12 TB
- Unused
- 4 TB
- 4 TB on the biggest drive sits idle until another drive that size joins it.
Same drives, every layout
| Layout | Usable | Survives | Of raw |
|---|---|---|---|
| 28 TB | 1 | 64% | |
| 16 TB | 2 | 36% | |
| 44 TB | 0 | 100% | |
| 8 TB | 3 | 18% | |
| 24 TB | 1 | 55% | |
| 16 TB | 2 | 36% | |
| 16 TB | 1–2 | 36% | |
| 20 TB | 1–2 | 45% | |
| 24 TB | 1 | 55% | |
| 16 TB | 2 | 36% | |
| – | needs 5+ | ||
| 28 TB | 1 | 64% | |
| 16 TB | 2 | 36% | |
| 28 TB | 1 | 64% | |
| 16 TB | 2 | 36% | |
| 44 TB | 0 | 100% |
“Survives” counts the drives that can fail at once before the pool goes. Where it says 1–2, a second failure is only survivable if it lands in a different mirror pair.
SHR against RAID 5 on mixed drives
| Drives (TB) | SHR | SHR-2 | RAID 5 |
|---|---|---|---|
| 4 + 4 + 8 + 8 | 16 TB | 8 TB | 12 TB |
| 8 + 8 + 12 + 16 | 28 TB | 16 TB | 24 TB |
| 12 + 12 + 16 + 16 + 20 | 56 TB | 40 TB | 48 TB |
SHR-2 won't go below four drives. If you're shopping, the Synology boxes we list are Synology DS225+, Synology DS725+, Synology DS425+, Synology DS925+ and Synology DS1525+.