When planning a Synology NAS (Network Attached Storage) setup, one of the most common concerns is understanding how much usable storage space will actually be available. Hard drives may have large advertised capacities, but due to RAID configurations, redundancy, and disk overhead, the final usable space is often different.
Synology Space Calculator
The Synology Space Calculator is an online tool by Synology that allows users to:
- Estimate usable NAS storage capacity.
- Simulate different RAID levels (RAID 0, RAID 1, RAID 5, RAID 6, RAID 10, SHR).
- Check data redundancy and number of drive failures tolerated.
- Plan storage before purchasing new hard drives.
- Optimize cost vs efficiency when setting up a Synology NAS.
It is especially useful for beginners and professionals who want to ensure they are getting the best balance between performance, storage, and data protection.
🔹 How Does the Synology Space Calculator Work?
The calculator applies RAID formulas to determine usable space depending on disk numbers, sizes, and redundancy requirements.
RAID Storage Formulas:
- RAID 0 (Striping):
Usable Space = Sum of all drives
No redundancy. - RAID 1 (Mirroring):
Usable Space = Size of the smallest drive
50% efficiency for 2 drives. - RAID 5:
Usable Space = (Number of drives – 1) × Smallest drive size
Can tolerate 1 drive failure. - RAID 6:
Usable Space = (Number of drives – 2) × Smallest drive size
Can tolerate 2 drive failures. - RAID 10 (1+0):
Usable Space = 50% of total raw capacity
Combines speed and redundancy. - SHR (Synology Hybrid RAID):
Optimizes space when using different drive sizes while keeping redundancy.
🔹 How to Use the Synology Space Calculator
- Choose Number of Drives – Select the number of disks in your NAS.
- Enter Drive Sizes – Input capacity of each HDD/SSD.
- Select RAID/SHR Type – Choose RAID 0, 1, 5, 6, 10, or SHR.
- View Results – The calculator will display:
- Total raw capacity
- Usable storage space
- Data protection level (number of drives that can fail)
- Storage efficiency (%)
- Adjust Scenarios – Try different RAID options to see best balance.
🔹 Example Calculations
Example 1: 4 × 4TB drives in RAID 5
- Raw Capacity = 16TB
- Usable Capacity = (4 – 1) × 4TB = 12TB
- Protection = 1 drive
Example 2: 6 × 10TB drives in RAID 6
- Raw Capacity = 60TB
- Usable Capacity = (6 – 2) × 10TB = 40TB
- Protection = 2 drives
Example 3: 3 × 6TB + 2 × 8TB drives in SHR
- Raw Capacity = 34TB
- Usable Capacity ≈ 24TB (depends on SHR optimization)
- Protection = 1 drive
🔹 Benefits of Using the Synology Space Calculator
✔ Prevents overestimating usable space
✔ Compares RAID vs SHR before buying drives
✔ Helps optimize budget and storage investment
✔ Guides on best redundancy setup for safety
✔ Easy to use for both beginners and IT professionals
✔ Saves time when planning home or business NAS
🔹 Things to Keep in Mind
- Usable storage is always less than raw capacity due to RAID overhead.
- RAID provides redundancy but is not a backup. Always keep external/cloud backups.
- SHR is recommended when mixing drive sizes.
- Larger drives mean longer rebuild times in case of failure.
- SSDs offer speed benefits but come at higher cost.
🔹 Frequently Asked Questions (FAQs)
Q1. What is the Synology Space Calculator?
It’s a tool that estimates usable NAS capacity based on drives and RAID type.
Q2. Can I use it with different drive sizes?
Yes, especially with SHR which optimizes mismatched drives.
Q3. Does it include parity calculation?
Yes, it accounts for parity overhead in RAID 5 and 6.
Q4. Can it calculate rebuild time?
No, it only estimates capacity, not rebuild duration.
Q5. Does RAID 0 provide protection?
No, RAID 0 has zero redundancy.
Q6. Is RAID 1 space efficient?
Not very; it uses 50% capacity for redundancy.
Q7. What’s better: RAID 5 or RAID 6?
RAID 5 is more space-efficient, RAID 6 offers stronger redundancy.
Q8. Can I simulate SHR-2 in the calculator?
Yes, SHR-2 provides protection against 2 drive failures.
Q9. Does it work for SSDs?
Yes, you can enter SSD sizes as well.
Q10. Is usable capacity same as raw capacity?
No, redundancy reduces usable space.
Q11. Can I add drives later?
Yes, SHR allows expansion with larger or additional drives.
Q12. Is RAID 10 supported in the calculator?
Yes, it shows RAID 10 usable space and redundancy.
Q13. Is RAID a backup solution?
No, RAID protects against drive failure but not accidental deletion.
Q14. Can the calculator show efficiency percentage?
Yes, it shows usable capacity as a percentage of raw space.
Q15. Does it cost anything to use?
No, the Synology Space Calculator is free.
Q16. What happens if one drive fails in RAID 5?
Data remains safe, but the system runs in degraded mode until replaced.
Q17. Is SHR recommended for beginners?
Yes, SHR is easier to use and more flexible.
Q18. Can I use it for enterprise setups?
Yes, businesses also use it for capacity planning.
Q19. Does it calculate hot spares?
Yes, you can assign hot spare drives.
Q20. Is RAID 10 good for speed?
Yes, RAID 10 combines striping and mirroring for fast and secure storage.
🔹 Conclusion
The Synology Space Calculator is an invaluable tool for anyone setting up a NAS system. By accurately simulating drive combinations and RAID levels, it removes the guesswork from storage planning. Whether you’re a home user managing media files or a business ensuring data safety, this tool helps you strike the right balance between capacity, redundancy, and efficiency.