When building a Synology NAS (Network Attached Storage) system, one of the biggest challenges users face is estimating how much usable storage they’ll get from their hard drives. Factors like RAID configuration, disk size, redundancy, and number of drives all affect the final storage capacity. The Synology Disk Calculator is a powerful tool that simplifies this process.
Synology Disk Calculator
The Synology Disk Calculator is an online tool provided by Synology that allows users to:
- Calculate usable storage capacity based on number of disks.
- Compare different RAID configurations (RAID 0, RAID 1, RAID 5, RAID 6, RAID 10, SHR, etc.).
- Plan data protection and redundancy.
- Estimate storage waste due to parity and mirroring.
- Simulate combinations of HDDs and SSDs in a NAS setup.
It’s especially helpful when choosing between Synology Hybrid RAID (SHR) and traditional RAID levels.
🔹 How Does the Synology Disk Calculator Work?
The calculator uses RAID storage formulas and redundancy rules to determine the usable space.
RAID Capacity Formulas:
- RAID 0 (Striping):
Usable capacity = Sum of all drives
No redundancy. - RAID 1 (Mirroring):
Usable capacity = Size of smallest drive
High redundancy, good for 2 disks. - RAID 5:
Usable capacity = (Number of drives – 1) × Smallest drive size
Tolerates 1 drive failure. - RAID 6:
Usable capacity = (Number of drives – 2) × Smallest drive size
Tolerates 2 drive failures. - RAID 10 (1+0):
Usable capacity = 50% of total drives
Combines mirroring and striping. - Synology Hybrid RAID (SHR):
Optimizes space with mixed drive sizes while keeping redundancy.
🔹 How to Use the Synology Disk Calculator
- Select Number of Drives – Choose how many disks you plan to install.
- Enter Drive Size – Input size of each HDD/SSD (e.g., 4TB, 8TB, 12TB).
- Select RAID/SHR Type – Pick a storage configuration.
- Check Results – The tool shows:
- Usable capacity
- Redundancy level
- Drive failure tolerance
- Storage loss due to parity/mirroring
- Adjust Settings – Try different combinations to see best efficiency.
🔹 Example Calculations
Example 1: 4 × 4TB drives in RAID 5
- Total raw capacity = 16TB
- Usable capacity = (4 – 1) × 4TB = 12TB
- Redundancy = 1 drive tolerance
Example 2: 6 × 8TB drives in RAID 6
- Total raw capacity = 48TB
- Usable capacity = (6 – 2) × 8TB = 32TB
- Redundancy = 2 drives tolerance
Example 3: 3 × 6TB + 2 × 10TB drives in SHR
- SHR adjusts different disk sizes
- Usable capacity ≈ 28TB
- Redundancy = 1 drive tolerance
🔹 Benefits of Using the Synology Disk Calculator
✔ Avoids storage miscalculations
✔ Shows best RAID option for efficiency and safety
✔ Helps budget planning for new drives
✔ Useful for home media servers and business storage systems
✔ Compares SHR vs RAID effectively
✔ Guides toward optimal redundancy
🔹 Things to Consider When Planning Storage
- Larger drives mean longer rebuild times after a failure.
- RAID is not a backup – always keep external/cloud backups.
- SHR is recommended for mixed drive sizes.
- RAID 5/6 is efficient for multiple drives, but RAID 10 offers faster performance.
- SSDs improve performance but are costlier.
🔹 Frequently Asked Questions (FAQs)
Q1. What is the Synology Disk Calculator used for?
It helps estimate usable storage capacity based on RAID and drive setup.
Q2. Does the calculator work with different drive sizes?
Yes, especially with Synology Hybrid RAID (SHR).
Q3. Can it show RAID rebuild time?
No, it only calculates capacity, not rebuild duration.
Q4. Is RAID 0 recommended for NAS?
No, RAID 0 offers no redundancy and is risky for NAS storage.
Q5. What’s the main difference between SHR and RAID?
SHR allows mixing different drive sizes, RAID typically requires equal-sized drives.
Q6. Can I calculate with SSDs?
Yes, the calculator supports SSDs as well.
Q7. How much storage do I lose with RAID 1?
You lose 50% capacity because all data is mirrored.
Q8. Is RAID 6 better than RAID 5?
RAID 6 offers more redundancy (2 drives can fail), but it reduces usable capacity further.
Q9. Can SHR protect against multiple drive failures?
Yes, SHR-2 provides protection against 2 drive failures.
Q10. Is the calculator available offline?
No, it’s an online tool by Synology.
Q11. Does it work for external drives?
No, only for NAS-configured drives.
Q12. Can I use it to plan backups?
It’s for storage calculation, not backup scheduling.
Q13. Does the calculator include hot spares?
Yes, you can select drives as hot spares in the setup.
Q14. What happens if I add new drives later?
In SHR, storage expands automatically; RAID requires equal-sized drives.
Q15. Is RAID 10 good for video editing?
Yes, RAID 10 offers high performance with redundancy.
Q16. Does Synology recommend SHR for beginners?
Yes, it’s simpler and more flexible for mixed drives.
Q17. Can the calculator show parity overhead?
Yes, it shows how much space is reserved for redundancy.
Q18. Is usable space same as raw capacity?
No, usable space is always less due to parity and redundancy.
Q19. Can I switch from RAID 5 to SHR later?
Yes, but it may require rebuilding and migration.
Q20. Does the calculator cost anything?
No, it’s free to use on Synology’s official site.
🔹 Conclusion
The Synology Disk Calculator is an essential planning tool for anyone building a NAS system. It takes the guesswork out of RAID configurations by showing usable storage capacity, redundancy levels, and efficiency. Whether you’re setting up a home media server, small office NAS, or enterprise storage solution, this calculator ensures you make smart decisions before buying drives.