Synology Calculator

Optimize your NAS storage with our professional Synology Calculator

What is the Synology Calculator?

The Synology Calculator is an essential utility for network-attached storage (NAS) owners and IT professionals. It allows users to simulate various drive configurations to determine how much actual storage space will be available after RAID overhead and data redundancy. Whether you are using traditional RAID 5 or Synology’s proprietary Synology Hybrid RAID (SHR), the Synology Calculator provides a visual and mathematical breakdown of your storage array.

A common misconception is that if you buy four 10TB drives, you will have 40TB of space. In reality, data protection mechanisms—which prevent data loss if a drive fails—consume a portion of that raw capacity. The Synology Calculator helps you avoid buying more or less storage than you actually need by providing precise estimates based on real-world file system math.

Synology Calculator Formula and Mathematical Explanation

The math behind the Synology Calculator depends heavily on the RAID type selected. While standard RAID levels (0, 1, 5, 6, 10) require identical drive sizes to be efficient, SHR allows for mixed drive sizes. Here is the logic the Synology Calculator uses:

• RAID 0: Sum of all drives (no protection).
• RAID 1: Capacity of the smallest drive (data is mirrored).
• RAID 5: (Number of drives – 1) × smallest drive capacity.
• RAID 6: (Number of drives – 2) × smallest drive capacity.
• SHR (1-drive fault tolerance): Total capacity minus the capacity of the single largest drive.
• SHR-2 (2-drive fault tolerance): Total capacity minus the capacity of the two largest drives.

Variables used in the Synology Calculator

Variable	Meaning	Unit	Typical Range
N	Number of Hard Drives	Count	1 – 24
C	Drive Capacity	Terabytes (TB)	1TB – 22TB
R	Redundancy Level	Drives	0, 1, or 2
U	Unused Space	TB	Variable

Practical Examples (Real-World Use Cases)

Example 1: The Home Media Server
A user has two 4TB drives and two 8TB drives. Using the Synology Calculator with SHR, the total raw capacity is 24TB. The calculator subtracts the largest drive (8TB) for protection. Result: 16TB available storage, 8TB protection. If they used RAID 5, they would be limited to 4TB per drive, resulting in only 12TB usable and 8TB unused (wasted).

Example 2: The Small Business Backup
A business uses six 12TB drives in RAID 6. The Synology Calculator calculates (6 – 2) * 12TB. Result: 48TB available, 24TB used for double-drive failure protection. This setup ensures the business remains online even if two drives fail simultaneously.

How to Use This Synology Calculator

Using our Synology Calculator is straightforward. Follow these steps to get an accurate storage estimation:

1. Select RAID Type: Choose between SHR, SHR-2, or standard RAID levels from the dropdown.
2. Enter Drive Sizes: Input the capacity of each hard drive in Terabytes (TB) in the slots provided.
3. Review Results: The Synology Calculator updates in real-time. The blue bar indicates usable space, green is for redundancy, and yellow indicates space that cannot be used due to RAID limitations.
4. Optimize: Experiment with different drive combinations to minimize the yellow “Unused” space.

Key Factors That Affect Synology Calculator Results

• File System Overhead: While the Synology Calculator provides raw usable capacity, the Btrfs or ext4 file system will take about 5-10% for metadata.
• Binary vs. Decimal: Manufacturers sell drives in decimal (1TB = 1,000GB), but Synology DSM calculates in binary (1TiB = 1,024GiB), leading to a ~7% discrepancy.
• Drive Mixing: SHR is the most flexible. In standard RAID 5, if you mix 4TB and 8TB drives, the 8TB drives will only act as 4TB drives.
• Fault Tolerance: Increasing protection (e.g., moving from SHR to SHR-2) decreases usable space but significantly reduces data loss risk.
• Number of Bays: Your NAS hardware limits how many drives the Synology Calculator can factor into a single volume.
• Expansion Capability: Adding larger drives later to an SHR array allows the Synology Calculator logic to reclaim previously “unused” space.

Frequently Asked Questions (FAQ)

1. What is the difference between RAID 5 and SHR in the Synology Calculator?

The Synology Calculator shows that RAID 5 requires all drives to be the same size to use 100% of the possible capacity, whereas SHR allows for mixed drive sizes by creating multiple smaller RAID arrays in the background.

2. Why does the Synology Calculator show “Unused” space?

Unused space occurs when you use mixed drive sizes in a configuration like RAID 5 or RAID 6. Because these RAID levels require equal chunks, the excess capacity on larger drives cannot be protected and thus becomes inaccessible.

3. Can I convert RAID 5 to SHR later?

No, you cannot convert between standard RAID and SHR without reformatting. You should use the Synology Calculator to decide your path before setting up the volume.

4. Is SHR slower than RAID 5?

The performance difference is negligible for most users. The Synology Calculator focuses on capacity, but in terms of speed, RAID 0 or 10 are the fastest.

5. How many drives can fail in SHR-2?

As the Synology Calculator results show for protection space, SHR-2 (and RAID 6) allows for up to two drive failures without data loss.

6. Does the Synology Calculator account for the 108TB volume limit?

No, this calculator shows total capacity. Some older Synology models have a 108TB limit per volume regardless of total drive capacity.

7. Why is my 10TB drive only showing 9.1TB in DSM?

This is the decimal-to-binary conversion mentioned earlier. The Synology Calculator uses the input values you provide, usually decimal TB.

8. Can I use different drive brands?

Yes, the Synology Calculator math works regardless of the brand, as long as the capacities are known.

Related Tools and Internal Resources

• NAS Selector Tool – Find the right Synology hardware for your needs.
• Drive Compatibility List – Ensure your HDDs/SSDs are supported.
• Advanced RAID Calculator – Deep dive into RAID rebuild times.
• 3-2-1 Backup Strategy Guide – Protecting your data beyond RAID.
• Surveillance Station Storage Calc – Calculate space for IP cameras.
• Deep Video Analytics Tool – Special requirements for DVA models.