Synology Storage Calculator

Calculate your available capacity, data protection, and unused space for your Synology NAS using SHR, SHR-2, RAID 5, and more.

Used for Protection
4.00 TB

Unused Space
0.00 TB

Total Raw Capacity
16.00 TB

Synology Storage Calculator Capacity Summary

Metric	Value (TB)	Value (GB)	Percentage

What is a Synology Storage Calculator?

A synology storage calculator is a specialized utility designed to help NAS (Network Attached Storage) owners estimate the usable disk space in their device. Unlike simple hard drives where the advertised capacity is what you get, a Synology NAS uses RAID (Redundant Array of Independent Disks) configurations to protect your data from drive failures. This means a portion of your raw storage is “sacrificed” to create parity or mirror data.

Who should use this tool? Anyone planning to purchase a new Synology NAS, upgrading their existing hard drives, or looking to understand how Synology Hybrid RAID (SHR) handles mixed drive sizes. A common misconception is that adding an 8TB drive to a 4TB array immediately gives you 12TB of space. In reality, RAID math is more complex, and our synology storage calculator simplifies this logic for you.

Synology Storage Calculator Formula and Mathematical Explanation

The math behind the synology storage calculator varies significantly depending on the RAID level chosen. Synology is unique because of its proprietary SHR and SHR-2 levels, which are much more flexible than traditional RAID.

The Core Formulas:

• RAID 0: Available = Sum of all drives (No redundancy).
• RAID 1: Available = Size of the smallest drive (Assuming 2 drives).
• RAID 5: Available = (Number of Drives – 1) × Smallest Drive Size.
• RAID 6: Available = (Number of Drives – 2) × Smallest Drive Size.
• SHR: Available = Total Raw Capacity – Capacity of the Largest Drive (Simplified).
• SHR-2: Available = Total Raw Capacity – Capacity of the Two Largest Drives (Simplified).

Variable	Meaning	Unit	Typical Range
Raw Capacity	The sum of all physical disk labels	TB	2 TB – 200+ TB
Redundancy Space	Space reserved for data recovery	TB	Size of 1-2 drives
Btrfs/EXT4 Overhead	File system metadata requirement	%	3% – 5%

Practical Examples (Real-World Use Cases)

Example 1: The Home Media Server

User has 4 drives: two 4TB drives and two 8TB drives. Using a standard synology storage calculator with RAID 5, the system would treat all drives as 4TB, resulting in (4-1) × 4 = 12TB available. However, using SHR, the calculation allows the extra space on the 8TB drives to be utilized. SHR would provide 16TB of usable space with 1-drive redundancy.

Example 2: Small Business Office

A business uses six 12TB drives in RAID 6 for high availability. The synology storage calculator logic dictates: (6 – 2) × 12TB = 48TB available. 24TB is dedicated to protection, ensuring the office stays online even if two drives fail simultaneously.

How to Use This Synology Storage Calculator

Follow these steps to get an accurate estimation of your NAS capacity:

1. Select RAID Type: Choose from SHR, RAID 5, etc. If you are unsure, SHR is the recommended default for Synology users.
2. Input Drive Sizes: Enter the capacity of each drive currently in your NAS or the drives you plan to buy.
3. Review Results: The primary result shows “Available Storage.” Below that, check the “Used for Protection” value.
4. Check the Chart: The visual breakdown helps you see how much of your investment is actually storing data versus protecting it.

Key Factors That Affect Synology Storage Calculator Results

1. Disk Manufacturer Rating: HDD makers use decimal (1TB = 1,000GB) while Synology uses binary (1TiB = 1,024GiB). This results in an immediate ~7% reduction in perceived space.
2. RAID Redundancy: The more drives you “lose” to redundancy (like RAID 6 or SHR-2), the safer your data is, but the lower your usable capacity.
3. Mixed Drive Sizes: Traditional RAID levels (5, 6, 10) base capacity on the smallest drive. SHR allows you to mix sizes more effectively.
4. File System Overhead: Btrfs and EXT4 require space for metadata and indexing, usually reducing usable space by another 2-5%.
5. Hot Spares: If you designate a drive as a “Hot Spare,” it is excluded from the synology storage calculator available capacity.
6. System Partition: Synology reserves a small portion of every drive for the DSM operating system itself.

Frequently Asked Questions (FAQ)

1. Is SHR better than RAID 5?

For most users, yes. SHR allows for easier expansion and better utilization of mixed drive sizes compared to traditional RAID 5.

2. Why does my 10TB drive only show 9.1TB in DSM?

This is due to the difference between Terabytes (decimal) used by manufacturers and Tebibytes (binary) used by the operating system.

3. Can I change RAID levels later?

Yes, Synology allows migrating from basic to RAID 1, or RAID 1 to RAID 5, but you generally cannot go “down” in redundancy without wiping the volume.

4. What is the maximum volume size?

Most modern Synology units support 108TB or 200TB volumes, depending on the CPU architecture (32-bit vs 64-bit).

5. How does SHR-2 differ from RAID 6?

Both allow for two drive failures. SHR-2 is Synology’s flexible version that handles mixed drive sizes better than standard RAID 6.

6. Should I use RAID 0?

Only if you don’t care about the data. If one drive fails in RAID 0, all data on the entire array is lost.

7. Does adding an SSD cache increase storage capacity?

No, an SSD cache only improves read/write speeds; it does not add to the available storage calculated by the synology storage calculator.

8. Can I use different speed drives (5400 RPM vs 7200 RPM)?

Yes, but the array will generally perform at the speed of the slowest drive in the pool.