Synology RAID Calculator
Plan your NAS storage capacity and redundancy levels with precision.
Select the RAID configuration for your Synology NAS.
Invalid configuration for selected RAID type.
Formula: RAID 1 uses the capacity of the smallest drive for data and mirrors it.
What is a Synology RAID Calculator?
A Synology RAID Calculator is an essential tool for anyone planning to deploy a Network Attached Storage (NAS) system. It allows users to estimate how much actual data storage they will have after accounting for redundancy and system overhead. Unlike standard hard drives connected to a PC, a Synology NAS uses Redundant Array of Independent Disks (RAID) technology to protect data against drive failures.
Who should use it? System administrators, home media enthusiasts, and small business owners use the Synology RAID Calculator to decide which hard drives to purchase and which RAID level balances their need for speed, capacity, and data safety. A common misconception is that if you buy four 10TB drives, you will have 40TB of space. In reality, depending on your RAID choice, you might only have 20TB or 30TB available.
Synology RAID Calculator Formula and Mathematical Explanation
The mathematical logic behind the Synology RAID Calculator varies significantly based on the RAID level chosen. Synology also offers a proprietary system called SHR (Synology Hybrid RAID), which uses a more complex spanning algorithm to maximize space when using mixed drive sizes.
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| N | Number of Drives | Count | 1 – 24 |
| Smin | Smallest Drive Capacity | Terabytes (TB) | 1 – 22 TB |
| Stotal | Sum of all Drive Capacities | Terabytes (TB) | Varies |
| R | Redundancy Overhead | Terabytes (TB) | 1x to 2x Smax |
Step-by-Step Derivation
1. RAID 5: The formula is (N – 1) * Smin. This assumes all drives are the same size. If they aren't, the extra space on larger drives is wasted.
2. SHR: Synology Hybrid RAID calculates available space by taking the total capacity and subtracting the capacity of the largest drive (for 1-drive redundancy). This allows for much better utilization of mixed-size drives.
Practical Examples (Real-World Use Cases)
Example 1: The Small Business Setup
A business uses four 8TB drives in RAID 6. Using the Synology RAID Calculator, we apply the formula (N-2) * S. Here, (4-2) * 8 = 16TB. The business has 16TB of usable space and can survive the simultaneous failure of any two drives.
Example 2: The Home Media Server (Mixed Drives)
A user has two 4TB drives and two 8TB drives. In a traditional RAID 5, the system would treat all drives as 4TB, resulting in (4-1) * 4 = 12TB usable, with 8TB wasted. By using the Synology RAID Calculator for SHR, the result is (4+4+8+8) – 8 = 16TB usable. SHR effectively gains 4TB of extra space.
How to Use This Synology RAID Calculator
Follow these steps to plan your storage:
- Select RAID Type: Choose from SHR, RAID 5, RAID 6, etc., based on your redundancy needs.
- Input Drive Sizes: Enter the capacity of each drive in Terabytes. If a slot is empty, leave it at 0.
- Review Results: The Synology RAID Calculator instantly updates the "Available Capacity" and "Protection" metrics.
- Analyze the Chart: The visual bar shows the ratio of usable space to protection overhead.
Key Factors That Affect Synology RAID Calculator Results
- Drive Count: Certain RAID levels require a minimum number of drives (e.g., RAID 5 needs 3, RAID 6 needs 4).
- Binary vs. Decimal: Drive manufacturers define 1TB as 1,000,000,000,000 bytes, but DSM (Synology's OS) uses binary (TiB). This calculator uses decimal TB for planning purposes.
- Btrfs Metadata: A small portion of space is reserved for the Btrfs file system metadata and system partitions.
- SHR Flexibility: SHR allows you to add larger drives later and expand the array, a factor the Synology RAID Calculator highlights through "Unused Space" indicators.
- RAID 10 Efficiency: RAID 10 provides high performance but always cuts total capacity by 50%.
- Hot Spares: If you designate a drive as a hot spare, it is not included in the usable capacity calculation.
Frequently Asked Questions (FAQ)
1. Why is my available space lower than the calculator says?
Synology reserves about 4-5% of the total capacity for system partitions and the Btrfs file system metadata. Also, check if you are confusing TB (decimal) with TiB (binary).
2. Can I change RAID levels later?
Yes, Synology allows migration from RAID 1 to RAID 5, or RAID 5 to RAID 6, but you cannot go backwards without deleting the volume.
3. Is SHR better than RAID 5?
For most users, yes. SHR offers the same redundancy as RAID 5 but provides more flexibility when mixing drive sizes. Learn more in our Synology SHR Explained guide.
4. How many drives can fail in RAID 6?
RAID 6 can survive the failure of up to two drives simultaneously without data loss. This is compared in our RAID 5 vs RAID 6 Comparison.
5. Does the calculator account for SSD Cache?
No, SSD Cache does not increase storage capacity; it only improves I/O performance. See SSD Cache Benefits for details.
6. What happens to "Unused Space"?
In the Synology RAID Calculator, unused space occurs when drive sizes are incompatible with the RAID level's math. In SHR, this space can often be reclaimed by adding another large drive.
7. Is RAID a backup?
No. RAID protects against hardware failure, not data corruption or accidental deletion. Always follow Data Backup Strategies.
8. Which drives are most reliable for RAID?
NAS-rated drives like WD Red or Seagate IronWolf are recommended. Check our Hard Drive Reliability report.
Related Tools and Internal Resources
- NAS Storage Guide – A comprehensive manual for beginners setting up their first Synology.
- RAID 5 vs RAID 6 Comparison – Detailed breakdown of parity-based storage.
- Synology SHR Explained – Why Synology's hybrid RAID is a game changer.
- Data Backup Strategies – How to implement the 3-2-1 backup rule.
- Hard Drive Reliability – Which drives last the longest in a NAS environment?
- SSD Cache Benefits – Speed up your Synology NAS with NVMe drives.