Synology Disk Calculator
Estimate the usable storage capacity of your Synology NAS based on your drives and RAID configuration.
Total number of drive bays in your NAS.
Synology Hybrid RAID (SHR) is recommended for beginners.
Enter the capacity of a single disk. This calculator assumes all disks are the same size.
Choose the unit for the disk size entered.
What is a Synology Disk Calculator?
A synology disk calculator is an essential tool designed for current and future owners of a Synology Network Attached Storage (NAS) device. Its primary purpose is to demystify storage calculations by providing a clear estimate of the usable disk space you will have after configuring a RAID array. When you group multiple hard drives together in a NAS, not all of the raw capacity is available for storing your files. Depending on the RAID (Redundant Array of Independent Disks) type you choose, a portion of the storage is used for data protection, also known as redundancy. This calculator helps you make informed decisions by showing the trade-offs between raw capacity, usable space, and fault tolerance for different RAID levels like SHR, RAID 5, and RAID 6.
Anyone considering a multi-drive NAS, from home users setting up a media server to small businesses needing a central file repository, should use a synology disk calculator. It prevents surprises and helps in budgeting for the correct number and size of hard drives to meet specific storage goals. A common misunderstanding is that total storage is simply the sum of all disk capacities; this is only true for RAID 0, which offers zero data protection. This tool clarifies exactly how much space is dedicated to protecting your data from a drive failure.
The Formula Behind the Synology Disk Calculator
The calculation for usable space depends entirely on the selected RAID type. While Synology’s proprietary SHR (Synology Hybrid RAID) involves a more complex algorithm to optimize space with mixed-drive sizes, the principles for standard RAID levels (assuming identical disk sizes ‘S’ and number of disks ‘N’) are straightforward.
- SHR-1 / RAID 5: Provides a balance of efficiency and one-disk fault tolerance. The space of one disk is used for parity. Formula:
(N - 1) * S - SHR-2 / RAID 6: Offers enhanced protection with two-disk fault tolerance. The space of two disks is used for parity. Formula:
(N - 2) * S - RAID 1: Focuses on maximum redundancy by mirroring data. Half the total capacity is usable. Formula:
(N / 2) * S(typically used with 2 drives, resulting in 1*S). - RAID 10: A combination of speed (striping) and redundancy (mirroring). Like RAID 1, it uses half the capacity for protection. Formula:
(N / 2) * S - RAID 0: Prioritizes performance and capacity over safety, with no redundancy. All disk space is usable. Formula:
N * S
Variables Explained
| Variable | Meaning | Unit (Auto-Inferred) | Typical Range |
|---|---|---|---|
| N | Number of Disks | Unitless | 2 – 24+ |
| S | Capacity of a Single Disk | TB or GB | 1 TB – 22 TB |
| Usable Space | The final capacity available for data storage. | TB or GB | Varies based on inputs |
| Protection Space | Capacity reserved for data redundancy/fault tolerance. | TB or GB | Varies based on inputs |
Practical Examples
Example 1: Home User Setup
A home user wants to set up a media server for their family. They purchase a 4-bay Synology NAS and four 8 TB hard drives. To protect against a single drive failure without losing too much capacity, they choose SHR-1.
- Inputs: 4 disks, 8 TB disk size, SHR-1 RAID type.
- Units: Terabytes (TB).
- Results:
- Raw Capacity: 4 x 8 TB = 32 TB
- Usable Space: (4 – 1) x 8 TB = 24 TB
- Protection Space: 1 x 8 TB = 8 TB
Example 2: Small Business Setup
A small business needs reliable central storage for critical documents and backups. They opt for a 6-bay NAS with six 12 TB drives. Data integrity is paramount, so they choose RAID 6 for two-disk fault tolerance.
- Inputs: 6 disks, 12 TB disk size, RAID 6 type.
- Units: Terabytes (TB).
- Results:
- Raw Capacity: 6 x 12 TB = 72 TB
- Usable Space: (6 – 2) x 12 TB = 48 TB
- Protection Space: 2 x 12 TB = 24 TB
How to Use This Synology Disk Calculator
Using this calculator is simple and intuitive. Follow these steps to plan your storage configuration:
- Enter the Number of Disks: Input the total number of hard drives your Synology NAS will hold.
- Select the RAID Type: Choose a RAID configuration from the dropdown. For most users, SHR-1 is a great starting point, offering flexibility and one-disk protection. For more critical data, consider SHR-2 or RAID 6.
- Enter the Disk Size: Type the capacity of a single hard drive. This calculator assumes all drives are of the same size for simplicity.
- Select the Unit: Choose whether the disk size you entered is in Gigabytes (GB) or Terabytes (TB).
- Interpret the Results: The calculator will instantly update, showing you the ‘Total Usable Space’ as the primary result. You can also see the ‘Protection Space’ (how much is used for redundancy), the ‘Total Raw Capacity’, and the overall ‘Storage Efficiency’. The bar chart provides a quick visual breakdown.
Key Factors That Affect Storage Calculation
Several factors influence the final usable capacity from your Synology NAS.
- RAID Level: This is the most significant factor. RAID 0 offers 100% efficiency but no safety, while RAID 1/10 cuts usable space by 50% for high redundancy. RAID 5 and 6 offer a compromise.
- Number of Disks: More disks generally mean better efficiency in RAID 5 and 6. For example, in a RAID 5 array, 3 disks yield 67% efficiency, while 8 disks yield 87.5% efficiency.
- Disk Size Inconsistency: While this calculator assumes uniform disk sizes, Synology Hybrid RAID (SHR) is specifically designed to optimize capacity when using drives of different sizes—a key advantage over standard RAID. You can explore this further with Synology’s official RAID Calculator.
- File System Overhead: The file system itself (like Btrfs or ext4) reserves a small percentage of space for metadata. This can account for a 1-4% reduction in the space you see in the calculator versus what’s reported in the DSM operating system.
- Manufacturer’s Capacity Definition (TB vs. TiB): Hard drive manufacturers market capacity in terabytes (TB, base-10), but operating systems measure it in tebibytes (TiB, base-2). A “16 TB” drive is actually about 14.55 TiB, which is what your NAS will display. This accounts for a ~9% difference.
- System Partition: Synology’s operating system, DiskStation Manager (DSM), creates a small system partition on every drive, which further reduces the space available for the storage pool.
Frequently Asked Questions (FAQ)
- 1. What is SHR and how is it different from RAID?
- SHR (Synology Hybrid RAID) is Synology’s automated RAID system. Its main advantage is optimizing storage capacity when using disks of different sizes and simplifying expansion. SHR-1 is comparable to RAID 5 (1-disk protection), and SHR-2 is comparable to RAID 6 (2-disk protection).
- 2. Which RAID type is best for me?
- For most home users, SHR-1 is ideal due to its flexibility and balance of safety and capacity. For businesses or users with critical data, SHR-2 or RAID 6 provides superior protection. RAID 10 is best for performance-critical tasks like virtual machine hosting. Use this synology disk calculator to compare the space implications.
- 3. Can I mix hard drive sizes in a standard RAID?
- In standard RAID (like RAID 5/6), if you mix drive sizes, the array will treat all drives as if they are the size of the smallest drive in the set. This leads to wasted space. SHR is designed to overcome this limitation.
- 4. Why is the usable space shown in my NAS less than what the calculator shows?
- This is due to the difference between TB (decimal) and TiB (binary) measurements, as well as overhead from the operating system and file system. This calculator provides a close estimate, but the final figure in DSM will be slightly lower.
- 5. How many drive failures can each RAID type tolerate?
- RAID 0 and JBOD tolerate zero failures. RAID 1, RAID 5, and SHR-1 tolerate one failure. RAID 6, RAID 10 (with conditions), and SHR-2 tolerate two failures.
- 6. What happens if a disk fails in a redundant array?
- The array enters a ‘degraded’ state. Your data is still accessible, but performance will be reduced and you have no fault tolerance until you replace the failed drive and the array rebuilds.
- 7. Does RAID count as a backup?
- Absolutely not. RAID protects against hardware failure (a disk dying). It does NOT protect against file deletion, ransomware, corruption, or physical disaster (theft, fire). Always follow the 3-2-1 backup rule. A good place to start is our Data Backup Strategy Guide.
- 8. Can I change my RAID type later?
- Yes, Synology DSM allows you to change certain RAID types without data loss, such as migrating from SHR-1 to SHR-2 by adding another drive. However, not all migration paths are possible.
Related Tools and Internal Resources
Explore these resources to further optimize your storage and data management strategy.
- RAID 5 vs RAID 6 Performance: A deep dive into the performance and protection trade-offs between these two popular RAID types.
- What is a NAS?: A beginner’s guide to Network Attached Storage and how it can benefit you.
- SSD Cache Calculator: Determine the optimal SSD cache size for your Synology NAS to boost performance.
- Choosing the Right Synology NAS: A guide to help you select the perfect NAS model based on your needs.
- Plex Server Build Guide: Learn how to set up the ultimate media server on your Synology NAS.
- Data Backup Strategy Guide: Understand the best practices for creating a robust and reliable backup plan.