Synology Calculator for RAID & Storage
An expert tool to plan your Network Attached Storage (NAS) capacity.
Hard Drive Configuration
RAID Configuration
Not enough drives for this RAID level.
What is a Synology Calculator?
A Synology Calculator is a specialized tool designed to help users plan and visualize the storage capacity of their Synology Network Attached Storage (NAS) device. Unlike a generic math calculator, it specifically computes the usable disk space based on the number of drives, their individual sizes, and the selected RAID (Redundant Array of Independent Disks) level. This is crucial for anyone setting up a new NAS, as the advertised raw capacity of the drives is often very different from the actual space available for data after accounting for data redundancy (protection against drive failure).
This tool is essential for home users, IT professionals, and businesses who rely on Synology for data storage, backups, or multimedia streaming. By using a Synology Calculator, you can make informed decisions about which drives to purchase and what RAID configuration best suits your needs for performance, storage space, and data safety. A common misunderstanding is that RAID is a backup; it is not. RAID provides redundancy to protect against drive failure, but you still need a separate backup strategy.
Synology Calculator Formula and Explanation
The calculation for usable storage depends entirely on the chosen RAID level. Each level offers a different balance between performance, storage capacity, and fault tolerance.
The formula varies by RAID type. For example, RAID 5 uses the capacity of one drive for parity, so the formula is `(Number of Drives – 1) * Size of Smallest Drive`.
Variables Table
| Variable | Meaning | Unit (Auto-Inferred) | Typical Range |
|---|---|---|---|
| Drive Size | The individual capacity of a hard drive. | TB or GB | 1 – 22 TB |
| Number of Drives | The total count of drives in the array. | Count (unitless) | 2 – 16 |
| RAID Level | The chosen redundancy configuration (e.g., SHR, RAID 5). | Enum (text) | SHR, RAID 0/1/5/6 |
| Usable Capacity | The final storage space available for your data. | TB | Varies |
Practical Examples
Example 1: A Common Home NAS Setup
A user wants to set up a 4-bay Synology NAS for home media and backups. They choose four 8 TB drives and opt for Synology’s recommended SHR for a balance of flexibility and one-drive protection.
- Inputs: 4 x 8 TB drives
- RAID Level: SHR (equivalent to RAID 5 in this case)
- Calculation: (4 drives – 1 for protection) * 8 TB = 24 TB
- Result: The user gets approximately 24 TB of usable space and can withstand the failure of a single drive without data loss. For more on RAID types, see our guide on choosing the right data protection.
Example 2: Mixed-Size Drive Scenario
A user is upgrading their NAS and has two 4 TB drives and two new 10 TB drives. They want to maximize their storage using SHR.
- Inputs: 2 x 4 TB drives, 2 x 10 TB drives
- RAID Level: SHR
- Calculation: SHR intelligently creates logical volumes. It will create a RAID 5-like array using 4 TB from each of the four drives (giving (4-1)*4=12 TB). It then creates a RAID 1-like array with the remaining 6 TB on the two larger drives (giving 6 TB of usable space).
- Result: The user gets approximately 18 TB (12 TB + 6 TB) of usable space. A traditional RAID 5 would have treated all drives as 4 TB, yielding only 12 TB total. This highlights the power of the Synology Calculator in planning for mixed-drive environments.
How to Use This Synology Calculator
Follow these simple steps to determine your potential storage capacity:
- Enter Drive Sizes: In the “Hard Drive Configuration” section, enter the capacity of each drive you plan to use. If you are not using all 8 slots, leave the unused inputs as 0.
- Select Unit: Choose whether the drive sizes you entered are in Terabytes (TB) or Gigabytes (GB).
- Choose RAID Level: Select your desired RAID configuration from the dropdown menu. For most users, SHR-1 is the recommended starting point.
- Review Results: The calculator will instantly update. The “Total Usable Capacity” is your primary result. You can also see the total raw capacity, the amount of space dedicated to protection, and the overall storage efficiency.
- Analyze Chart: The visual bar chart helps you quickly understand the relationship between usable space and protected space.
Key Factors That Affect Synology Calculator Results
- RAID Level: This is the single biggest factor. RAID 0 offers the most space but no protection, while RAID 1 offers the most protection but only 50% space efficiency with two drives. RAID 5/6 and SHR offer a balance.
- Number of Drives: More drives generally mean more potential capacity. However, some RAID levels like RAID 6 require a minimum of four drives to even function.
- Drive Size Homogeneity: With traditional RAID (5, 6), if you use drives of different sizes, the array will treat all drives as if they are the size of the smallest drive in the set. SHR is designed to overcome this limitation.
- Fault Tolerance: The number of drives you want to be able to fail without losing data directly impacts usable space. SHR-1 and RAID 5 have 1-drive tolerance. SHR-2 and RAID 6 have 2-drive tolerance, which uses more space for protection.
- File System Overhead: The calculator provides a very close estimate, but the actual formatted capacity will be slightly less due to space reserved for the file system’s metadata (e.g., Btrfs or ext4).
- System Partition: A small amount of space on each drive is reserved for the Synology DSM operating system itself, which is not available for user data. Explore our advanced storage solutions to learn more.
Frequently Asked Questions (FAQ)
What is the difference between SHR and RAID 5?
If all your drives are the same size, SHR-1 is functionally identical to RAID 5. The main advantage of SHR is its ability to optimize storage capacity when you use drives of different sizes, a scenario where RAID 5 is very inefficient.
Why is the usable capacity less than the total size of my drives?
This is due to data redundancy. RAID levels like SHR, RAID 1, 5, and 6 use a portion of the total capacity to store parity data or mirror data. This data is what allows the system to rebuild your information if a drive fails.
How many drives can fail in SHR-1 vs SHR-2?
SHR-1 (like RAID 5) provides one-drive fault tolerance. SHR-2 (like RAID 6) provides two-drive fault tolerance, offering a higher level of data protection at the cost of less usable space.
Can I mix drive sizes in this Synology Calculator?
Yes. This calculator is designed to handle mixed drive sizes, and it will accurately show you the benefits of choosing SHR over traditional RAID in such a setup.
Should I use TB or GB in the calculator?
You can use either. Just be sure to select the correct unit from the “Drive Size Unit” dropdown so the calculations are accurate. The results will be displayed in TB for easier understanding of large capacities.
Is RAID a backup?
No, this is a critical point. RAID protects against hardware failure of a disk. It does not protect against file deletion, corruption, malware/ransomware, or physical disaster (fire, theft). You still need a comprehensive 3-2-1 backup strategy.
What happens if I don’t have enough drives for a selected RAID level?
The calculator will display an error message and show 0 for the results. For example, RAID 6 requires a minimum of four drives.
Why choose SHR-2 over SHR-1?
SHR-2 is recommended for larger arrays (e.g., 5+ drives). During the time it takes to rebuild an array after a single drive failure (which can be days), the remaining drives are under heavy stress. SHR-2 ensures that even if a second drive fails during this critical rebuild process, your data remains safe.
Related Tools and Internal Resources
Explore more of our tools and guides to optimize your data management strategy.
- NAS Selector Tool: Find the perfect Synology NAS model for your needs.
- Data Backup Best Practices: Learn how to create a robust backup plan.
- Performance Tuning your NAS: Tips and tricks to get the most speed out of your setup.