Synology Disk Calculator

Accurately plan your Synology NAS storage with our advanced Synology Disk Calculator. Determine usable capacity based on your disk configuration and chosen RAID type (RAID 0, 1, 5, 6, 10, SHR-1, SHR-2) to optimize your data storage and redundancy needs.

Calculate Your Synology NAS Storage

Table 1: RAID Type Capacity Comparison (for 4 x 8TB Disks)

RAID Type	Minimum Disks	Usable Capacity (TB)	Redundancy	Best For
RAID 0	2	32	None	Maximum speed, no data protection
RAID 1	2	8	1 disk	High redundancy for small systems
RAID 5	3	24	1 disk	Good balance of capacity, performance, redundancy
RAID 6	4	16	2 disks	Higher redundancy, critical data
RAID 10	4 (even)	16	Half of disks	High performance and redundancy
SHR-1	1	24	1 disk	Flexible, optimized for mixed disk sizes
SHR-2	2	16	2 disks	Highest flexibility and redundancy for mixed disk sizes

What is a Synology Disk Calculator?

A Synology Disk Calculator is an essential online tool designed to help users estimate the usable storage capacity of their Synology Network Attached Storage (NAS) device. It takes into account critical factors such as the number of hard drives, their individual capacities, and the chosen RAID (Redundant Array of Independent Disks) configuration. This calculator provides a clear picture of how much space will be available for data storage after accounting for redundancy and system overhead.

Who Should Use a Synology Disk Calculator?

• Prospective Synology NAS Owners: To plan their initial purchase and ensure they buy enough disks for their needs.
• Existing Synology NAS Users: To evaluate expansion options, understand current capacity, or plan for future upgrades.
• IT Professionals: For designing storage solutions for clients or internal use, ensuring optimal capacity and data protection.
• Anyone Planning Data Storage: To understand the trade-offs between raw disk space and usable capacity based on redundancy requirements.

Common Misconceptions

Many users mistakenly believe that the usable capacity of a NAS is simply the sum of all disk capacities. This is a common misconception. RAID configurations, especially those designed for data redundancy (like RAID 1, 5, 6, 10, SHR-1, SHR-2), reserve a portion of the total raw disk space for parity information or mirroring. This overhead ensures data protection in case of disk failure, but it reduces the actual space available for your files. The Synology Disk Calculator clarifies this by showing the difference between raw and usable capacity.

Synology Disk Calculator Formula and Mathematical Explanation

The core of the Synology Disk Calculator lies in understanding how different RAID types allocate storage for redundancy. While the raw capacity is always the sum of all individual disk sizes, the usable capacity varies significantly.

Step-by-Step Derivation

Let’s define the variables:

• N = Number of Disks
• S = Individual Disk Size (in TB)
• Raw Capacity = N * S

The usable capacity (U) is then calculated based on the RAID type:

1. RAID 0 (Striping):

   U = N * S

   Explanation: All disks are combined into one large volume. There is no redundancy, so all raw capacity is usable. Requires at least 2 disks.

2. RAID 1 (Mirroring):

   U = S

   Explanation: Data is mirrored across disks. Only the capacity of one disk is usable, regardless of how many disks are in the array (as long as N >= 2). Requires at least 2 disks.

3. RAID 5 (Striping with Parity):

   U = (N - 1) * S

   Explanation: One disk’s worth of space is reserved for parity information, allowing for the failure of one disk without data loss. Requires at least 3 disks.

4. RAID 6 (Striping with Double Parity):

   U = (N - 2) * S

   Explanation: Two disks’ worth of space are reserved for parity, allowing for the failure of up to two disks without data loss. Requires at least 4 disks.

5. RAID 10 (Striping and Mirroring):

   U = (N / 2) * S

   Explanation: Disks are mirrored in pairs, and then these mirrored pairs are striped. Half of the total raw capacity is usable. Requires an even number of disks, at least 4.

6. Synology Hybrid RAID (SHR-1):

   For same-sized disks: U = (N - 1) * S

   Explanation: SHR-1 behaves like RAID 5 for same-sized disks, reserving one disk for parity. Its main advantage is optimizing capacity with mixed-sized disks, which is a more complex calculation not directly covered by this simplified calculator but explained in the article.

7. Synology Hybrid RAID (SHR-2):

   For same-sized disks: U = (N - 2) * S

   Explanation: SHR-2 behaves like RAID 6 for same-sized disks, reserving two disks for parity. It offers higher redundancy and flexibility with mixed-sized disks.

The Parity Overhead is simply Raw Capacity - Usable Capacity.

The Percentage Usable is (Usable Capacity / Raw Capacity) * 100.

Variables Table

Table 2: Key Variables for Synology Disk Calculation

Variable	Meaning	Unit	Typical Range
Number of Disks (N)	Total physical hard drives in the NAS	Count	1 to 16 (depending on NAS model)
Disk Size (S)	Capacity of a single hard drive	Terabytes (TB)	1 TB to 24 TB+
RAID Type	Redundancy configuration (e.g., RAID 5, SHR-1)	N/A	RAID 0, 1, 5, 6, 10, SHR-1, SHR-2
Raw Capacity	Total sum of all disk capacities	Terabytes (TB)	Varies widely
Usable Capacity	Actual storage space available for data	Terabytes (TB)	Varies widely
Parity Overhead	Space reserved for redundancy	Terabytes (TB)	0 to (N-1)*S

Practical Examples (Real-World Use Cases)

Understanding the Synology Disk Calculator with real-world scenarios helps in making informed decisions for your NAS setup.

Example 1: Home User with Data Redundancy Needs

A home user wants to store family photos, videos, and documents. They prioritize data protection over maximum capacity and plan to use a 4-bay Synology NAS.

• Inputs:
  • Number of Disks: 4
  • Disk Size: 8 TB each
  • RAID Type: Synology Hybrid RAID (SHR-1)
• Calculation:
  • Raw Capacity: 4 disks * 8 TB/disk = 32 TB
  • SHR-1 (like RAID 5 for same-sized disks) reserves 1 disk for parity.
  • Usable Capacity: (4 – 1) * 8 TB = 3 * 8 TB = 24 TB
  • Parity Overhead: 32 TB – 24 TB = 8 TB
  • Percentage Usable: (24 / 32) * 100 = 75%
• Interpretation: With 32 TB of raw storage, the user gets 24 TB of usable space. This configuration allows for one disk failure without data loss, providing a good balance of capacity and protection for personal data.

Example 2: Small Business Requiring High Redundancy

A small business needs a reliable storage solution for critical business documents and backups. They have an 8-bay Synology NAS and require protection against multiple disk failures.

• Inputs:
  • Number of Disks: 8
  • Disk Size: 12 TB each
  • RAID Type: RAID 6
• Calculation:
  • Raw Capacity: 8 disks * 12 TB/disk = 96 TB
  • RAID 6 reserves 2 disks for parity.
  • Usable Capacity: (8 – 2) * 12 TB = 6 * 12 TB = 72 TB
  • Parity Overhead: 96 TB – 72 TB = 24 TB
  • Percentage Usable: (72 / 96) * 100 = 75%
• Interpretation: The business has 96 TB of raw storage, yielding 72 TB of usable space. RAID 6 provides protection against two simultaneous disk failures, which is crucial for business continuity and data integrity. The 24 TB overhead is a necessary trade-off for this enhanced redundancy.

How to Use This Synology Disk Calculator

Our Synology Disk Calculator is designed for ease of use, providing quick and accurate storage estimates. Follow these simple steps:

1. Enter Number of Disks: In the “Number of Disks” field, input the total count of hard drives you plan to install or currently have in your Synology NAS. Ensure this is a valid number (e.g., 1 to 16).
2. Select Disk Size: From the “Disk Size (TB)” dropdown, choose the capacity of each individual hard drive. It’s assumed all disks are of the same size for the primary calculation, which simplifies understanding.
3. Choose RAID Type: Select your desired RAID configuration from the “RAID Type” dropdown. Options include standard RAID levels (RAID 0, 1, 5, 6, 10) and Synology’s proprietary Hybrid RAID (SHR-1, SHR-2).
4. View Results: As you adjust the inputs, the calculator will automatically update the “Usable Storage Capacity” (highlighted), “Raw Storage Capacity,” “Parity Overhead,” and “Percentage Usable” in real-time.
5. Read Formula Explanation: A brief explanation of how the calculation was performed for your chosen RAID type will be displayed below the results.
6. Analyze the Chart: The dynamic chart visually compares your raw and usable capacity, offering a clear perspective on storage allocation.
7. Copy Results: Use the “Copy Results” button to quickly save the calculated values and key assumptions for your records or sharing.
8. Reset: If you wish to start over, click the “Reset” button to restore the default input values.

How to Read Results

• Usable Storage Capacity: This is the most important number, representing the actual space you have for your data.
• Raw Storage Capacity: The total sum of all disk capacities before any RAID overhead.
• Parity Overhead: The amount of space dedicated to redundancy. A higher number here means better data protection but less usable space.
• Percentage Usable: Indicates the efficiency of your storage configuration.

Decision-Making Guidance

When using the Synology Disk Calculator, consider your priorities:

• Maximum Capacity: Choose RAID 0, but be aware of the complete lack of data protection.
• Data Redundancy: Opt for RAID 1, 5, 6, 10, SHR-1, or SHR-2. The more redundancy (e.g., RAID 6 or SHR-2), the less usable space but higher fault tolerance.
• Flexibility with Mixed Disks: SHR-1 and SHR-2 are generally recommended for Synology users, especially if you anticipate adding disks of different sizes in the future, as they optimize usable capacity better than traditional RAID levels in such scenarios.

Key Factors That Affect Synology Disk Calculator Results

Several critical factors influence the outcome of a Synology Disk Calculator and, more broadly, your NAS storage strategy. Understanding these helps in making optimal decisions.

1. Number of Disks: This is a primary driver. More disks generally mean more raw capacity and, for most RAID types, more usable capacity. However, it also increases the potential points of failure.
2. Individual Disk Size: Larger individual disk sizes directly translate to greater raw and usable capacity. It’s often more cost-effective to buy fewer, larger disks than many smaller ones, especially considering the fixed overhead of some RAID types.
3. RAID Type Selection: This is perhaps the most impactful factor. Different RAID levels offer varying trade-offs between capacity, performance, and data redundancy. RAID 0 maximizes capacity but offers no protection, while RAID 6 or SHR-2 prioritize redundancy at the cost of usable space.
4. Data Redundancy Needs: How critical is your data? If data loss is unacceptable, you’ll need a RAID type with redundancy (RAID 1, 5, 6, 10, SHR-1, SHR-2), which will reduce usable capacity. For less critical data, you might opt for RAID 0.
5. Future Expansion Plans: If you anticipate adding more disks later, Synology Hybrid RAID (SHR) is often the best choice. It allows for flexible expansion with different-sized disks, optimizing usable space in ways traditional RAID levels cannot. This is a key advantage of using a Synology Disk Calculator that considers SHR.
6. Performance Requirements: While not directly calculated by capacity, RAID types also affect performance. RAID 0 offers the fastest read/write speeds, while RAID 10 provides a good balance of speed and redundancy. RAID 5 and 6 offer decent performance but can be slower during rebuilds.
7. Cost Considerations: Larger disks and more disks increase the initial investment. The “cost per usable TB” can vary significantly between RAID types. For example, RAID 1 has a high cost per usable TB due to mirroring, while RAID 5 offers a better balance.
8. NAS Model Limitations: The physical number of drive bays in your Synology NAS model dictates the maximum number of disks you can use, directly impacting the Synology Disk Calculator’s inputs.

Frequently Asked Questions (FAQ)

Q: What is the difference between raw and usable capacity?

A: Raw capacity is the total sum of all disk capacities installed in your Synology NAS. Usable capacity is the actual storage space available for your files after the RAID configuration has reserved space for data redundancy (parity or mirroring).

Q: Why does the Synology Disk Calculator show less usable space than the sum of my disks?

A: This is because you’ve likely chosen a RAID type that provides data redundancy (e.g., RAID 1, 5, 6, 10, SHR-1, SHR-2). These configurations dedicate a portion of the raw disk space to protect your data against disk failures, reducing the usable capacity.

Q: What is Synology Hybrid RAID (SHR) and how does it differ from traditional RAID?

A: SHR is Synology’s proprietary RAID management system. It’s designed to optimize storage capacity when using disks of different sizes, unlike traditional RAID levels which are most efficient with identical disk sizes. SHR-1 provides single-disk redundancy, and SHR-2 provides dual-disk redundancy.

Q: Can I mix different sized disks in my Synology NAS?

A: Yes, you can, especially with Synology Hybrid RAID (SHR). SHR is specifically designed to make the most of mixed-sized disks, whereas traditional RAID levels (like RAID 5 or 6) would limit all disks to the size of the smallest disk in the array, wasting capacity.

Q: What is the minimum number of disks required for each RAID type?

A: RAID 0 and RAID 1 require at least 2 disks. RAID 5 and SHR-1 require at least 3 disks (SHR-1 can start with 1 disk, but redundancy requires 2+). RAID 6, RAID 10, and SHR-2 require at least 4 disks (SHR-2 can start with 2 disks, but redundancy requires 3+).

Q: Does the Synology Disk Calculator account for file system overhead?

A: No, this Synology Disk Calculator primarily focuses on the raw vs. usable capacity based on RAID configuration. File system overhead (e.g., Btrfs or ext4) and other system partitions will consume a small additional amount of space, typically a few gigabytes, which is not factored into these calculations.

Q: How does the calculator handle disk sizes in TB vs. TiB?

A: Hard drive manufacturers market disk sizes in terabytes (TB), where 1 TB = 1,000,000,000,000 bytes. Operating systems and NAS devices often report capacity in tebibytes (TiB), where 1 TiB = 1,099,511,627,776 bytes. This calculator uses the manufacturer’s TB values for consistency, but be aware of the slight discrepancy you might see reported by your NAS.

Q: Why is the “Copy Results” button useful?

A: The “Copy Results” button allows you to quickly save or share the calculated usable capacity, raw capacity, parity overhead, and the chosen configuration. This is helpful for documentation, comparing different setups, or discussing your storage plans with others.

Related Tools and Internal Resources

To further assist you in your storage planning and Synology NAS journey, explore these related tools and articles:

• RAID Capacity Planning Guide: Learn more about optimizing your storage for various RAID levels.
• NAS Storage Solutions for Home and Business: Discover different NAS setups and their benefits.
• Understanding Data Redundancy Strategies: Deep dive into how RAID protects your data and best practices.
• Synology SHR Explained: Hybrid RAID Benefits: A comprehensive guide to Synology’s flexible storage technology.
• Disk Space Optimization Techniques: Tips and tricks to get the most out of your available storage.
• RAID Level Comparison Chart: Compare different RAID types side-by-side for performance, capacity, and redundancy.