Synology Disk Calculator

RAID & Storage Calculator

Estimate your usable storage capacity and data redundancy based on your drive configuration and chosen RAID type. This tool helps you plan your storage before purchasing a Synology NAS.

Analysis & Comparison

RAID Type	Min. Disks	Usable Capacity	Fault Tolerance

Table: Comparison of usable capacity across different RAID types for your configuration.

What is a Synology Disk Calculator?

A synology disk calculator is an essential planning tool for anyone considering a Network Attached Storage (NAS) device. It allows you to simulate a storage setup to understand exactly how much usable space you will get from a given number of hard drives and a specific RAID configuration. RAID (Redundant Array of Independent Disks) is a technology that combines multiple physical disks into one or more logical units for data redundancy, performance improvement, or both. The choice of RAID type directly impacts usable capacity, and this tool demystifies that calculation.

This synology disk calculator is designed for prospective and current Synology owners, IT administrators, photographers, videographers, and home users who need to plan their storage needs accurately. One common misconception is that total storage is simply the sum of all drive capacities. However, for any RAID level that provides data protection (like SHR, RAID 5, or RAID 6), a portion of the total capacity is reserved for redundancy, which is why a synology disk calculator is so invaluable for accurate planning.

Synology Disk Calculator Formula and Mathematical Explanation

The calculation of usable storage space depends entirely on the selected RAID type. Each has a different approach to balancing performance, capacity, and redundancy. Our synology disk calculator automates these formulas for you.

Here’s a step-by-step breakdown of the most common RAID types:

• SHR (Synology Hybrid RAID): With 1-disk protection (SHR-1), the capacity of the largest drive is reserved for protection. Usable space is the sum of the remaining drives. For drives of the same size, it behaves like RAID 5. A synology disk calculator helps visualize this, especially with mixed drive sizes.
• RAID 0 (Striping): Combines all disks into a single volume for maximum performance and capacity. It has no redundancy. The formula is: Usable Capacity = (Number of Disks) x (Disk Capacity).
• RAID 1 (Mirroring): Writes identical data to two or more disks. It provides excellent redundancy but at the cost of capacity. The formula is: Usable Capacity = (Disk Capacity of Smallest Drive).
• RAID 5 (Striping with Parity): Stripes data and parity information across three or more disks. It can withstand the failure of one disk. The formula is: Usable Capacity = (Number of Disks – 1) x (Disk Capacity).
• RAID 6 (Striping with Dual Parity): Similar to RAID 5 but uses two parity blocks, allowing it to withstand the failure of two disks. The formula is: Usable Capacity = (Number of Disks – 2) x (Disk Capacity).
• RAID 10 (Mirroring and Striping): A ‘nested’ RAID level combining the speed of RAID 0 with the redundancy of RAID 1. It requires an even number of disks (min 4). The formula is: Usable Capacity = (Number of Disks / 2) x (Disk Capacity).

Variable	Meaning	Unit	Typical Range
Number of Disks	Total count of hard drives in the NAS	Integer	2 – 24
Disk Capacity	Storage size of a single hard drive	Terabytes (TB)	1 – 22
RAID Type	Selected data redundancy configuration	Enum	SHR, RAID 0/1/5/6/10
Usable Capacity	The final storage space available for data	Terabytes (TB)	Varies

Practical Examples (Real-World Use Cases)

Example 1: The Freelance Photographer

A photographer needs a robust backup solution with redundancy. They choose a 4-bay Synology NAS and purchase four 10 TB hard drives. Using our synology disk calculator, they select SHR (which behaves like RAID 5 in this case).

• Inputs: 4 Disks, 10 TB Capacity, SHR-1
• Outputs:
  • Raw Capacity: 40 TB
  • Usable Capacity: 30 TB
  • Protection Capacity: 10 TB
  • Fault Tolerance: 1 Drive

Interpretation: The photographer gets 30 TB of usable space, which is ample for their photo libraries. More importantly, they are protected against a single drive failure, safeguarding their critical client work. Check out our guide on NAS backup strategies to learn more.

Example 2: The Small Business Office

A small business needs a central file server with a high degree of data protection for 5-10 employees. They opt for a 5-bay NAS with five 16 TB drives and want 2-drive fault tolerance. They use the synology disk calculator to compare SHR-2 and RAID 6.

• Inputs: 5 Disks, 16 TB Capacity, RAID 6
• Outputs:
  • Raw Capacity: 80 TB
  • Usable Capacity: 48 TB
  • Protection Capacity: 32 TB
  • Fault Tolerance: 2 Drives

Interpretation: The business achieves 48 TB of usable storage while being able to withstand two simultaneous drive failures. This high level of redundancy is critical for business continuity. Our article on understanding RAID levels provides more context.

How to Use This Synology Disk Calculator

Using this synology disk calculator is a straightforward process designed to give you instant clarity on your potential storage setup.

1. Enter the Number of Disks: Input the total quantity of drives you plan to install in your Synology NAS.
2. Set the Disk Capacity: Provide the capacity of a single drive in Terabytes (TB). For simplicity, our calculator assumes all drives are of identical size.
3. Select the RAID Type: Choose your desired RAID configuration from the dropdown menu. If you’re new to RAID, Synology Hybrid RAID (SHR) is highly recommended for its flexibility.
4. Analyze the Results: The synology disk calculator will instantly update the “Total Usable Capacity” and other key metrics. The primary result shows the space you’ll have for your files.
5. Review the Comparison Table and Chart: The dynamic table and chart help you compare how different RAID levels affect your total available space and redundancy, making it easier to decide on the right balance for your needs. Explore our NAS selection guide for further reading.

Key Factors That Affect Synology Disk Calculator Results

The results from any synology disk calculator are influenced by several critical factors. Understanding them is key to making an informed decision.

• RAID Type: This is the most significant factor. RAID 0 offers the most space but no protection, while RAID 1 and 6 offer high protection but sacrifice more capacity. SHR provides a balanced, flexible approach.
• Number of Drives: More drives generally mean more capacity and, for some RAID types, better performance. However, it also increases the initial cost.
• Drive Capacity: Larger drives provide more raw space, but remember that in redundant arrays (RAID 1, 5, 6, 10), the capacity used for protection also increases.
• Synology Hybrid RAID (SHR) vs. Classic RAID: SHR is unique to Synology and offers significant advantages when using drives of different sizes, minimizing wasted space. A standard synology disk calculator often simplifies this, but the underlying benefit is crucial for future expansion.
• Fault Tolerance Needs: How much data loss can you afford? If none, you need at least 1-drive fault tolerance (SHR, RAID 1, 5). For mission-critical data, 2-drive fault tolerance (SHR-2, RAID 6, RAID 10) is recommended.
• File System Overhead: The Btrfs file system, used by modern Synology devices, reserves about 4% of space for metadata and snapshots. Our synology disk calculator provides the storage pool capacity; the final volume will be slightly less. Consider reading about Btrfs vs ext4 for more details.

Frequently Asked Questions (FAQ)

1. What is the best RAID for a home user?

For most home users, Synology Hybrid RAID (SHR) is the best choice. It provides 1-disk fault tolerance, is flexible for future expansion with different-sized drives, and is easy to manage. It offers a great balance of safety and capacity that you can model with this synology disk calculator.

2. Can I mix drive sizes in a Synology NAS?

Yes, especially if you use SHR. While traditional RAID types are inefficient with mixed-sized drives (they treat all drives as if they were the size of the smallest drive), SHR is designed to optimize capacity from a mixed-drive setup. Our advanced SHR calculator can model this.

3. How many drives can fail in RAID 5?

RAID 5 can withstand the failure of exactly one drive. If a second drive fails before the first one is replaced and the array is rebuilt, all data on the volume will be lost.

4. Is RAID 0 a good idea?

RAID 0 offers the best performance and 100% capacity utilization, but it has zero fault tolerance. If any single drive fails, all data across all drives is lost. It is only recommended for temporary storage of non-critical data, like video editing scratch disks.

5. What’s the difference between SHR and SHR-2?

SHR (or SHR-1) provides 1-drive fault tolerance, similar to RAID 5. SHR-2 provides 2-drive fault tolerance, similar to RAID 6. Use the synology disk calculator to see the capacity difference; SHR-2 sacrifices an additional drive’s worth of capacity for increased data safety.

6. Why is the usable capacity less than what the synology disk calculator shows?

There are two main reasons. First, drive manufacturers market capacity in decimal (1 TB = 1,000,000,000,000 bytes), while operating systems measure in binary (1 TiB = 1,099,511,627,776 bytes). This accounts for about a 9% difference. Second, the file system (e.g., Btrfs) reserves a small percentage of space for metadata.

7. How many drives do I need for RAID 6?

You need a minimum of four drives for a RAID 6 array. This is because two drives’ worth of capacity is dedicated to parity (data protection), leaving the rest for usable storage.

8. Can I change my RAID type later?

Synology’s DiskStation Manager (DSM) allows for changing certain RAID types without data loss. For example, you can migrate from SHR-1 to SHR-2 by adding a drive, or from RAID 1 to RAID 5. However, you cannot migrate to a RAID level with less protection (e.g., from RAID 5 to RAID 0). A synology disk calculator is your best friend for initial planning.