Synology Disk Calculator

Plan Your Storage Capacity and Performance

Storage Configuration

Storage Calculation Results

Total Usable Capacity: — TB
(Approximate, before DSM overhead)

Calculation Logic:

The usable capacity is determined by the RAID type, the number of disks, and the size of each disk. Different RAID levels consume a certain amount of capacity for redundancy (parity or mirroring). SHR is more flexible. Speed estimates are based on input values, though actual performance varies greatly with workload, drive type, and system configuration.

Usable Capacity Formula (Simplified):

For most RAID types (0, 1, 5, 6, 10): (Total Disks - Disks for Redundancy) * Disk Size

RAID 0: Total Disks * Disk Size

RAID 1: (Total Disks / 2) * Disk Size

RAID 5: (Total Disks - 1) * Disk Size

RAID 6: (Total Disks - 2) * Disk Size

RAID 10: (Total Disks / 2) * Disk Size

SHR: Varies based on disk configuration, aims to maximize usable space while allowing for different disk sizes (simplified here assuming equal sizes).

JBOD: Sum of all Disk Sizes (no redundancy).

Synology Storage Configuration Summary

Metric	Value	Unit
Total Disks	—	Drives
Selected RAID Type	—	Configuration
Individual Disk Size	—	TB
Total Raw Capacity	—	TB
Redundancy Disks/Overhead	—	Drives / TB
Max Tolerated Failures	—	Drives
Usable Capacity	—	TB
Estimated Max Read Speed	—	MB/s
Estimated Max Write Speed	—	MB/s

What is a Synology Disk Calculator?

A Synology Disk Calculator is an essential tool designed to help users estimate the storage capacity, performance, and redundancy levels of a Synology Network Attached Storage (NAS) device based on the drives installed and the chosen RAID configuration. Synology NAS devices offer a wide array of storage options, including various RAID types and their proprietary Synology Hybrid RAID (SHR). Understanding how these configurations impact your available storage space and data protection is crucial before purchasing hardware or setting up your NAS.

This calculator simplifies the complex calculations involved in determining usable storage. Whether you’re setting up a home media server, a business data backup solution, or a surveillance system, knowing your exact storage potential and redundancy safeguards is paramount for effective planning and avoiding future bottlenecks or data loss.

Who Should Use It?

• New Synology NAS Buyers: To determine the optimal number and size of drives for their budget and needs.
• Existing Synology Users: Planning to expand their storage or reconfigure their existing RAID setup.
• IT Administrators: Managing business data storage and ensuring data redundancy requirements are met.
• Home Users: Building a personal cloud, backing up photos/videos, or running media servers.

Common Misconceptions

• “More disks always mean more usable space”: This is only true for RAID 0 and JBOD. Most RAID levels (1, 5, 6, 10) sacrifice raw capacity for redundancy, meaning adding more disks might not linearly increase usable space, especially if it doesn’t align with the RAID’s redundancy scheme.
• “RAID protects against everything”: RAID protects against *drive failure*, not against accidental deletion, malware, fire, theft, or natural disasters. It is not a backup.
• “SHR is always the best choice”: SHR is excellent for flexibility, especially with mixed drive sizes, but traditional RAID levels can sometimes offer slightly better performance or predictability in specific scenarios.
• “Disk size is the only performance factor”: While disk size is critical for capacity, actual NAS performance is heavily influenced by the RAID type, network speed, CPU, RAM, and the specific workload (e.g., small file transfers vs. large file streaming).

Synology Disk Calculator Formula and Mathematical Explanation

The Synology Disk Calculator primarily focuses on calculating two key aspects: usable storage capacity and estimated performance. The underlying formulas vary depending on the selected RAID type.

Usable Capacity Calculation

This involves understanding how much storage is dedicated to redundancy (parity or mirroring) versus how much is available for data.

Variables:

Variable	Meaning	Unit	Typical Range
N	Total number of physical disks in the storage pool.	Drives	1+
S	Usable capacity of a single disk (after formatting).	TB	0.1 – 20+
F	Maximum number of disk failures tolerated.	Drives	0 to N-1
RAID_Type	The selected RAID configuration (e.g., RAID 0, RAID 5, SHR).	N/A	0, 1, 5, 6, 10, SHR, JBOD

Formulas by RAID Type:

• RAID 0 (Striping): No redundancy. Data is striped across all disks.
• Formula: Usable Capacity = N * S
• Redundancy: 0 Drives
• Max Failures: 0
• RAID 1 (Mirroring): Data is mirrored across pairs of disks. Minimum 2 disks.
• Formula: Usable Capacity = (N / 2) * S (assuming N is even)
• Redundancy: N / 2 Drives (capacity equivalent)
• Max Failures: 1 (if N=2), or 1 per pair
• RAID 5 (N-1 Parity): One disk’s worth of capacity is used for parity information distributed across all disks. Minimum 3 disks.
• Formula: Usable Capacity = (N - 1) * S
• Redundancy: 1 Drive (capacity equivalent)
• Max Failures: 1
• RAID 6 (N-2 Parity): Two disks’ worth of capacity is used for double parity. Minimum 4 disks.
• Formula: Usable Capacity = (N - 2) * S
• Redundancy: 2 Drives (capacity equivalent)
• Max Failures: 2
• RAID 10 (1+0): Combines mirroring and striping. Pairs of disks are mirrored, and then these pairs are striped. Minimum 4 disks.
• Formula: Usable Capacity = (N / 2) * S
• Redundancy: N / 2 Drives (capacity equivalent)
• Max Failures: 1 per mirrored pair (can be more if failures are in different pairs)
• SHR (Synology Hybrid RAID): Synology’s flexible RAID system. It allows for better usable space with mixed drive sizes and provides redundancy similar to RAID 1 or RAID 5/6 depending on the number of drives. For simplicity in this calculator, assuming equal drive sizes, SHR often behaves like RAID 5 for 3+ drives and RAID 1 for 2 drives, with scalability. The calculator uses a simplified model.
• Formula (Simplified, equal drives): Similar to RAID 5/6 depending on failure tolerance.
• Redundancy: Scales based on configuration.
• Max Failures: Configurable (typically 1 or 2).
• JBOD (Just a Bunch Of Disks): Disks are chained together linearly. No redundancy.
• Formula: Usable Capacity = N * S
• Redundancy: None
• Max Failures: 0 (failure of any single disk loses all data on that disk)

Note on SHR:

SHR’s calculation is complex due to its ability to mix drive sizes. The calculator provides an estimate. For exact figures with mixed drive sizes, refer to Synology’s official documentation.

Performance Calculation

Estimated speeds are based on the input values for read and write speeds. RAID configuration significantly impacts performance:

• RAID 0: Generally offers the highest read/write performance due to striping.
• RAID 1/10: Write performance is typically limited by the slowest drive in a mirrored pair, while read performance can be higher due to reads from multiple disks.
• RAID 5/6: Write performance can be slower than RAID 0 due to the parity calculation overhead. Read performance is usually good.
• JBOD: Performance is generally limited by the slowest single drive in the array.

Formula (Performance Estimate): The calculator uses the provided Estimated Read Speed and Estimated Write Speed directly, applying general RAID performance characteristics conceptually in the chart and discussion, rather than a strict mathematical formula for speed.

Practical Examples (Real-World Use Cases)

Here are a couple of scenarios illustrating how the Synology Disk Calculator can be used:

Example 1: Home Media Server Setup

User Need: A home user wants to consolidate their movie collection, photos, and music library onto a Synology NAS. They need good capacity and reasonable protection against drive failure.

• Proposed Configuration: 4 x 10TB drives.
• RAID Choice: SHR with 1 disk failure tolerance (common for flexibility and ease of management).

Calculator Inputs:

• RAID Type: SHR
• Number of Disks: 4
• Disk Size (TB): 10
• Max Disk Failures Tolerated: 1
• Estimated Read Speed (MB/s): 450
• Estimated Write Speed (MB/s): 250

Calculator Outputs (Approximate):

• Total Usable Capacity: ~27 TB
• Total Raw Capacity: 40 TB
• RAID Overhead/Parity: ~13 TB (equivalent of ~1.3 disks for SHR redundancy)
• Max Number of Drive Failures: 1
• Estimated Max Read Speed: 450 MB/s
• Estimated Max Write Speed: 250 MB/s

Interpretation: With 4 x 10TB drives in SHR allowing for one failure, the user gets approximately 27TB of usable space. This is sufficient for a large media library. The system can withstand the failure of one drive without data loss. Speeds are adequate for streaming media.

Example 2: Small Business Backup Solution

User Need: A small business needs a reliable NAS for backing up critical company data. High data integrity and redundancy are crucial.

• Proposed Configuration: 5 x 16TB drives.
• RAID Choice: RAID 6 for double disk failure protection.

Calculator Inputs:

• RAID Type: RAID 6
• Number of Disks: 5
• Disk Size (TB): 16
• Max Disk Failures Tolerated: 2
• Estimated Read Speed (MB/s): 600
• Estimated Write Speed (MB/s): 400

Calculator Outputs (Approximate):

• Total Usable Capacity: 48 TB
• Total Raw Capacity: 80 TB
• RAID Overhead/Parity: 32 TB (equivalent of 2 disks for RAID 6 parity)
• Max Number of Drive Failures: 2
• Estimated Max Read Speed: 600 MB/s
• Estimated Max Write Speed: 400 MB/s

Interpretation: Using RAID 6 with 5 x 16TB drives provides a substantial 48TB of usable storage. Crucially, the system can tolerate the simultaneous failure of any two drives, offering a high level of data protection vital for business continuity. The estimated speeds are good for handling frequent backups.

How to Use This Synology Disk Calculator

Using the Synology Disk Calculator is straightforward. Follow these steps to get an accurate estimate for your storage needs:

1. Select RAID Type: Choose the RAID configuration that best suits your needs for performance, capacity, and data protection. Common choices include SHR (Synology Hybrid RAID) for flexibility, RAID 5 for a balance of capacity and single-disk redundancy, or RAID 6 for double-disk redundancy.
2. Enter Number of Disks: Input the total count of physical hard drives you plan to install in your Synology NAS.
3. Enter Disk Size (TB): Specify the usable capacity of each individual disk in Terabytes (TB). Note: This should ideally be the advertised capacity minus a small percentage for formatting and file system overhead, though using the advertised capacity provides a good estimate.
4. Set Max Disk Failures Tolerated: Input the maximum number of drive failures your configuration should withstand. For SHR, this is usually 1 or 2. For traditional RAID, it’s 1 for RAID 5 and 2 for RAID 6. For RAID 1 or RAID 10, it’s effectively 1 per mirrored pair.
5. Estimate Speeds: Input your best guess for the sequential read and write speeds (in MB/s) your NAS setup will achieve. Consider your drive type (HDD vs. SSD), interface (SATA vs. NVMe), network speed (1GbE, 2.5GbE, 10GbE), and the NAS model’s capabilities. These are estimates; actual speeds vary.
6. Click “Calculate Storage”: Press the button to see the results.

How to Read Results

• Total Usable Capacity: This is the most important figure – the amount of space available for your data after accounting for the RAID configuration’s overhead.
• Total Raw Capacity: The sum of the capacities of all installed disks.
• Effective Capacity per Disk: How much capacity each disk effectively contributes to the usable pool, considering the RAID level.
• RAID Overhead/Parity: The amount of capacity consumed by the RAID configuration for redundancy.
• Max Number of Drive Failures: Confirms the level of data protection offered against drive failure.
• Estimated Max Read/Write Speed: Provides an idea of potential data transfer rates.

Decision-Making Guidance

Use the results to:

• Ensure you have enough storage for your current and future needs.
• Verify that your chosen RAID level provides adequate data protection.
• Compare different configurations (e.g., adding another drive, changing RAID type) to find the best balance of capacity, redundancy, and cost.
• Manage expectations regarding performance.

Key Factors That Affect Synology Disk Calculator Results

While the calculator provides estimates based on your inputs, several real-world factors can influence the actual results:

1. RAID Type Choice: This is the primary determinant of usable capacity and redundancy. RAID 0 maximizes capacity but offers no protection, while RAID 6 offers high protection but sacrifices more capacity. SHR offers flexibility, especially with mixed drive sizes.
2. Number of Disks: More disks generally mean more raw capacity. However, for redundant arrays (RAID 1, 5, 6, 10), the usable capacity scales differently than raw capacity. Adding disks to a RAID 5 array increases usable space by one full disk size per added disk.
3. Individual Disk Size: Larger disks directly increase both raw and potentially usable capacity. The calculator assumes all disks are the same size for simplicity, but SHR can handle mixed sizes, albeit with potential “wasted” space if smaller disks are added to a larger pool.
4. Drive Failure Tolerance: The number of disks you choose to tolerate failing directly impacts the capacity overhead. Tolerating 2 failures (like RAID 6 or SHR2) requires more capacity than tolerating only 1 failure.
5. Synology DSM Overhead: The DiskStation Manager (DSM) operating system itself consumes a small amount of storage space for its files and applications. This is usually a few gigabytes and is not factored into the calculator’s TB estimates.
6. File System Overhead: Modern file systems like Btrfs and ext4 have their own overhead for metadata, journaling, snapshots (on Btrfs), etc. This can reduce usable capacity slightly below the theoretical maximum.
7. Performance Variations:
   • Workload: Heavy multitasking, numerous small file transfers, or intensive database operations will perform differently than simple large file streaming.
   • Drive Type: SSDs offer significantly higher IOPS and sequential speeds than HDDs.
   • Network Infrastructure: A 1GbE network will bottleneck a NAS capable of 10GbE speeds.
   • NAS Model: CPU, RAM, and internal architecture of the Synology unit play a vital role in processing power and data throughput.
   • RAID Write Penalty: RAID 5 and RAID 6 have a write performance penalty due to parity calculations.
8. RAID Expansion Complexity: Expanding SHR or traditional RAID arrays can sometimes be complex or require specific steps. The calculator focuses on the static configuration state.

Frequently Asked Questions (FAQ)

Q1: What is the difference between SHR and traditional RAID?

SHR (Synology Hybrid RAID) is Synology’s automated RAID management system. It allows for greater flexibility, particularly when mixing drives of different sizes, and aims to maximize usable storage. Traditional RAID levels (0, 1, 5, 6, 10) follow strict rules for striping and parity/mirroring, offering predictable performance and capacity but less flexibility with drive sizes.

Q2: Can I mix drive sizes in a Synology NAS?

Yes, especially with SHR. If using traditional RAID types, all drives should ideally be the same size to avoid wasting capacity. For example, in a RAID 5 array with five 8TB drives and one 4TB drive, the array will function as if all drives were 4TB, wasting the unused space on the larger drives.

Q3: Does RAID protect against data deletion or ransomware?

No. RAID protects against physical hard drive failures only. It does not protect against accidental file deletion, hardware corruption, malware, or ransomware attacks. For comprehensive data protection, regular backups to a separate location (e.g., another NAS, cloud storage, external drive) are essential.

Q4: What is the best RAID type for performance?

Generally, RAID 0 offers the highest sequential read/write performance because data is striped across all drives without any overhead for redundancy. However, it provides zero data protection. RAID 10 also offers good performance, especially for mixed workloads.

Q5: What is the best RAID type for capacity?

RAID 0 and JBOD offer the maximum theoretical capacity as they don’t use space for redundancy. However, they are not recommended for any data that cannot be easily replaced due to the lack of protection. For protected storage, RAID 5 or SHR (with 1 drive failure tolerance) often provide a good balance.

Q6: How much usable space will I *really* get?

The calculator provides an estimate. Actual usable space can be slightly less due to Synology DSM operating system overhead, file system overhead (like Btrfs snapshots), and potential formatting differences. The calculated value is usually very close to reality.

Q7: Can I change my RAID type later?

Changing RAID types typically requires migrating data. For example, you might need to back up your data, create a new storage pool with the desired RAID type, and then restore the data. Synology DSM offers options like expanding existing storage pools or migrating from SHR to traditional RAID, but a full data migration is often the safest and most comprehensive approach.

Q8: What does “Max Disk Failures Tolerated” mean for SHR?

For SHR, this setting determines the redundancy level. Setting it to 1 provides redundancy equivalent to RAID 5 (tolerating one drive failure). Setting it to 2 (if supported by the NAS model and drive count) provides redundancy similar to RAID 6 (tolerating two drive failures). The calculator uses this input to inform the SHR capacity calculation.