Advanced RAID Capacity & Performance Calculator

RAID (Redundant Array of Independent Disks) is a foundational storage virtualization technology that combines multiple physical disk drives into one or more logical units. The goals are typically to improve data redundancy, increase performance, or achieve a balance of both. Understanding the different RAID levels is crucial for protecting your data and optimizing your storage for specific workloads.

Common RAID Levels Explained

• RAID 0 (Striping): Data is split evenly across two or more disks. This provides a significant performance boost for read and write operations since multiple disks are working in parallel.
  • Use Case: Video editing scratch disks, image processing, or any task requiring fast, temporary storage where data loss is not a concern.
  • Warning: RAID 0 has no fault tolerance. If a single drive fails, all data across the entire array is lost.
• RAID 1 (Mirroring): Data is written identically to two or more disks. This provides excellent data redundancy.
  • Use Case: Operating system drives, small databases, or any application where data availability is critical and capacity is not the primary concern.
  • Benefit: The array can withstand the failure of all but one drive. Read performance may be slightly improved, but write performance is comparable to a single drive.
• RAID 5 (Striping with Distributed Parity): Data and parity information are striped across three or more drives. Parity data is a calculated value that allows data to be reconstructed if one drive fails.
  • Use Case: General-purpose file servers and application servers where a good balance of storage efficiency and data protection is needed.
  • Consideration: Suffers from a "write penalty" because each write operation requires an additional parity calculation. Rebuild times can be long for large arrays, increasing the risk of a second drive failure.
• RAID 6 (Striping with Double Parity): An extension of RAID 5 that uses two independent parity blocks. This allows the array to tolerate the failure of up to two drives simultaneously.
  • Use Case: Archival storage, large-scale file servers, and any critical data where extended rebuild times are a concern. Highly recommended over RAID 5 for arrays with large-capacity drives.
• RAID 10 (Stripe of Mirrors): A "nested" RAID level that combines the mirroring of RAID 1 with the striping of RAID 0. It requires a minimum of four drives.
  • Use Case: High-performance databases, virtual machines, and applications with a high volume of random read/write operations.
  • Benefit: Offers the high performance of striping with the redundancy of mirroring, providing a robust and fast solution at the cost of 50% storage efficiency.
• RAID 50/60 (Stripe of Parity Arrays): Nested RAID levels that stripe across multiple RAID 5 (RAID 50) or RAID 6 (RAID 60) sets. These offer improved performance and faster rebuild times compared to a single large RAID 5/6 array.

Key RAID Concepts

Parity Data

A calculated value derived from a block of data. In RAID 5 or 6, if a drive fails, the system can use the parity information on the remaining drives to mathematically reconstruct the missing data. This is the foundation of RAID's efficiency over simple mirroring.

Unrecoverable Read Error (URE)

Modern hard drives have a URE rate, typically 1 bit in every 10^14 or 10^15 bits read. During a RAID 5 rebuild, the system must read every bit from the remaining drives. With today's large multi-terabyte drives, the chance of encountering a URE during a rebuild is statistically significant, which would cause the rebuild to fail. This is the primary argument for using RAID 6 on large arrays.

Hardware vs. Software RAID

Hardware RAID uses a dedicated controller card to manage the array, offloading work from the CPU. For an in-depth comparison, ServeTheHome has an excellent guide. Software RAID is managed by the operating system (e.g., Windows Storage Spaces, ZFS, mdadm in Linux). It's cheaper but uses system resources and may be less robust in a power failure.

Frequently Asked Questions (FAQ)

Choosing a RAID level involves trade-offs between cost, speed, and data safety. This calculator helps you navigate those choices.

• What is the best RAID for a home NAS?

  For most home users, proprietary systems like Synology Hybrid RAID (SHR) or a standard RAID 5 provide a great balance of capacity and protection. For a 2-drive system, RAID 1 is the standard choice.

• Should I use RAID 5 with large drives?

  It is increasingly discouraged. As explained in the URE section above, the probability of a read error during the long rebuild process of a multi-terabyte drive is high. A second drive failure or URE during this vulnerable period will result in total data loss. For arrays over 8-10TB or using drives larger than 4TB, RAID 6 is strongly recommended.

• What is ZFS and how is it different?

  ZFS is an advanced file system with integrated volume and RAID-like management (e.g., RAID-Z). It offers powerful features like data integrity protection against bit rot, snapshots, and copy-on-write. You can learn more at the OpenZFS project website.

For a comprehensive overview of all standard RAID levels, we recommend the RAID article on Wikipedia.