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RAID CAPACITY CALCULATOR

Calculate the true usable capacity of your NAS or server array. This tool automatically accounts for the decimal-to-binary conversion tax (so a 10 TB drive correctly registers as ~9.1 TB of actual OS space) and subtracts parity overhead for all major RAID levels instantly.

Drives

Understanding RAID Storage & The "Missing" Capacity

  • RAID: Redundant Array of Independent Disks
  • NAS: Network Attached Storage

When you buy a brand new "10 TB" hard drive, plug it in, and see only 9.1 TB available in Windows, you haven't been scammed. This discrepancy is due to how storage manufacturers versus operating systems calculate data.

  • Manufacturers use Base 10 (Decimal): To them, 1 Kilobyte = 1,000 bytes. So, 1 Terabyte (TB) is exactly 1,000,000,000,000 bytes.
  • Operating Systems use Base 2 (Binary): Computers count in binary, where 1 Kilobyte = 1,024 bytes. Therefore, 1 Tebibyte (TiB) is 1,099,511,627,776 bytes.

Our calculator automatically applies this conversion (TB * 0.909, or GB * 0.931) so you get the exact usable space you will see on your monitor, not the marketing numbers on the box.

A Quick Breakdown of Common RAID Levels

RAID 0 (Striping): Splits data evenly across two or more disks with zero parity. It offers the maximum possible speed and utilizes 100% of your disk space. Warning: If a single drive dies, you lose all data on all drives.

RAID 1 (Mirroring): An exact clone of your data on two drives. You only get the capacity of one drive, but if one drive fails, the other keeps running perfectly. Great for critical OS drives.

RAID 5 (Striping with Parity): The most popular NAS configuration. It requires at least 3 drives. Data and parity blocks are striped across all drives. You lose the equivalent capacity of exactly one drive, but any single drive can fail without data loss.

RAID 6 (Double Parity): Similar to RAID 5, but requires at least 4 drives and uses double the parity. You lose the capacity of two drives, but your array can survive two simultaneous drive failures. Highly recommended for arrays using 8TB+ drives.

RAID 10 (Stripe of Mirrors): Combines the speed of RAID 0 with the safety of RAID 1. Requires a minimum of 4 drives (and must be an even number). You lose exactly 50% of your raw capacity, but it provides incredible read/write performance and fast rebuild times.

Important Reminder

RAID is not a backup. RAID protects against hardware failure to keep your system online. It does not protect against ransomware, accidental file deletion, or theft. Always keep a separate, off-site backup of your critical data following the 3-2-1 backup strategy.

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