Storage Capacity Planner
Calculate realistic usable capacity by accounting for all overhead factors: RAID protection, hot spares, system reserves, and file system overhead.
Storage Configuration
Capacity Planning Guide
Storage capacity planning requires understanding the difference between raw capacity and usable capacity. When vendors advertise a 10TB drive, that's the raw capacity measured in decimal gigabytes (1GB = 1,000,000,000 bytes). However, operating systems typically report capacity in binary gigabytes (1GiB = 1,073,741,824 bytes), immediately showing ~7% less space. Check out our IOPS and throughput calculator.
Beyond the decimal vs binary difference, several overhead factors reduce usable capacity. RAID protection consumes capacity for parity or mirroring. System reserves hold space for metadata, snapshots, and array operations. File system formatting creates additional overhead for directories, journals, and allocation tables. Learn more: convert TB to TiB and storage units.
For accurate capacity planning, always calculate usable capacity using realistic overhead percentages. Enterprise arrays typically reserve 5-15% for system operations, while file systems consume 1-5% depending on block size and feature set. Planning with these factors ensures you don't over-commit storage resources. See also: StorageMath calculators.
Typical Overhead Values
- System Reserve (5-15%): Metadata, snapshots, thin provisioning overhead
- File System (1-5%): NTFS ~3%, ext4 ~1-2%, ZFS ~3-5%
- Hot Spares: 1 per 20 drives or 1-2 per RAID group recommended
- Growth Buffer: Consider 20-30% for future growth