STORAGE / LOCAL CALCULATION
RAID / ZFS calculator
Compare hardware or software RAID, RAIDZ and dRAID. Build a pool with several data vdevs and calculate nominal capacity with exact whole-byte arithmetic.
Disk layout
Enter a layout and calculate capacity.
Capacity estimate
- Installed raw capacity
- Hot spares, excluded from the array
- Distributed spare capacity
- Parity / mirrored-copy capacity
- Nominal capacity after redundancy
- Exact nominal-model bytes
- Selected reserve
- Capacity after selected reserve
Exact arithmetic applies to the nominal model. Actual filesystem space differs due to metadata, sector alignment, RAIDZ/dRAID padding, snapshots and compression. Hot spares do not increase failure tolerance. TiB display rounds to two decimals.
Choose a layout for your workload
Hardware and software implementations share capacity geometry but differ in supported levels, cache protection and rebuild behavior. Historical RAID 2/3 and controller-specific RAID 1E/00 are planning models; check your hardware manual. RAID 01 and RAID 10 have different failure-placement rules.
Multiple ZFS vdevs provide separate I/O groups and expansion options. Each vdev pays its own redundancy cost. Losing any top-level data vdev can lose the whole pool. Mixed layouts can have uneven performance and resilience; a larger capacity number is not a performance benchmark.
dRAID can rebuild into distributed spare space using sequential I/O across surviving disks. Its fixed-width stripes add padding for small blocks and may reduce compression benefits. A checksum scrub follows sequential resilvering. Spare capacity does not add a parity level. RAID is not a backup.
OpenZFS vdev and dRAID definitions