What this RAID throughput calculator estimates
This tool estimates theoretical sequential RAID throughput based on your chosen RAID level, drive count, and single-drive performance. It gives you fast planning numbers for storage designs such as NAS, backup targets, media servers, virtual machine datastores, and lab clusters.
The output includes:
- Estimated sequential read throughput (MB/s and GB/s)
- Estimated sequential write throughput (MB/s and GB/s)
- Mixed throughput based on your read/write percentage
- Raw and usable capacity in TB
- Capacity efficiency percentage
How to use the calculator
1) Select a RAID level
Pick the RAID layout you are considering: RAID 0, 1, 5, 6, or 10. Each one has different performance and capacity behavior because of striping, mirroring, and parity.
2) Enter drive count and per-drive speed
Use realistic values from your drive specs or benchmark data. If your drives are rated for 250 MB/s read and 220 MB/s write, enter those directly.
3) Add overhead and workload ratio
Overhead reflects file system, controller, protocol, and software stack losses. A common planning range is 8% to 20%. Then set read percentage to model your workload (for example, 70% reads and 30% writes).
Throughput formulas used in this model
The calculator uses a straightforward planning model:
- Read Throughput = Per-drive read × RAID read factor × (1 − overhead)
- Write Throughput = Per-drive write × RAID write factor × (1 − overhead)
- Mixed Throughput = (Read throughput × read %) + (Write throughput × write %)
RAID factors used
- Single Disk: read factor 1, write factor 1, capacity factor 1
- RAID 0: read factor N, write factor N, capacity factor N
- RAID 1 (2-disk model): read factor 2, write factor 1, capacity factor 1
- RAID 5: read factor N, write factor N−1, capacity factor N−1
- RAID 6: read factor N, write factor N−2, capacity factor N−2
- RAID 10: read factor N, write factor N/2, capacity factor N/2
Interpreting your results
Sequential numbers are not random I/O numbers
This calculator is designed for sequential throughput planning. Random IOPS behavior (small-block reads/writes) can be very different, especially on parity RAID where small writes may trigger read-modify-write penalties.
Network limits can dominate storage speed
Even if your array estimates 1,500 MB/s read throughput, a 1GbE link tops out around 110–120 MB/s in practice. For high-throughput arrays, verify network fabric (10GbE, 25GbE, Fibre Channel, etc.) before expecting full performance.
CPU, controller, and software stack matter
Software RAID can scale very well, but parity calculations, encryption, checksums, compression, and snapshots all consume resources. Treat results as a planning baseline, then validate with real benchmarks.
Example planning scenario
Suppose you configure 8 drives, each at 240 MB/s read and 210 MB/s write, using RAID 6 with 10% overhead and a workload that is 60% reads.
- Read estimate: 240 × 8 × 0.90 = 1,728 MB/s
- Write estimate: 210 × (8−2) × 0.90 = 1,134 MB/s
- Mixed estimate: 1,728 × 0.60 + 1,134 × 0.40 = 1,490.4 MB/s
This quickly tells you whether the array is likely to satisfy stream ingest, backup windows, or restore SLAs.
Design tips for better RAID performance
- Use matched drives where possible for predictable striping behavior.
- Avoid filling arrays to 95%+ utilization; performance can degrade significantly.
- Align file system block size and RAID stripe/chunk settings to workload patterns.
- For write-heavy workloads, compare RAID 10 against parity RAID for latency consistency.
- Benchmark with your actual application I/O profile, not just synthetic defaults.
Bottom line
A RAID throughput calculator is a fast way to estimate storage performance before you buy hardware or migrate data. Use it to compare architectures, then confirm with end-to-end tests in your own environment. Good planning up front prevents expensive under-sizing and reduces performance surprises later.