RAID Speed Calculator
Estimate usable capacity and theoretical read/write throughput for common RAID configurations.
What This RAID Speed Calculator Tells You
This tool provides a quick estimate of how a RAID array might perform before you buy hardware or reconfigure storage. It calculates three practical outputs:
- Estimated read throughput in MB/s
- Estimated write throughput in MB/s
- Usable capacity after RAID overhead (mirroring/parity)
The numbers are intentionally conservative. Real benchmarks can be higher or lower depending on controller quality, queue depth, stripe size, filesystem settings, CPU overhead, and network limits (if using NAS).
How RAID Levels Affect Speed
RAID 0 (Striping)
RAID 0 maximizes speed because data is split across all drives with no redundancy. Read and write throughput scale almost linearly with the number of disks. The tradeoff is risk: if any drive fails, the full array is lost.
RAID 1 (Mirroring)
RAID 1 duplicates data for redundancy. Reads can improve because the system can pull from multiple mirrored copies, but writes are typically constrained because every block must be written to each mirror copy.
RAID 5 (Single Parity)
RAID 5 balances usable capacity and fault tolerance. Sequential reads are often strong, but writes are reduced by parity calculations and additional write operations. For random-write heavy workloads, the penalty can be significant.
RAID 6 (Dual Parity)
RAID 6 can survive two drive failures, making it attractive for larger arrays. In exchange, parity overhead is heavier than RAID 5, especially on write-intensive workloads.
RAID 10 (Striped Mirrors)
RAID 10 combines striping and mirroring. It generally offers very good read and write behavior with strong fault tolerance, but usable capacity is typically half of raw disk capacity.
Example: Planning a 4-Drive Home Lab Array
Suppose you have four 4 TB drives with around 220 MB/s read and 210 MB/s write per drive. If you compare RAID 5 and RAID 10:
- RAID 5 gives more usable capacity (about 12 TB from 16 TB raw), but writes can drop in parity-heavy patterns.
- RAID 10 gives less usable capacity (about 8 TB) but usually better write consistency and faster rebuild behavior.
The “best” option depends on your goal: capacity efficiency, speed consistency, or resilience during failures.
Why Real-World Results Differ from Calculators
- Drive type: SSD, HDD, and SMR drives behave very differently.
- Controller quality: Hardware RAID cards and software RAID stacks vary widely.
- Workload shape: Sequential transfer tests are easier than random mixed read/write workloads.
- Filesystem tuning: ZFS, Btrfs, XFS, ext4, and NTFS all have different behavior.
- Network bottlenecks: A 1 GbE link caps practical throughput near 110–120 MB/s no matter how fast your RAID is.
Practical Tips for Better RAID Performance
- Use drives with similar size and speed to avoid uneven bottlenecks.
- Choose stripe/chunk sizes based on workload (larger for media, tuned for virtualization).
- Keep firmware and controller drivers updated.
- Watch rebuild times; larger arrays take longer and can expose risk windows.
- Remember: RAID improves availability, not backup safety. Keep independent backups.
Bottom Line
A RAID speed calculator is best used as a planning tool, not a final benchmark. Use these estimates to compare architectures, then validate with real tests in your environment. If your workload is write-heavy and latency-sensitive, parity RAID often looks better on paper than in production. For balanced reliability and performance, RAID 10 is commonly chosen despite lower usable capacity.