RAID Performance Calculator

Configuration preset:

Pick a NAS or VM-cluster baseline, then replace any value with your real design.

Workload profile:

Use only when the profile matches the dominant workload; Custom preserves manual values.

Drive media profile:

Select HDD, SSD, or NVMe for rough planning, or Custom for measured drive benchmarks.

RAID level:

Select the layout to model: RAID 0, 1, 5, 6, 10, 50, or 60.

Drives per group:

Use one parity set or mirror stripe width; RAID 6 needs at least 4 active drives.

drives

Group count:

Use 1 for a single group, or 2+ for RAID 50/60 sets and repeated vdev-style groups.

groups

Hot spares:

Enter dedicated global spares; they are removed from the widest groups first.

drives

Per-drive random IOPS:

Use measured single-drive random IOPS at the queue depth closest to your workload.

Read IOPS:

Example: 85000 for a mixed-use enterprise SSD.

Write IOPS:

Example: 42000 for sustained random writes on the same drive.

Per-drive sequential throughput:

Enter sustained per-drive read/write MB/s from datasheet or benchmark, not array totals.

Read MB/s:

Example: 540 for one SATA SSD read stream.

Write MB/s:

Example: 500 for one SATA SSD write stream.

Read share: {{ mixLabel }}

Enter 0-100; 70 means a 70% read / 30% write workload.

Block size:

Use KiB per operation, e.g. 4 for OLTP, 16 for VM, 256 for backup streams.

KiB

Drive size:

Enter the advertised drive size in decimal TB, e.g. 7.68 or 18.

Rebuild baseline:

Use measured rebuild/resilver bandwidth per drive; HDDs may be 120-260 MB/s.

MB/s

Target IOPS:

Set 0 to skip IOPS target checks; otherwise enter required safe blended IOPS.

IOPS

Target throughput:

Set 0 to skip throughput target checks; otherwise enter required safe MB/s.

MB/s

Comparison priority:

Balanced is neutral; Performance or Resilience biases the comparison matrix.

Read-cache boost: {{ advanced.read_cache_boost_pct }}%

Use 0-60%; keep 0 unless cache hit rate is known or tested.

Write-cache boost: {{ advanced.write_cache_boost_pct }}%

Use 0-80%; stay conservative for sustained writes beyond cache destage.

Parity efficiency:

Use 100% for nominal math; lower values reduce parity RAID write performance.

Queue-depth efficiency: {{ advanced.queue_depth_efficiency_pct }}%

Use 100% for benchmark-like queues; reduce for shallow or constrained workloads.

Stripe alignment penalty: {{ advanced.stripe_alignment_penalty_pct }}%

Use 0-40%; raise for small random writes, snapshots, or misaligned block paths.

Rebuild reserve: {{ advanced.rebuild_reserve_pct }}%

Use 0-80%; higher reserve lowers safe output but protects rebuild windows.

Degraded write drag: {{ advanced.degraded_write_penalty_pct }}%

Use 0-90%; raise when controllers throttle writes during degraded operation.

Full-stripe write share: {{ advanced.full_stripe_write_pct }}%

Use 0 for random writes, higher values for backup or large sequential ingest.

Controller cap (IOPS):

Set 0 to disable; otherwise enter the maximum array IOPS the controller can sustain.

IOPS

Controller cap (MB/s):

Set 0 to disable; otherwise enter the maximum safe MB/s for the path.

MB/s

Base read latency:

Set 0 for auto-estimate, or enter measured single-drive read latency in ms.

Base write latency:

Set 0 for auto-estimate, or enter measured single-drive write latency in ms.

Controller latency overhead:

Enter extra ms from HBA, cache, SAN, or network path; 0 keeps media-only latency.

Target safety margin:

Use 0-100%; 20 means targets must clear by 20% to be comfortably sized.

Snapshot precision:

Choose 0-4 decimals; IOPS still display as whole numbers.

Metric	Value	Copy
{{ row.label }}	{{ row.value }}

Scenario	Safe IOPS	Safe MB/s	Retention	Target fit	Copy
{{ row.scenario }}	{{ row.safeIopsDisplay }}	{{ row.safeMbsDisplay }}	{{ row.retentionDisplay }}	{{ row.targetFitDisplay }}

Constraint	Current effect	Severity	Recommendation	Copy
{{ row.constraint }}	{{ row.effect }}	{{ row.severity }}	{{ row.recommendation }}

RAID	Penalty	Safe IOPS	Safe MB/s	Usable TB	Efficiency	Fault tolerance	Rebuild ETA	Target fit	Copy
{{ row.levelLabel }} Recommended	{{ row.writePenaltyDisplay }}	{{ row.safeIopsDisplay }}	{{ row.safeMbsDisplay }}	{{ row.usableDisplay }}	{{ row.efficiencyDisplay }}	{{ row.faultLabel }}	{{ row.rebuildDisplay }}	{{ row.targetFitDisplay }}

Mix	Safe IOPS	Safe MB/s	Target delta	Status	Copy
{{ row.mixLabel }}	{{ row.safeIopsDisplay }}	{{ row.safeMbsDisplay }}	{{ row.targetGapDisplay }}	{{ row.statusText }}

Write locality	Penalty	Safe IOPS	Safe MB/s	Degraded retention	Target fit	Interpretation	Copy
{{ row.shareLabel }} Selected	{{ row.effectivePenaltyDisplay }}	{{ row.safeIopsDisplay }}	{{ row.safeMbsDisplay }}	{{ row.retentionDisplay }}	{{ row.targetFitDisplay }}	{{ row.interpretation }}

Field	Value	Copy
{{ row.label }}	{{ row.value }}

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RAID performance planning turns single-drive benchmark numbers into a storage budget that can survive real read/write mix, write locality, rebuild work, and controller limits. A disk or SSD can advertise strong random IOPS and sequential MB/s, but the RAID layout decides how each logical request fans out across the members. Striping spreads work, mirroring duplicates writes, and parity layouts spend extra I/O to keep reconstructable data.

The first useful distinction is workload shape. A mostly-read database cache, a mixed virtualization cluster, and a backup repository can use the same disks and RAID level yet produce very different safe budgets. Small random writes expose parity or mirror write penalty. Larger aligned writes may behave closer to full-stripe activity, especially for backup, ingest, or analytic workloads. Block size matters too because an IOPS budget converts into throughput only after the average KiB per operation is known.

Read/write mix: Shifts the budget between read scaling and write penalty exposure.
RAID geometry: Sets usable drives, parity or mirror overhead, minimum drive rules, and failure behavior.
Write locality: Separates small random writes from aligned full-stripe writes that reduce parity overhead.
Reserve and caps: Hold back performance for rebuild work or clamp the estimate to a known controller, HBA, fabric, or appliance ceiling.

Capacity and performance overlap, but they are not the same decision. RAID 6 can be attractive for capacity and dual-parity protection while still being weak for heavy random writes. RAID 10 often gives stronger mixed random performance with lower usable capacity. Hot spares improve recovery posture, yet they reduce the active disks that can serve work. A controller cap can make additional drives irrelevant if the host path is already the bottleneck.

A RAID estimate should be read as a planning budget, not a benchmark. It can narrow a design, expose an unrealistic target, and show which assumption is carrying the result. It cannot prove latency under production load, guarantee rebuild behavior, or replace backup and recovery design.

How to Use This Tool:

Start with a realistic storage shape, then tighten the assumptions until the summary and result tabs match the design you actually intend to deploy.

Pick a Configuration preset when it is close to your plan, or leave Custom and choose the RAID level, drives per group, group count, and hot spares manually. Watch for an Input conflict alert when the active drive count no longer satisfies the selected RAID level.
Choose the Drive media profile, then replace Read IOPS, Write IOPS, Read MB/s, Write MB/s, Drive size, and Rebuild baseline with measured numbers when you have them.
Set Workload profile, Read share, and Block size so the calculator models the dominant I/O pattern instead of an ideal benchmark. The read-share value should match the expected read/write split, such as 70R / 30W for many VM workloads.
Open Advanced when cache, parity efficiency, queue-depth efficiency, stripe alignment, full-stripe write share, rebuild reserve, degraded write drag, controller caps, or latency assumptions are known enough to model.
Enter Target IOPS, Target throughput, and Target safety margin when the design must clear a service goal. The summary badge will distinguish target met, margin short, and target not met states.
Review Performance Snapshot first, then compare Degraded Scenarios, Performance Constraints, RAID Level Comparison, Read-Write Mix Sweep, Write Locality Sweep, RAID Headroom Bars, and IOPS Budget Donut before treating one layout as preferred.

If Safe blended IOPS changes sharply when Read share or Full-stripe write share moves, treat that assumption as the first item to verify with traces or benchmark data.

Interpreting Results:

The headline IOPS number is the modeled safe blended IOPS for the selected RAID level after the read/write mix, penalty, efficiency, reserve, and caps are applied. The matching safe throughput is limited by the sequential path and by the block-size conversion from IOPS to MB/s, so it can be much lower than the sum of drive datasheet throughput.

RAID performance result interpretation
Output	What to check	Why it matters
Safe blended IOPS	Compare it with Target IOPS and the safety-margin delta.	Shows the planned random I/O budget after the major holdbacks.
Safe blended throughput	Check whether the Throughput limiter is media, block-size IOPS, or controller cap.	Prevents mistaking high sequential drive rates for usable workload throughput.
Worst single-group failure	Compare degraded IOPS and MB/s with the same targets.	Healthy-state success is not enough if rebuild mode misses the service goal.
Write-locality sweep	Look at the difference between 0% and 100% full-stripe writes.	Large swings mean the write-pattern assumption needs evidence from traces or tests.
Primary constraint	Read the recommendation before changing drives or RAID level.	It points to the limiter most likely to change the result.

Do not treat the Recommended badge as an automatic design choice. It is a weighted comparison of performance, resilience, degraded retention, and capacity efficiency under the selected priority mode. Validate the chosen layout against real controller behavior, queue depth, caching policy, filesystem alignment, rebuild policy, and backup requirements.

Technical Details:

RAID performance math starts with independent drive service rates and then changes them according to layout. Reads can often scale with active member count, while writes must respect the chosen protection scheme. RAID 0 has no redundancy and uses a write penalty of 1. Mirrored layouts duplicate writes. Parity layouts such as RAID 5 and RAID 6 update parity information, so small random writes spend more physical I/O per logical write.

Nested layouts add another layer of geometry. RAID 50 behaves like multiple RAID 5 groups striped together, and RAID 60 does the same with RAID 6 groups. Hot spares are withheld from active service, so they reduce the drives that contribute to capacity and performance. The calculator allocates spares across groups, checks minimum group rules, and treats odd active counts as invalid for mirror-based RAID levels that require even membership.

Formula Core:

The core estimate blends read and write service rates, applies reserve and caps, then converts IOPS to an MB/s ceiling with the selected block size.

\begin{array}{lcl} P_{eff} & = & P_{random} \times (1 - F) + P_{stripe} \times F \\ I_{read} & = & N \times I_{drive-read} \times C_{read} \\ I_{write} & = & \frac{N \times I_{drive-write}}{P_{eff}} \times E \times C_{write} \times A \\ I_{mixed} & = & Q \times (r \times I_{read} + (1 - r) \times I_{write}) \\ I_{safe} & = & \min (I_{controller-cap}, \sum I_{mixed} \times (1 - R)) \\ M_{safe} & = & \min (M_{seq-safe}, M_{controller-cap}, I_{safe} \times \frac{B_{KiB}}{1024}) \end{array}

Controller-cap terms act as no ceiling when their fields are set to 0. When a cap is entered, it becomes an upper bound after the RAID math, so additional drives cannot raise the modeled result past that limit.

Formula symbols for RAID performance estimate
Symbol	Meaning	Visible input or output
N	Active drives in a RAID group after hot spares are removed.	Drives per group, Group count, Hot spares
r	Read share as a decimal from 0 to 1.	Read share
F	Share of writes modeled as full-stripe writes.	Full-stripe write share
E, Q, A	Parity efficiency, queue-depth efficiency, and stripe-alignment factor.	Advanced settings
R	Rebuild reserve held back from the safe budget.	Rebuild reserve
B	Average operation size in KiB.	Block size

RAID write penalty and capacity behavior
RAID level	Random write penalty	Usable-drive rule	Failure model used
RAID 0	x1	All active drives	No failed-drive operation
RAID 1	x2	Half of active drives	One failure per mirror pair
RAID 5	x4	Active drives minus one per group	One failed data drive per group
RAID 6	x6	Active drives minus two per group	Two failed data drives per group
RAID 10	x2	Half of active drives	One failure per mirror pair
RAID 50	x4	RAID 5 usable drives across two or more groups	One failed drive per RAID 5 group
RAID 60	x6	RAID 6 usable drives across two or more groups	Two failed drives per RAID 6 group

Degraded operation is modeled by reducing the selected level's safe IOPS and MB/s with separate read and write retention factors, then applying the degraded write drag setting. The worst single-group failure becomes the degraded figure shown in the headline and failure table. Rebuild ETA uses drive size, rebuild MB/s, rebuild reserve, and the selected level's rebuild complexity factor, so a large HDD parity group can have a long degraded window even when its healthy throughput looks acceptable.

The calculator rounds display values according to Snapshot precision, with IOPS shown as whole numbers in most tables. Exact exported values should still be treated as model output, not measured storage behavior.

Accuracy Notes:

The calculation runs from the values entered in the browser. It does not benchmark disks, query a controller, test filesystem alignment, verify cache protection, or inspect a live array.

Use sustained drive numbers at a queue depth and block size close to the real workload.
Keep controller caps enabled when an HBA, appliance, SAN path, or network link is the known ceiling.
Do not rely on RAID 0 for protected storage; the modeled degraded result is array loss.
Use backups, snapshots, and recovery testing separately from RAID fault tolerance.

Worked Examples:

A virtualization plan with RAID 10, two groups of 10 SAS SSDs, no hot spares in the active model, 72R / 28W mix, 8 KiB blocks, 18% rebuild reserve, and a 20% safety margin produces about 1,502,912 Safe blended IOPS and 11,741.50 Safe blended throughput. Worst single-group failure remains about 85.9% of healthy IOPS, so the Target with safety margin met badge is plausible for a 650,000 IOPS and 5,200 MB/s target.

A balanced RAID 6 plan with two groups of eight SATA SSDs and one global spare leaves 7 and 8 active drives per group. With a 70R / 30W mix, 16 KiB blocks, 20% full-stripe writes, and a 20% rebuild reserve, the model shows about 686,245 Safe blended IOPS, 4,506.85 Safe blended throughput, and 84.48 TB usable capacity. The Write locality sweep is worth checking because the effective write penalty is still about x5.07.

A RAID 10 plan with five active drives in one group does not produce a performance estimate. The page reports an Input conflict because RAID 10 requires an even active drive count per group. Fix the topology before comparing Safe blended IOPS, RAID Headroom Bars, or the Recommended badge.

Advanced Tips:

Replace media-profile defaults with measured Read IOPS, Write IOPS, Read MB/s, and Write MB/s when you have data from the same queue depth and block size as the workload.
Use the Write Locality Sweep before trusting a parity RAID result. A large gap between random writes and full-stripe writes means the estimate depends heavily on batching, alignment, or controller cache behavior.
Keep Controller cap IOPS and Controller cap MB/s enabled when the HBA, fabric, appliance, or network path is the real ceiling; otherwise the model may reward extra drives that cannot be used.
Check Worst single-group failure against the same target as the healthy state. A layout that passes only before rebuild pressure is not a complete service plan.
Use Comparison priority deliberately. Performance-first, resilience-first, and balanced scoring weight the same RAID rows differently, so the recommended level should match the operational goal.

FAQ:

Why does RAID 10 often look better for mixed random writes?

RAID 10 uses a lower random write penalty than parity RAID, so a workload with meaningful writes can keep more Safe blended IOPS even when it gives up usable capacity.

Why can a higher full-stripe write share improve parity RAID?

Aligned full-stripe writes reduce the parity read-modify-write cost. The Write Locality Sweep shows how much the selected RAID level depends on that assumption.

Why is safe throughput lower than drive MB/s multiplied by drives?

Safe blended throughput is limited by sequential media math, controller caps, and the conversion from Safe blended IOPS through the selected Block size.

What should I do with an Input conflict?

Adjust Drives per group, Group count, or Hot spares until the selected RAID level's minimum and even-count rules are satisfied, then rerun the comparison.

Can this replace a storage benchmark?

No. Use it for planning and comparison, then verify the selected layout with representative workload tests, controller documentation, and rebuild drills.

Glossary:

Safe blended IOPS: Modeled random I/O budget after read/write mix, write penalty, efficiency, reserve, and caps.
Write penalty: Extra physical operations needed for one logical write under the selected RAID layout.
Full-stripe write: An aligned write pattern that can reduce parity overhead by writing complete stripes.
Rebuild reserve: Performance held back so degraded service and rebuild work are not ignored.
Degraded retention: The percentage of healthy-state IOPS or throughput expected to remain during a modeled failure.
Controller cap: A configured IOPS or MB/s ceiling for the host path, controller, fabric, or storage appliance.

References:

RAID level summary, IBM Power documentation, 12 May 2022.
Real World Workloads, SNIA.
Overview of Hardware or Operating System Striping, Oracle Database 21c documentation.
Supported Levels for Intel RAID Controllers, Intel, last reviewed 03 Sep 2024.
How to improve GlusterFS performance, Simplified Guide.
How to profile GlusterFS volume performance, Simplified Guide.

RAID Performance Calculator

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How to Use This Tool:

Interpreting Results:

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Worked Examples:

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FAQ:

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RAID Performance Calculator

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Introduction

How to Use This Tool:

Interpreting Results:

Technical Details:

Formula Core:

Accuracy Notes:

Worked Examples:

Advanced Tips:

FAQ:

Glossary:

References: