Unraid Write Path Estimator: Normal vs Turbo Write

This Unraid write path estimator explains what happens to a file when it's written to your Unraid array based on cache pool presence, drive type, and turbo write setting. Clarifies cache bypass, mover behaviour, and when turbo write is safe to use.

Turbo Write (formerly called Reconstruct Write) sounds like a free speed upgrade, but it's not always faster, and it comes with trade-offs. Whether it helps you depends on how many drives you have, what you're writing, and whether your drives are already spinning.

This tool estimates real-world write speeds for both modes under your setup, and tells you plainly when Turbo Write is worth enabling.

Important: You generally won't see better than a single drive's sequential write speed writing to the array: Normal Write is often far below it. Turbo Write can get much closer in the right setup, but results depend on drive count, the slowest disk, and your controller. This tool shows speeds as absolute ranges for both modes.

Your Array Setup

Write source mainly affects write pattern (sequential vs random, sustained vs bursty). Turbo Write helps most with sustained sequential writes regardless of source.

Normal Write
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Drives active
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Est. power
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Best for
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Turbo Write
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Drives active
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Est. power
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Best for
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Controller may be a bottleneck
Mover and Turbo Write Turbo Write can speed up Mover writes when moving large sequential files and when most drives are already spinning. If the mover job would spin up the whole array for every run, the extra power and noise may outweigh the benefit. If your array is already active when the mover runs, Turbo Write may still help. Consider the CA Auto Turbo Write Mode plugin for automatic switching based on drive spin state.
Slowest disk limits Turbo Write throughput
SMR drives and Turbo Write SMR drives perform poorly under the sustained write patterns Turbo Write generates. If you have SMR drives in your array, Turbo Write may cause write stalls rather than speed improvements. CMR drives are strongly recommended for Unraid data and parity disks.

Single-drive speed: You generally won't see better than a single drive's sequential write speed writing to the array: Normal Write is often far below it, and Turbo Write can get much closer in the right setup. The comparison here is Normal Write vs Turbo Write under your specific configuration.

Normal Write (Read-Modify-Write) is constrained by platter rotation: after reading old data and parity and calculating new parity, the drive must wait for the write position to rotate back around. This rotation penalty significantly reduces throughput, commonly observed at 50-100 MB/s for sustained array writes on 7200 RPM HDDs.

Turbo Write (Reconstruct Write) eliminates the rotation wait by writing data immediately and reconstructing parity in parallel from all other drives. Typically 2-3x faster than Normal Write for sustained large sequential writes, and can get close to single-drive speed in large arrays with fast CMR drives and a good HBA, though results depend on drive count, the slowest disk, and controller limits.

Auto Turbo Mode: The CA Auto Turbo Write Mode plugin (Community Applications) automatically switches between modes based on how many drives are currently spinning. Unraid also has a built-in Auto write mode option, the CA plugin extends this by switching dynamically based on real-time spin state. This is the recommended approach for most users.

Further reading: Unraid array write modes, official docs (Read/Modify/Write vs Turbo Write/Reconstruct Write).

Speed ranges reflect typical real-world throughput reported by the Unraid community for each drive count and class. File size modifiers account for the overhead of small-file operations under both write paths. Controller caps reflect real bandwidth constraints on shared-bus onboard SATA implementations.

Power draw is estimated using typical active read/write wattage per drive class (7200 RPM HDD: ~9 W, 5400 RPM: ~7 W). AU electricity rate used: $0.30/kWh.

Last reviewed: 20 March 2026

Frequently Asked Questions

Turbo Write writes new data immediately, then reads all other data drives simultaneously to reconstruct parity. It is typically 2-3x faster than Normal Write for sustained large sequential writes. Normal Write is often far below single-drive speed; Turbo Write can get much closer in larger arrays with the right setup. The cache pool bypasses parity overhead entirely for initial writes.
Writing to the array always involves parity. Normal Write reads old data and parity before writing (rotation penalty). Turbo Write reads all drives to reconstruct parity after writing (reconstruction overhead). The cache pool bypasses this for initial writes, if raw write speed matters, writing to cache first is the right approach. The array write speed is the speed after the Mover has moved data from cache to the parity-protected array.
The CA Auto Turbo Write Mode plugin (Community Applications) automatically switches between Normal and Turbo Write based on how many drives are currently spinning. When most drives are already active, it switches to Turbo Write to maximise throughput. When drives are spun down, it stays on Normal Write to avoid the spin-up cost. Unraid also has a built-in Auto write mode option (Settings → Disk Settings), the CA plugin extends this by switching based on real-time spin state. This is the recommended approach for most users.
No. Parity integrity is maintained in both modes: Turbo Write just uses a different calculation path to the same parity result. Your array is no less protected with Turbo Write enabled. During a drive failure, parity will correctly reconstruct missing data regardless of which write mode was used.
It depends on your usage pattern. If Turbo Write causes all drives to spin up for every small write, more spin cycles accumulate over time, and drive spin-up is one of the higher-wear events in a HDD's life. For users who write infrequently or have a mostly idle array, Normal Write is kinder to drives. For arrays in continuous heavy use where drives are always spinning, the difference is negligible.
Yes. Settings → Disk Settings. Changes take effect on the next write operation. No array stop is required. This makes it easy to test both modes and observe the difference in your own dashboard.
Possibly, but more likely culprits are drives spinning up from a stopped state (the first write after idle will be slow regardless of mode), the cache pool filling up (writes bypass the parity array until then), or a single slow drive acting as a bottleneck. Check per-drive activity in the Unraid dashboard during a sustained transfer to diagnose. Also confirm whether your writes are going to cache or directly to the array.
Rarely. Container and VM writes are typically random and bursty: Turbo Write's reconstruction overhead costs outweigh its benefits for these workloads. The recommendation is to store VM images and container appdata on a cache pool (SSD) rather than the parity-protected array. Array storage is best used for large media files and backups where sequential throughput matters.

AU Cache SSD Pricing: Enabling Turbo Write (early 2026)

Turbo Write (Reconstruct Write) reads all data drives simultaneously, which requires all drives to be spinning. For home NAS users who want Turbo Write performance without spin-up delays, pairing it with a cache pool is the recommended approach. Cache SSD prices from Mwave, PLE, Amazon AU.

DriveCapacityAU retail rangeBest for
Samsung 870 EVO500 GB$75-$95Small cache pool: SOHO or home with light writes
Samsung 870 EVO1 TB$120-$145Standard home cache, most 4-bay Unraid builds
WD Red SN700 NVMe1 TB$130-$160High-throughput writes, media ingest, VM workloads
WD Red SN700 NVMe2 TB$230-$270Large active dataset, production media library

Normal vs Turbo Write: AU Home NAS Decision Summary

For a typical AU home Unraid build with 4-6 data drives in an energy-saving spin-down config, Normal Write is usually the better default. Turbo Write shines when your workload keeps drives spinning anyway, use this estimator to check whether your scenario actually benefits.

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