How long does it take to rebuild a 12TB drive in a NAS?
As a theoretical floor, a 12TB drive read or written flat-out at 180–260 MB/s sustained takes roughly 13–19 hours. Real rebuilds run longer — parity computation, concurrent use and throttling add time, and an SMR drive can multiply it. Start promptly, keep load light and use CMR drives.
Last verified July 22, 2026 · 2 official sources checked Updated
This is a floor, not a promise: it assumes the drive reads or writes flat-out at the rate you set, with nothing else happening. Real rebuilds run longer — parity computation, using the NAS during the rebuild, and drive throttling all add time, and an SMR drive can multiply it. Sustained rates for current 3.5-inch NAS drives run roughly 180–280 MB/s (see each drive’s datasheet); 200 MB/s is a reasonable middle default.
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At 12 TB the numbers get long enough that the second-failure risk during the rebuild becomes the real story. Start with the floor, then the caveats.
The theoretical floor
Capacity ÷ sustained transfer rate is the fastest a rebuild could possibly finish. Current 3.5-inch NAS drives publish sustained rates around 180–260 MB/s. A 12 TB drive: 12,000,000 MB ÷ (180–260 MB/s) ≈ 13–19 hours as a floor. The estimator above defaults to 12 TB — change the rate to match your drive's datasheet.
Why real rebuilds run longer
- Parity computation for RAID 5/6/SHR is extra work.
- Concurrent use of the NAS slows the rebuild.
- Throttling trades speed for responsiveness.
- SMR drives can turn this into days.
Why it matters
A 12 TB single-parity rebuild can take the best part of a day with no fault tolerance the whole time — a second drive failing loses the pool. At this capacity, RAID 6 / SHR-2 is worth it: double parity survives a failure during the long rebuild. Use CMR drives and start promptly. The table lists in-stock 12 TB CMR drives by price per terabyte.
12 TB CMR drives, by CA$/TB
Live Amazon.ca prices in CAD, ranked by price per terabyte. The Recording column is verified against manufacturer documentation.
Related questions
Sources
Every technical claim on this page is checked against manufacturer and standards documentation. Dates are when each source was last reviewed.
- Seagate — IronWolf Pro datasheet (Max Sustained Transfer Rate OD, up to ~285 MB/s) — checked 2026-07-22
- Synology KB — Repair a Storage Pool — checked 2026-07-22