RAID Rebuild Time Calculator

Work out raid rebuild time instantly with clear inputs, formula shown and shareable results.

About RAID Rebuild Time Calculator

Parity RAID rebuild must read every surviving disk in full to reconstruct the failed one, so read volume scales with array width while write volume is one disk. At 120 MB/s a 16 TB disk takes about 37 hours to write, and the whole array is degraded throughout — which is why RAID 5 on large modern disks is widely considered unsafe.

Formula

Rebuild time

parity RAID reads (disks - parity) x capacity and writes one capacity; time = max(read, write) bytes / rebuild rate

Worked example

With the default values below, RAID Rebuild Time Calculator returns Rebuild time of 222.2. Change any input above and every figure here is recalculated in your browser.

Inputs used

Disk capacityminimum 0.001 TB: 16 TB
Rebuild throughputminimum 0.1 MB/s: 120 MB/s
RAID levelone of RAID 1 mirror, RAID 5, RAID 6, RAID 10: RAID 6
Disks in the arrayaccepts 2–64: 8

Results

Rebuild time: 222.2 h
Rebuild time in seconds: 800,000 s
Data read during the rebuild: 87.31 TiB
Exposure during rebuild: RAID 6 survives a second failure during rebuild

Step by step

1Values used
2Rebuild time
3Rebuild time= 222.2 h
4Rebuild time in seconds= 800,000 s
5Data read during the rebuild= 96,000,000,000,000
6Exposure during rebuild= RAID 6 survives a second failure during rebuild

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why is RAID 5 discouraged on large disks?

Rebuild takes over a day, during which a second failure or an unrecoverable read error destroys the array. With multi-terabyte disks the probability of hitting one is no longer negligible.

Can rebuild be made faster?

Only by accepting more impact on production I/O, since rebuild throughput is throttled to preserve it. Faster rebuild is one of the main advantages of RAID 10 and of declustered parity.