How to use this calculator
- Enter or choose drive capacity.
- Enter or choose size unit.
- Enter or choose sustained rebuild rate.
- Enter or choose share of the drive to rebuild.
- The rebuild time updates as you type. Use Copy result or Share to keep it.
Method
Time (s) = Drive capacity (bytes) × Share ÷ (Rate × 10⁶ bytes/s)
- Drive capacity
- decimal: 1 TB = 10¹² bytes
- Rate
- megabytes (10⁶ bytes) per second
Worked example
- 12 TB = 12 × 10¹² bytes.
- 12 × 10¹² ÷ 150 × 10⁶ bytes/s = 80,000 s.
- 80,000 ÷ 3,600 = 22.22 hours.
Rebuilding a 12 TB drive at 150 MB/s takes about 22 hours.
What the result means
If the rebuild takes days, consider RAID 6 or triple parity so a second failure during the rebuild is survivable, and keep a hot spare so the rebuild starts at once.
Assumptions and limits
- The rebuild rate stays constant from start to finish.
- Production I/O, controller rebuild-priority settings and SMR drives can make real rebuilds several times slower.
Questions
Why is my rebuild slower than the drive’s rated speed?
Controllers throttle rebuilds to keep the array responsive, and every surviving drive must be read in parallel. Random-access workloads during the rebuild slow it further.
Does a RAID 10 rebuild faster than RAID 5?
Usually: RAID 10 copies from one mirror partner, while RAID 5 and 6 read all surviving drives and compute parity.