The knowledge base says rebuild time depends on storage size, workload, and drive condition.
What it says:
- If other services are running, a rebuild can be much slower.
- If no other services are running, it is faster.
- Estimated times from Synology’s KB:
- 10,485,760 MB at 10 MB/s = 1,048,576 seconds = 291.27 hours
- 10,485,760 MB at 50 MB/s = 209,715.2 seconds = 58.25 hours
- The estimated time will be affected if any drive is in poor condition.
- The more services run concurrently, the slower it becomes.
- For RAID type changes with the minimum required number of drives, the process becomes less efficient and can take significantly longer.
Safe ways mentioned to speed it up:
- Temporarily adjust the RAID resync speed setting to speed up the process. The KB says the estimates are based on RAID resync speed set to Lower the impact on overall system performance.
- To optimize performance during rebuild, reduce concurrent workloads as much as possible.
Also, one Synology document notes that for performance improvement in general, Synology SSD Cache can reduce I/O latency, and high-speed NICs or Link Aggregation can improve network performance, but that is not specifically a rebuild-speed fix.
If you want, I can summarize the relevant exact KB notes into a short checklist.
Sources used: [3], [9]