Linux mdadm recovery speed inquiry

[lightp2]

Hi, to understand recovery speed, I tested the following

1. Test inside Linux VM. 1-CPU and 1GB RAM
2. 6 units of 2GB dedicated virtual disks for RAID-6 testing.
3. mdadm RAID-6 built using the 6 virtual disks.
4. I test failed 2 of the virtual disks.
5. Then waited for a while, re-added them back to RAID-6.
6. Un-scientific, it took between 1 to 2 minutes to re-sync everything back to normal.

Question
1. How to calculate exactly the RAID-6 disk recovery speed in this particular instance? To make it easy, say it took roughly 100 seconds.

Exactly how much data is read/written to recovery back to normal?

 

[XOR != OR]

Disk rebuilding is a low priorty task in linux, so the speed will be variable depending on the load on the system. To get an idea though, watch /proc/mdstat while the array is rebuilding. This will give you raw throughput as well as estimated recovery time.