Is it safe to write data to a RAID 6 while it's rebuilding?

Solution 1:

IO time will be consumed by the operations which will be time not available for the rebuild, slowing things down slightly, but it's definitely safe to write to the array while rebuilding.

Solution 2:

Yes, you can write data to the array while it rebuilds. There is always an impact when writing data to the array but it shold be minor.

Solution 3:

Writing whilst rebuilding should not decrease your chances of a succesful rebuild.
You will however notice a slight performance decrease during the rebuilding, because the controller needs some of its bandwidth to rebuild the array.