I have a software RAID-5 made up of 3 drives, call them A,B,C. I would like to replace the old C drive with a newer and larger-capacity one to eventually expand the array. This is on an Ubuntu 16.04 system running mdadm to manage the drives.
Online searches recommend taking drive C offline by setting failing mode, remove it from the array, add a new drive D and let the array resync. I worry that while the resync process is happening (on the order of a day for a 1.5 TB drive) the array is fragile and could be lost if drives A or B fail.
Is there a way to instead, add a new drive D to the array and let it 'mirror/sync' the contents of drive C first and then just fail/remove drive C in such a way that the array does not need to resync?
Note: I edited some of the terminology to clarify the issue thanks to the comments