I've been using an mdadm RAID1 array with 2 2TB disks for a few years without issues.
Recently I needed to upgrade it to 4TB so I bought 2 new disks of 4TB and plan to replace one, wait for the rebuild, then replace the other, grow, and to finish resize the filesystem in /dev/md0
The problem is that, in all these guides, the disks are partitioned before being added to the array (usually 1 single partition taking all disk), and I found that it's a common practise, but my disks were added to the array on its day without partitions, i.e.(one of my disks in the array):
Disk /dev/sdb: 1,8 TiB, 2000398934016 bytes, 3907029168 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disklabel type: dos Disk identifier: 0x000059b8
So, the question is: is it really required to pre-partition a disk that will be used in a mdadm RAID1 array? is there any advantage on doing it?