A nice brief post here. This is the operation required to increase disk size when using Linux RAID e.g. mdadm on an underlying ESXi host.
Increase the size of the VMDK files within ESXi
Simply edit the size of both disks within ESXi. In my case they are a combined 1.4 TB being increased to 1.5TB
Restart the machine
Update the size of the mdadm array
sudo mdadm --grow /dev/md0 --size=max mdadm: component size of /dev/md0 has been set to 1610481664K
Grow the partition
sudo resize2fs /dev/md0 resize2fs 1.42.13 (17-May-2015) Filesystem at /dev/md0 is mounted on /Media; on-line resizing required old_desc_blocks = 90, new_desc_blocks = 96 The filesystem on /dev/md0 is now 402620416 (4k) blocks long.
That is all you need to grow the existing virtual disks into the free space you have on the underlying physical disks.
Expanding Linux Raid ESXi