Target size: 8 TB striped across 8 disks (from 2 TB on a single disk).

First off the machine was too small. Resized from E2s_v2 (4 data disks) to E8s_v3 (16 data disks).

Disk creation:

for i in {1..8}; do az vm disk attach -g euwest-db --vm-name dbreplica1 --disk dbreplica1_pgdata$i --new --size-gb 1024; done

[wait for disks to appear; /dev/sdd to /dev/sdk appear]

Create a template with fdisk (single partition, full disk, type=linux raid autodetect (fd)) then duplicate it

fdisk /dev/sdd
for disk in {e..k}; do sfdisk -d /dev/sdd | sfdisk /dev/sd$disk; done

Create a raid between the disks

mdadm --create /dev/md0 --level 0 --raid-devices 8 /dev/sd{d..k}1

Add the raid to the LVM volume

pvcreate /dev/md0
vgextend data-vg01 /dev/md0

Move data from the old PV to the new PV

pvmove /dev/sdc /dev/md0

[in progress...]