Convert from single disk pool to mirror?

Hi, I have Proxmox installed on zfs rpool with only one drive (sda2)
I added an equivalent SSD drive, and my question is how do I convert to mirror?

Note, all the vms are on a different pool.

fdisk /dev/sda
Device Start End Sectors Size Type
/dev/sda1 34 2047 2014 1007K BIOS boot
/dev/sda2 2048 390705549 390703502 186.3G Solaris /usr & Apple ZFS
/dev/sda9 390705550 390721934 16385 8M Solaris reserved 1

rpool ONLINE 0 0 0
sda2 ONLINE 0 0 0

zpool attach poolname singledisk newdisk is the command syntax to convert singledisk from a single disk vdev to a mirror vdev.