Upgrade from single disk to mirror

[eSALTS]

I'm currently running Nas4Free with one 3TB WD Red disk. I am planning on buying another identical disk, and would like to add it to my zpool as a mirror. Is this possible to do without destroying my zpool and creating another? If so, how would I go about accomplishing this?

Thanks in advance.

[eSALTS]

I just read through the ZFS Handbook (I probably should have done that before posting, my bad!). I see I can use "zfs attach".

I'd like to clarify the usage for zfs attach, though.
My zpool is named Data.
My vdev is named Data_disk_0

so I would do "zpool attach Data Data_disk_0 ada1" (replacing ada1 with whatever the id of the new disk is). Is this correct?

[substr]

It usually looks more like zpool attach Data ada0 ada1 , but trying your example wouldn't cause any harm.