How to attach persistent disk on running instance at Google Compute

So I have this USD300 credit for two months period to play around with Google compute.

I had created an instance, but with very small storage, 10GB. Then I decide nothing much can be done with that, so I created a persistent disk.

Google compute's documentation is incomplete and terrible, so we need to do try and error. So this is the confirmed workable solution that I tested:

Let say we created a project name "blah-1234"

and a persistent disk name "disk-for-blah"

to be attached to a VM instance named "vm-blah"

Please replace the --zone

~$ gcloud compute instances attach-disk --project "blah-1234" vm-blah --disk disk-for-blah --zone asia-east1-c

If everything is fine (it'll take few seconds for the disk to be attached. You'll be prompted with the following output) :

Updated [https://www.googleapis.com/compute/v1/projects/blah-1234/zones/asia-east1-c/instances/vm-blah].

memory of nobody