A common Snapshot for "Snapmirror resync -S"?

[netappmagic]

As understand, when I run "Snapmirror resync -S", there has to be a common Snapshot between two sides.

The SS I have on both side has same name, but different size.

Are these two SS's considered to be the common, and if yes, whey they got different size?

Thanks for sharing! 

[netappmagic]

Can somebody please share your thoughts SOONER? Appreciated!

the following are two commands to fail back:

pr::>snapmirror resync -S -source-path dr-cluster://vsm1/vol1_mirror -destination-path pr-cluster://vsm1/vol1

pr::>snapmirror update -S -destination-path pr://vsm1/vol1 -source-path dr-cluster://vsm1/vol1

My second question:

by running above 2 commands, will updates made on DR site be copied to PR site?

[netappmagic]

Then:
... Break...

Correct?