Should I buy a second NAS?

My synology ds215j with 2tb (raid 1) is almost full.

I have a 2tb HD sitting in my drawer unused and was going to buy a dsj216j and another 2tb HD, cost around £230 for both and then that will gve me another 2tb NAS space.

Not sure if this silly, I could buy 2x 4tb HD and transfer the data somehow.

I like the idea of two NAS, seems safer, so I can keep really important stuff on both NAS.

Anyway is it possible to pull one drive from a 2x2TB synology NAS, insert a bigger drive , say 4tb, let the data be synced, then pull the other 2tb drive and insert another 4tb drive, finally leaving it 4tb raid 1?

Another thing swaying me is the cost 2 x 4tb HDD is going to be £260. But I can hen sell the old 2tb drives I guess.

Have you considered selling your 2 bay NAS and getting a 4 bay?

Yes, you can do what you've described.

You can disconnect drive 2, connect up a new drive, then once that has the data, disconnect drive 1.

It may take s while for the data to replicate.

You could buy a separate USB RAID enclosure and attach it to the NAS. I have this one: http://www.icydock.com/goods.php?id=189