Also you must factor in the following:
As you already know if you create another vdev using three more 2TB drives you would end up with a 3.6TB RAIDZ1 pool. The down side to this is you have only gained 3.6TB of storage and you still retain protection for a single drive failure of each pool. Total storage is 7.2TB
I wish you would have answered my question about how much data you currently have stored as this is a factor in giving you good advice but lets assume you can back this up and destroy your current pool. You could add three more 2TB drives and create a pool as a RAIDZ2 which allows for two drives to fail and you still have a safe system and you still have 7.2TB of storage but under one pool. Lets take those same drives to a RAIDZ1 and you end up with 9.1TB of usable space but only with a single drive failure of protection.
I'm not sure how safe you want your data but we do try to push RAIDZ2 if there is any important data or the recovery of the data is something you don't want to deal with. I started out with four 2TB drives in a RAIDZ1 and ended up with six 2TB drives in a RAIDZ2 and am very happy with that arrangement.
Now lets explore a third option... Lets say you are not able to backup all your data but really want to just double your storage space easily. Well you could purchase three 4TB drives and using the manual, replace each drive one at a time and let it resilver each drive before continuing. The risk is if you screw up you loose all your data. The reward is after you install the third 4TB drive your pool will automatically double in size. Now you have doubled your pool size and you have three 2TB drives in which you can manually wipe clean and then use to create another pool of three drives if you want.
There are a lot of options but you need to figure out what you want your system to do.
-Joe
hi and thanks for the reply
I currently have about 1 tb left and am wanting to plan ahead since in a few months that 1tb will run out.
To be honest I didn't realise that freenas was so technicaly demanding for a newcomer.I might have reconsidered if i'd known.
I did some research and all the videos I saw on youtube were saying quite flippantly that Freenas is so cool, its easy to set up and this is how you do it blah blah blah.
What none of thee videos tell you is that to properly administer you system you have to learn a lot about freebsd, RAID ,command line etc.
Anyway, i'm here now .
To answer your question, I could in theory back up my data on a couple of USB hdd and.create one zpool.
Replacing each 2tb drive with a 4tb drive sounds like a recipe for disaster as Im sure something will go wrong.
From an ease of use perspective, creating a new zpool seems like the easiest option to me.