Adding Disks to an existing TRAID pool TOS 5.1.34

[YoYoYo]

Hi,
i have an F4-421 with 2 disks 4tb, with a total usable capacity of around 4 tb configured in Traid with data protection (1+1).
Those 2 disks are full of data and i would like to add other 2x4TB HDD to create a 3+1 configuration with a total capacity of around 12tb.
I read that i have to add 1 disk at the time, but what is not clear to me is if i have to use "Add hard drives to the raid" or "Online raid capacity expansion" (option 2 or 4) when i edit the storage pool.
My goal is to have a single volume with 12Tb adding 2 disk capacity to the existing volume without losing any data.
Thanks for your support

[TMroy]

Please pick "Add drive to the raid".

[YoYoYo]

My confusion start on the Traid announcement:
2. Increase the number of hard drives.
Operation method: Keep the TNAS powered on, insert a new hard drive, go to Control Panel > Storage Management > Storage Pool > Edit, and select “Expand”. Make sure that the newly added hard drive meets the requirements and you have enough spare disks slots.

Do you confirm that i have to use add drive and i'll will not lose the data ? Basically the 2 hdd that i will add are from another nas that i'm replacing so i will not have a bkp during this phase...

Which are the difference for those 2 options ?
Thanks again

[TMroy]

No, the drive you add to RAID will sync to other drives, this means you will lose data on this drive. Back up your data before you do that.

I will double check again about the Mode, will come back to your soon.

[YoYoYo]

Many thanks, i wait your feedback before doing it.
Thanks

[YoYoYo]

Adding another info.
The old nas and new f4-421 have the same data. I copied everything from the old one to the new one but i want to move from the old nas, the old disks to add those in new F4-421 to create the 3+1 config (the 4 disks are all ironwolf 4tb, same model).
I'm expecting to lose the data only on the drive that i'm moving from the old nas.
Am i correct?

[TMroy]

Hereby I confirm that for TRAID you only need to pick "Add drive to the raid".

Again, the drive you are going to add to a raid all data on it will be erased. You need to back up data before you do that.

[YoYoYo]

Thank you,
last question, can i copy files in the volume while it is syncronizing ?

[TMroy]

Yes, you can. but it will be very very slow.

[YoYoYo]

Thank you.