Creating RAID1 volume without formatting old disk

I have a My Cloud EX2 Ultra with a 4TB RED disk, with some data (about 2.5 GB).
I want to add a second identical disk and use a RAID1 system to have a mirror backup of first disk, can I do it without having to format the first disk and loose any data on it?
Thanks in advance for your help

Whenever a RAID is changed, it wipes out all the drives to create the new RAID. In your case, one suggestion would be to use the JBOD option. Use the two drives as separate volumes and run and internal backup of the shares on Volume 1 to Volume 2 on the new drive. The other option, since there is only 2.5 GB,(not sure if you meant 2.5 TB), copy the 2.5GB off the drive, build the RAID 1 and then copy the data back over.

Thanks for your reply.
Indeed, I meant 2.5 TB, and I don’t have another big HDD to backup my data on it…
So you mean that the alternate way would be a software backup, not hardware ? Is it safe, considering that the NAS regulary checks the HDD health?

The internal backup is built in software. It can be scheduled for your needs. The drive also has built in diagnostics and tests that can be run on the drives as well as the drive’s Operating System.

OK I noticed I have 2.31 TB left, and 1.26 used.
If I copy the data on a 1TB external HDD (plugged in the USB port of the NAS, for example), completed with 300 GB on my local PC, can I be sure that no data will be corrupted ? If so, what are the steps:

  1. Copy the backup data
  2. Open the NAS, plug the new 4 TB HDD
  3. Go to settings, configuring RAID1 for both HDD, that will format them and erase any data
  4. Copy the backed up data to new created volume, and they’ll be automatically stored in both HDD in a ‘mirroring’ way.

Am I right ? Did I miss some step?

That sounds right. Just verify the data that you copied off the drive before you create the new RAID. I have seen people create “shortcuts” rather than copy the actual data.

Thanks for your help; I’ll try to do it this week and hope that i’ll be able to keep all my data!