Upgrading disks in a RAID1 Synology 2-bay drive
The solution is still applicable, even if you're using RAID1 instead of Synology Hybrid RAID (SHR). The only difference if you're using RAID1 is that you'll need to upgrade both drives, and keep them equal in size in order to maximize disk space.
As you mentioned you're using a 2-bay system, it won't make any difference anyway; the real benefit of SHR is when you're using 3+ disks, as they can be of different sizes and still minimize the wasted disk space.
Basically the procedure to upgrade a Synology is:
- Unplug one of the disks and keep it in a safe place, in the case something goes wrong
- Plug a new 3TB disk, and wait for it to rebuild the RAID1 (note it may take several hours, depending on model and much data you have)
- Unplug the old 1TB and plug the second 3TB
- Wait for the RAID1 to be re-built again
- Go to Storage Manager and increase the volume size to 3TB (update: newer DSM versions do this automatically)
Done!
You still have a copy of your data on the 1TB disks, so if anything goes wrong, you can still recover the data manually. If that happens, it is strongly recommend that you do a full disk copy sector-by-sector (using dd on a Linux machine, or a tool like CloneZilla) before attempting recovery.
Despite the name, the Synology Hybrid RAID technology is not really proprietary to Synology. It's just some clever use of Multiple Device (MD) and Logical Volume Manager (LVM2). So if you have an emergency, you can still plug the drives directly to a Linux machine and have fun using md/lvm. Both LVM and MD are open, stable, well documented and widely adopted.
According to Synology's documentation this drive support their (I assume proprietary) Synology Hybrid RAID which according to this document allows you to replace one 1 TB drive with a 3 TB drive, then once the data is replicated to the new drive you can then replace the remaining 1 TB drive with the new 3 TB drive and the system will automatically expand out to 3 TB.
Of course, if it screws up, you could be SOL (of course you would have the first 1 TB drive that you removed).
The safest bet (IMHO) would be to either borrow or purchase a standalone 1 TB drive, backup your data to this 1 TB drive, re-init your NAS with the new 3 TB drives and then restore.