Request for Comment: Adding 6TB drives to RS815

[Biggupp]

Present setup on RS815:
2x2TB hd's RAID 1 ext4
1x2TB hd for external USB Backup

I am a professional photographer and am nearty at capacity and need to expand by adding hd's. What do others suggest? I purchased 3x6TB hd's. I am thinking of creating a second, 6TB RAID 1 ext4 and using the third 6TB as backup.

I'd like to use my old DS211j 2-bay NAS for local backup using 1x2TB and 1x6TB for their respective size arrays.

Lastly, I am researching offsite backup and wonder others do. How good is Synology's backup service?

 

[Biggupp]

Based on the good feedback here, I opted to create 2 x RAID 1 arrays:
2x2TB (existing)
2x6TB

During the install of the 6TB array, which went fine, I discovered that the 2TB drives (Vol 1 and Vol 2) were not functioning as RAID 1. IE, each contained different data. Not sure what happened; drives are identical and were originally set up as RAID 1.

I moved data from Vol 1 to the 6TB array so that I could wipe Vol 1 in order to (re)create the 2TB RAID. I used Vol 2 as the source volume to mirror. FYI, I purchase multiple drives at the same time so that RAIDs contain identical drives.
I followed the procedure to repair the set, starting with removing / reinserting Vol 1 to show a degraded drive in Storage Manager. After repair (an 8hr sync), the 2 TB RAID 1 only shows 1TB, half of what it should be!

What did I miss in this procedure?

 

[Biggupp]

I figured it out. In Storage Manager > Volume > 'Volume 2' , selecting 'edit' opened a dialog in which I could change 'allocate size (GB)'. Changed it to reflect the full 1.8TB! Not sure why the default was half the max size. But voila!