expansion or second NAS?

[Enquiries]

Hello, I currently have a DS918+ that is almost full, though I got it only three years ago. I originally put in four 12TB helium drives using Synology's RAID. I just bought four brand new helium drives that are 18TB each. Now I am faced with a dilemma. Do I buy a DS920+ so to have two NAS (one for backup)? Or do I get a fifth drive plus the expansion unit to expand the existing RAID? Or do I swap out the 12TB disks one by one and replace them with the 18TB drives? And how long would that take to rebuild each drive, and is it safe? There are many related questions here, for example - maybe it's better to copy all my files to a new NAS in RAID 0 (faster and more storage) and use the old NAS as a backup, also in RAID 0. I am aware that the life of a hard drive is on average six years, so the old NAS should be OK for a few years more. What would you do? THANK YOU!

[ed]

Having a backup is certainly the best idea. You can also link both NAS together in order to access the data via a single connection. Having an expansion unit might cost similar to a new NAS. This is why people don't buy them. Having two NAS systems will allow you to set up remote backup tasks. So both NAS can backup up certain folders to each other automatically. This way you keep your data safe and accessible, while also having more storage space.

I hope this helps.