Hi all, long time listener first time caller,

I have a WD PR4100, old equipment but it suits my needs, I maxed out the ram when I first bought it 5 years ago and it has 4 drive bays. Right now I have four 4TB WD Red Pro/Premium drives inside in a RAID1 setup. One of the drives is more recent and the other 3 are from when I bought the PR4100 5 years ago.

It is time for me to replace the drives, one started failing awhile back and that is why it was replaced, but in anticipation of the other 3 failing eventually I would like to upgrade them all and to take this opportunity to replace them with higher capacity drives.

First question, is there an upper limit for capacity on the PR4100 and can I just drop new 20tb+ drives in there and expect them to work?

Second question, do I replace them one at a time and in doing so would the system rebuild the RAID 1 setup or is there a better way?

This is for local backups and a self-hosted media library, not commercial or professional use.

I am not looking to build a new NAS system right now as the PR4100 is working as intended without much hassle but in a year or so I may need a more complex and professional NAS/server depending on if I get back into video production more fully.

Thank you for your time and for everyone posting and providing help in this community.