Nowadays thats less than 10 drives. I literally just ordered 10 20 tb drives to fill my second nas.
I have two synolygy 1019+ with ds 517 expansion units. That 10 drives for each set. Technically i could set that up to have about 400 tb usable.
I buy factory recertified drives for about 200 ea. with a couple spares.yea its a chunk of change but not too crazy.
I have multiple friends with more than a pb.
Factory refurbs. I have 3 nas boxes full of drives from there. No issues
I have a perfectly functional ds416 but its old too. I bought a newer model as my 416 mirrors data to it. Its a backup of my backup.
The main reason i did it is support for future updates including security patches. The 416 doesnt autoipdate anymore i have to dl a seperate file and update. Im concerned how much longer it will get security patches. When it goes end of life i can easily make the newer box my main nas. Ill probably do it next year regardless.
Been running factory refurbished. Thats the important part. It must say factory refurbs. Ive had one failure in 5-6 years and was warranty replaced