Do I start buying 8TB archive drives or not?

[Chris Downs]

The time has come for more space in my Plex server...

At present, it has three 4TB drives (just consumer grade). I was going to stick to 4TB drives (or maybe the 6TB WD reds), but "upgrade" to NAS versions, but I've been wondering about the 8TB archive drives from Seagate. Has anyone been using them for a decent amount of time with Drivepool?
In theory they seem ideal for a Plex server, mostly used for reads.

 

They also seem very good value in cost/TB. I reckon I'm using space at a rate of about 3.5 to 4TB per year now. A 4TB drive is about £109 at present. The 8TB is £178, which is £89/year if I assume 4TB/yr. It's clearly better value.

However, I do wonder about whether the archive drives are suited to a system that can either run continuously, or be powered up and down fairly regularly (it varies but once a day is usual). 
I welcome thoughts and advice on this!

[Umfriend]

As I backup my Server to those Archive drives, I can tell you that having been written to once does not mean you get hit by the write penalty. Somehow, the HDD does track what is occupied and what is not and if you can get sequential writes to clean tracks then it writes like crazy as well (for a spinner).

 

On the other hand, if it gets filled up and needs to replace a lot, then it really kills. I have had Server Backups that took somewhat over 24 hours for little over 4TB of data.