Really? I need some new WD Red drives. Was looking at 8 x 8TB drives.......
Last time I bought one was in July. It was a 20TB model, it's normal price then was ~£615
The drives individually were ~£315
I paid about £360 for the MyBook Duo model with 2x10TB's in it.
Drive prices are dropping all the time, at the moment for WD Red's the sweet spot for price per TB is the 10TB models, if you're populating a new NAS I wouldn't buy all 8 at once, just buy what you need now and an extra drive, by the time you need more space odds are they'll be cheaper again.
I’ll be replacing 8 x 2TB drives.
Depending upon your system though do you need to replace them all at once?
I use Synology's Hybrid RAID so I can mix and match drive sizes, the only thing I can't do is replace a drive with a smaller one. Unlike traditional RAID this allows the full size of all the drives to be seen and used.
This of course may not be an option for you.
It’s actually 8 x 3 TB drives i’ll be replacing, but i’ll have to replace each drive, one at a time, then once all replaced, expand my array.
But it will also allow me to migrate data from my 8 x 2TB data and sell those drives. The 3TB drives will then replace another 8 x 2TB drives in another array.
It might be worth sounding one note of caution to check that the NAS enclosure can "handle" the size of drives you anticipate using: Some devices have a "maximum drive capacity" they can accomodate - usually it's cited in the datasheet somewhere.
It's also worth mentioning that if you opt for RAID redundancy as so forth, as the drives get bigger and bigger, the longer the rebuild time is in the event of a failure and the thusly the longer one is "vulnerable" to a second failure (unlikely as it is.) One of many reasons one should still make backups of important data.
(Incidentally, years ago I looked after a SAN that "only" used 500GB drives at a time when 2-4TB was state of the art in order to mitigate rebuild times - though with SAN's with dozens of discs, we tend to have a fair few "hot spares" in the pool!)