I've been looking to get a large storage drive and decided to just get a NAS. Wanting to get a manufacturer re-certified for the extra saving, but between all the drives ServerPartDeals has, which are basically just all Exos for the re-certified, the sizes and prices don't seem consistent.

I'll say I am quite ignorant on the market as a whole, so maybe there's a reason I don't understand, but I'm looking for clarification so I can try picking the best deal to quality.

For instance, my 1st choice is a 16TB X18 for $199, which seems to be selling based off stock numbers dropping. But then I see a 20TB X20 for $219, only $20 more for 4TB more, but it's been sitting at what looks like max stock with no change.

There's other inconsistently priced ones, but this seemed like the largest confusing values. So, what am I missing that makes this 20TB only $20? That seems quite low of a difference. And why does it seem like it doesn't sell despite the apparently steal price (at least to me 4TB more for $20 more seems that way).