Question:
So we have people on one hand saying 1TB or some more, and then on the other end you're saying 100PB(?!). Whose estimate is closer to reality?
If it actually is in the 1-2TB range I think that's pretty manageable to be honest. Most people want to use thin clients anyway.
Reply:
Bitcoin is at 60,000 tx per day and I think Visa + Mastercard is 6,000 per sec. So multiply the 10GB for Bitcoin blockchain by 8000 (= 80 Terabytes) just to get to current commerce. And Visa + MC don't do micro transactions. With micro transactions we would be in the Petabyte range.
So even if your bloat is only a constant factor less than an order-of-magnitude, the real problem is one-time ring signatures defeat the mini blockchain design (because you can't know which address has which balance with ring signatures).
Edit: I think there is some effort underway looking into how to prune the Bitcoin blockchain, but afaics this won't be possible with ring signatures because you don't know which inputs were spent. There are some heuristics that could be applied, but it looked very messy when I thought about it a bit. One of the mixed inputs not spent can cascade and prevent the pruning of all those mixed with.
If that is true, then the units might not be rare but blockchain space might indeed be very scarce (and then must be somewhat expensive). It is a useful perspective.
At 8 billion people and 1024 account balances each, and say 128 bytes per account storage, that is 1 Petabyte. That is the best the mini blockchain could do. One-time ring signatures would make it entirely intractable (100s or more of Petabytes) unless you increase the cost until the 8 billion are restricted.
Let's assume a 10 year goal of 1 billion x 8 account balances each, so 1 Terabyte which is one hard drive. And hard drive space doubles every 18 months, so in 17 years we can store 1 Petabyte on one hard drive. So the mini blockchain can scale.
So there is no scarcity, except
for badchosen design (priorities).
P.S. we do have to discourage dust balances though.
To get to Visa scale with Bitcoin brings us to 80 Terabytes without pruning.
Monero claims 5 - 6x bloat (and I disputed that, it could be higher see below...). So heading towards a Petabyte just to reach Visa+MC scale.
And we are expecting micro transactions and crypto-economies (Ethereum, CounterParty, Bitshares, etc) so the volume of transactions could increase orders-of-magnitude over Visa+MC scale.
Wait a minute, 6MB/day with 3% of Bitcoin transactions, and Bitcoins blockchain grows at 34 MB/day, that's not 5x the growth of blockchain compared to bitcoin, it's 5.82x, closer to 6x for the same number of transactions. You want to tell me that 6x bigger blockchain is not a design flaw...
As I wrote upthread, I don't think that 5 or 6x calculation is accurate. Because someone told me that Monero currently has a limitation wherein you can't mix too many inputs (incorrect?), so you need to mix multiple times to achieve the same level of mixing you would with one transaction without the limit. Thus many of the transactions are multiple mixes for the same transaction, thus the real bloat is orders-of-magnitude higher than Bitcoin.
But remember from upthread discussion between smooth and myself, that the level of that multiplier is less relevant. I explained (argued) that the real problem is one-time ring signatures make the blockchain unprunable.