codex-research/evaluations/rollups.md

Ethereum L2 Rollups

A quick and dirty overview of existing rollups and their suitability for hosting the Codex marketplace smart contracts. To interact with these contracts, the participants in the network create blockchain transactions for purchasing and selling storage, and for providing storage proofs that are then checked on-chain. It would be too costly for these transactions to happen on Ethereum main net, which is why this document explores L2 rollups as an alternative.

Main sources used:

• individual websites of the rollup projects
• https://l2beat.com
• https://blog.kroma.network/l2-scaling-landscape-fees-and-max-tps-fe6087d3f690

Requirements

For the storage marketplace to work, we have the following requirements for a rollup:

1. Low gas costs; if gas is too costly then the business case of storage providers disappears
2. EVM compatibility; this shortens our time to market because we already have Solidity contracts
3. Support for BN254 elliptic curve precompiles (ecAdd, ecMul, ecPairing) for the proof system
4. High throughput; our current proof system that checks all proofs separately on chain requires a large number of transactions per second
5. Censorship resistant; an L2 operator should not have the power to exclude transactions from certain people or apps

Note that low latency is not a requirement; it's ok to have latency equivalent to L1, which is in the order of tens of seconds.

Main flavours

Although there are many L2 rollups, there is a limited number of technical stacks that underly them.

There is the family of purely optimistic rollups, that rely on fraud proofs to ensure that they are kept honest:

• Arbitrum
• Optimism / OP Stack
• Fuel

And there are the rollups that rely on zero-knowledge proofs to prove that they act honestly:

• Polygon zkEVM / CDK
• Linea
• zkSync
• Scroll

And there's Taiko, which uses a combination of zero-knowledge proofs and fraud proofs to keep the network honest:

• Taiko

Gas prices

A rough approximation of average gas prices for submitting a Codex storage proof for each rollup:

Rollup	Average proof price	Potential profit
Mantle	$0.0000062723	$2.58
Boba network	$0.0016726250	-$2.54
Immutable zkEVM	$0.0073595500	-$20.01
Arbitrum	$0.0083631250	-$23.09
zkSync Era	$0.0209078125	-$61.63
Base	$0.0418156250	-$125.86
Optimism	$0.0836312500	-$254.32
Polygon zkEVM	$0.1254468750	-$382.77
Blast	$0.1672625000	-$511.23
Scroll	$0.2090781250	-$639.69
Taiko	$0.2508937500	-$768.15
Metis	$0.4014300000	-$1,230.59
Linea	$0.8363125000	-$2,566.55

This table was created by eyeballing the gas cost and token price graphs for each L2, and calculating the USD costs for a proof from that. We did not include rollups that are not EVM compatible.

Potential profit (per month per TB) is calculated by assuming operational costs of $1.40 and revenue of $4.00 per TB per month, an average slot size of 10 GB, and an average of 1 proof per slot per day.

EVM compatibility

This shows which rollups are EVM compatible, and whether they support the BN254 elliptic curve precompiles that we require for verification of our storage proofs (ecAdd, ecMul, ecPairing).

Rollup	EVM compatible	Elliptic Curve operations
Arbitrum	Yes	Yes
Base	Yes	Yes
Blast	Yes	Yes
Boba network	Yes	Yes
Immutable zkEVM	Yes	Yes
Linea	Yes	Yes
Mantle	Yes	Yes
Metis	Yes	Yes
Optimism	Yes	Yes
Polygon zkEVM	Yes	Yes
Scroll	Yes	Yes
Taiko	Yes	Yes
zkSync Era	Yes	No
Fuel L2 V1	No	N/A
Fuel Rollup OS	No	N/A
Immutable X	No	N/A
Polygon Miden	No	N/A
Starknet	No	N/A
zkSync lite	No	N/A

Throughput

A rough approximation of the maximum number of transactions that a rollup can handle, and the maximum size of the storage network that it might support:

Rollup	Maximum TPS	Maximum storage
zkSync Era	750	1236 PB
Starknet	484	798 PB
Optimism	455	750 PB
Base	455	733 PB
Mantle	400	659 PB
Metis	357	588 PB
Polygon zkEVM	237	391 PB
Arbitrum	226	372 PB
Boba network	205	338 PB
Scroll	50	82 PB
Taiko	33	54 PB
Blast	?	?
Immutable zkEVM	?	?
Linea	?	?
Fuel L2 V1	?	?
Fuel Rollup OS	?	?
Immutable X	?	?
Polygon Miden	?	?
zkSync lite	?	?

Maximum size of the storage network is calculated assuming an average 1 proof per 24 hours per slot, average slot size 10 GB, and average erasure coding rate of 1/2. In practice the calculated maximum storage is going to be less, because we can't use up the entirety of the rollup capacity.

Maximum TPS figures are taken from an overview document by Kroma

Censorship resistance

Censorship resistance can be achieved by having a decentralized architecture, where anyone is allowed to propose blocks and there are are no admin rights that allow a rollup operator to change the rules in their favour.

Only Fuel L2 V1 has all these properties, the others don't. And because Fuel L2 V1 is a payment network without smart contracts it is not suitable for the Codex marketplace. This means that at this moment there is no censorship resistant rollup that can host the Codex marketplace.

Taiko is one of the few rollups that has a decentralized architecture, and it's committed to becoming permissionless. However, at the moment it is not.

Rollup	Decentralized	Permissionless	Adminless
Fuel L2 V1	Yes	Yes	Yes
Metis	Yes	No	No
Taiko	Yes	No	No
Arbitrum	No	N/A	N/A
Base	No	N/A	N/A
Blast	No	N/A	N/A
Boba network	No	N/A	N/A
Fuel Rollup OS	No	N/A	N/A
Immutable X	No	N/A	N/A
Immutable zkEVM	No	N/A	N/A
Linea	No	N/A	N/A
Mantle	No	N/A	N/A
Optimism	No	N/A	N/A
Polygon zkEVM	No	N/A	N/A
Polygon Miden	No	N/A	N/A
Scroll	No	N/A	N/A
Starknet	No	N/A	N/A
zkSync lite	No	N/A	N/A
zkSync Era	No	N/A	N/A

Conclusion

There seems to be no rollup that matches all the requirements that we listed in the beginning of the document. The most pressing problem is that only Mantle seems to be cheap enough to allow storage providers to turn a profit, given the assumptions of an average 10 GB slot size and 1 proof per 24 hours. It is unclear whether these low prices are sustainable in the long run. If we want to have more choice on where to deploy, then we either need to reduce the number of on-chain proofs in Codex drastically, or we need to find a way to reduce rollup transaction costs.

Luckily we're already working on reducing the number of proofs by introducing proof aggregation, but the analysis in this document shows that we might not be able to launch a storage network without it. Reducing the number of proofs also ensures that the network can grow to a larger total size.

When we look at reducing the transaction costs, then the best thing to focus on is getting rid of the need to post transactions on L1 in blobs. This is by far the most expensive part of running a rollup, and this is most likely also why Mantle is the only rollup in this overview that is cheap enough; it uses EigenDA instead of posting to L1. In this respect, it might also be interesting to look at Arbitrum AnyTrust, which has a similar design. We could also consider creating a fork of an existing rollup and use Codex as the DA layer. Some of the new modular architectures for creating rollups, such as Espresso, Astria, Radius, Altlayer and NodeKit could also make it easier to experiment with different rollup designs.