# A collection of Celestia-related articles [//]: # (As this list grows it will get separated into more specific sections) This is a list of all the pieces I've written about Celestia and its related topics. If there's anything in particular you'd like to see explored, reach out to me on [twitter](https://twitter.com/likebeckett). 1. [The different types of rollups that are possible with Celestia](https://www.reddit.com/r/CelestiaNetwork/comments/tyman7/different_types_of_rollups_that_are_possible_with) 2. [Secure light nodes and the scalability trilemma](https://www.alexbeckett.xyz/secure-light-nodes-and-the-scalability-trilemma/) 3. [settlement layers in the modular stack](https://forum.celestia.org/t/settlement-layers-in-the-modular-stack/205) 4. [A brief data availability and retrievability FAQ](https://hackmd.io/@alexbeckett/a-brief-data-availability-and-retrievability-faq) 5. [The state growth problem in a modular blockchain ecosystem](https://forum.celestia.org/t/the-state-growth-problem-in-a-modular-blockchain-ecosystem/325) 6. [A glimpse at the multi chain future](https://www.alexbeckett.xyz/a-glimpse-at-the-multi-chain-future/) [//]: # (How modular blockchains sovle the state growth problem - something like that)
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A brief data availability and retrievability FAQ

This is a non-exhaustive list of questions that have come up in Eric Wall's discussions regarding data availability. What is data availability? Data availability refers to the availability of transactions in a block that is appended to the tip of the chain. During consensus, validators download the block to verify its availability. If the block contains any transactions that are withheld by a validator, the block is unavailable and will be rejected as invalid. What is the difference between data availability and what we call data retrievability? Data availability is only concerned about the availability of a block when it is being proposed by a validator. Once the block has completed the consensus processes, is appended to the tip of the chain, and has propagated throughout the network, then the ability to download transactions from that block is what we call retrievability. This distinction is important because retrievability is a different problem from availability. What is the data availability problem? The data availability problem is concerned with the ability for nodes to verify that a block is available. For validators this occurs during consensus. For non-consensus nodes, this occurs when the block has passed consensus and is propagated throughout the network.

4/1/2022
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