> For the complete documentation index, see [llms.txt](https://docs.lumia.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.lumia.org/ecosystem/lumia/architecture/data-availability/where-lumia-transaction-data-lives.md).

# Where Lumia transaction data lives

**Who this is for:** developers and issuers who want to know what actually holds Lumia's off-chain transaction data. **You should already know:** [Validium](https://app.gitbook.com/s/chmhPiVNAafGw48c4oU2/ecosystem/lumia/architecture/data-availability/validium).

### What holds Lumia's data

Avail is named as the network's data-availability provider for its validium mode: the layer that holds the transaction data behind Lumia's validity proofs, rather than posting that data directly to Ethereum.

### How that network works

Avail is a modular data-availability network: a blockchain purpose-built to do one thing, which is guarantee that data submitted to it is genuinely retrievable, without also executing any application logic itself. It uses data-availability sampling and polynomial commitments so that a light client can check, cheaply, that a large amount of data is available without downloading all of it. That's a different, cheaper trust model than "download everything yourself" or "trust a small fixed committee of signers."