```{eval-rst}
.. _explanations-drive:
```

# Drive

## Overview

Using the traditional, layer 1 blockchain for data storage is widely known to be expensive and inefficient. Consequently, data for Dash Platform applications is stored in Drive, a layer 2 component that provides decentralized storage hosted by evonodes. As data changes over time, Drive maintains a record of the current state of each item to support easy retrieval using [DAPI](../explanations/dapi.md).

## Details

### Drive Components

There are a number of components working together to facilitate Drive's overall functionality. These components are listed below along with a brief description of service they provide:

- [Platform chain](../explanations/drive-platform-chain.md) (orders state transitions; creates and propagates blocks of state transitions)
- Platform state machine (validates data against the [Dash platform protocol](../explanations/platform-protocol.md); applies data to state and storage)
- [Platform state](../explanations/drive-platform-state.md) (represents current data)
- Storage (persists the current state - identities, data contracts, documents, etc.)
- GroveDB (authenticated hierarchical storage backend enabling cryptographic proofs returned via [DAPI](../explanations/dapi.md))

### Data Update Process

The process of adding or updating data in Drive consists of several steps to ensure data is validated, propagated, and stored properly. This description provides a simplified overview of the process:

1. [State transitions](../explanations/platform-protocol-state-transition.md) are submitted to the platform via [DAPI](../explanations/dapi.md)
2. DAPI relays state transitions to the platform chain's consensus engine (Tenderdash), which asks the platform state machine to validate them  and speculatively execute them when building or verifying a block proposal
3. The block is propagated and voted on by validators
4. Once the block is committed, each node finalizes it — persisting the speculative state changes to Drive, or executing the block if it was received via sync

```{eval-rst}
.. figure:: ../../img/drive.svg
   :class: no-scaled-link
   :align: center
   :width: 80%
   :alt: Storing data in Drive

   Storing data in Drive
```

```{toctree}
:maxdepth: 2
:titlesonly:
:hidden:

drive-platform-chain
drive-platform-state
```