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Storage: Directory Structure

RavenDB keeps all data under the location specified by the DataDir configuration value.
In this page:
- On-disk Data Structure
- Voron Storage Environment

On-disk Data Structure

<data-dir>
- Databases
  - <database-name>
    - Confguration
      - Journals
      - Temp
      - Raven.voron
    - Indexes
      - <index-name>
        
        Journals
        
        Temp
        
        Raven.voron
      - ...more indexes
    - Journals
    - Temp
    - Raven.voron
  - ...more databases
- System
  - Journals
  - Temp
  - Raven.voron

The main <data-dir> contains:
- Databases folder
  Contains subdirectories with data per database.
- System folder
  Stores cluster data & server-wide data such as shared resources needed by all cluster nodes,
  e.g. the Database Record.
The System folder, the Database folders, and their inner folders (the Configuration folder and each Index folder) are each a separate Voron storage environment.

Temp Folder

Holds temporary scratch & compression *.buffers files.
These are small memory-mapped files that keep separate data versions for concurrent running transactions.
Data modified by a transaction is copied into the scratch space - modifications are made on a copy of the data.
Compression files are used to compress the transaction data just before writing it to the journal.
When a transaction is written from these files to the journal file it is considered committed.

Journals Folder

Contains Write-Ahead Journal files (WAJ) that are used in the hot path of a transaction commit.
From the journals, transactions will be flushed to the Voron data file where they are persisted.

Entries written to these files use unbuffered sequential writes and direct I/O to ensure a direct write that bypasses all caches.
Writes to the journals happen immediately, have high priority, and take precedence over writes to the Voron data file.

Data is cleared from the journals once it is successfully stored in the data.
The journal's transactions take part in database recovery - info is used to recover up to the same point you were at before failure.

Raven.voron file

This file contains the persisted data on disk.
It is a memory-mapped data file using buffered writes with random reads and writes.