Skip to content

SnapRAID Configuration Guide

SnapRAID Official Docs

Overview

SnapRAID is a backup program for disk arrays. It stores parity information of the data to recover from up to six disk failures.

Unlike traditional RAID 5 or 6, SnapRAID is not real-time; it is a snapshot-based system.

  • Provide fault tolerance to protect against (inevitable) hard drive failure
  • Checksum files to guard against bitrot
  • Support hard drives of differing / mismatched sizes
  • Enable incremental upgrading of hard drives in batches as small as one
  • Each drive should have a separately readable filesystem with no striping of data

The Parity Concept

SnapRAID requires dedicating specific disks to "Parity."

  • Parity Level: One parity disk protects against one drive failure. Two parity disks protect against two failures, and so on.
  • Sizing: The parity disk must be equal to or larger than the largest single data disk in the array.
  • Storage: Parity disks contain only the large .parity file; they cannot be used for standard data storage.

Installation

To ensure the latest features and compatibility, SnapRAID is often compiled from source.

Compile from Source

Run the following commands to download, compile, and install version 13.0.

# Download source
wget https://github.com/amadvance/snapraid/releases/download/v13.0/snapraid-13.0.tar.gz

# Extract archive
tar xzvf snapraid-13.0.tar.gz

# Enter directory
cd snapraid

# Compile and Install
./autogen.sh
./configure
make
make check
sudo make install

# Verify installation
snapraid -V

Configuration

SnapRAID is configured via a single text file located at /etc/snapraid.conf. This file defines the parity volumes, content files, and data disks.

Key Components

  1. Parity Files: The destination for redundancy data.
  2. Content Files: These act as the "index" or "database" of the array. They contain checksums and file maps.

  3. Critical: Multiple copies should be stored on separate physical disks (e.g., one on the boot drive, others on data drives) to ensure the index survives a disk failure.

  4. Data Disks: The actual storage drives containing the media/files to protect.

Configuration Example (/etc/snapraid.conf)

Create or edit the file using a text editor:

# --- Parity Location --- 
# The parity file must be on the dedicated parity drive
parity /mnt/parity1/snapraid.parity 

# --- Content files ---
# Store copies on multiple physical drives for safety
content /var/snapraid/snapraid.content
content /mnt/disk1/snapraid.content
content /mnt/disk2/snapraid.content

# --- Data Disks ---
# Assign a name (d1, d2) and a mount point for each disk
data d1 /mnt/disk1
data d2 /mnt/disk2

# --- Excludes ---
# Prevent temporary files from breaking the sync
exclude *.unrecoverable
exclude /tmp/
exclude /lost+found/

Usage & Maintenance

Because SnapRAID is snapshot-based, the array is not protected until a "sync" is performed.

Syncing

Run the sync command to update the parity information. This reads data from the data disks and computes the parity.

snapraid sync
  • Note: The first sync may take several hours. Subsequent syncs only process changed data.
  • Interruptible: The process can be stopped (Ctrl+C) and resumed later.

Scrubbing

Scrubbing checks the data and parity for silent corruption (bitrot).

snapraid scrub
  • Default Behavior: Checks approximately 8% of the array that hasn't been scrubbed in the last 10 days.
  • Custom Plan: To check a specific percentage (e.g., 5%) of blocks older than 20 days: 
    snapraid -p 5 -o 20 scrub

Automation

Since SnapRAID requires manual commands, it is highly recommended to automate these tasks using scripts. The SnapRAID AIO Script is a popular community solution for automating syncs, scrubs, and monitoring.

Recovery

Undeleting Files

If a file is accidentally deleted, SnapRAID can restore it to its previous state (like a backup).

Restore specific file:

snapraid fix -f /path/to/file

Restore specific directory:

snapraid fix -f /path/to/directory/

Restore only missing files: Use the -m flag to recover deleted files without overwriting existing changed files.

snapraid fix -m -f /path/to/directory/

Recovering a Failed Drive

In the event of a total disk failure, follow this procedure strictly.

1. Halt Operations Disable any automated tasks (cron jobs, AIO scripts) and stop writing new data to the array.

2. Reconfigure Install the replacement disk and mount it. Edit /etc/snapraid.conf to point the failed disk identifier to the new mount point.

  • Example: Change data d1 /mnt/failed_disk to data d1 /mnt/new_disk.

3. Fix (Restore Data) Run the fix command targeting the specific disk identifier (-d). Log the output to a file on a different drive for review.

snapraid -d d1 -l fix.log fix
  • Note: This process will read from all other disks to reconstruct the missing data. It runs at the speed of the slowest drive.

4. Review Check fix.log for "unrecoverable" errors. If files were modified since the last sync, they may not be fully recoverable.

5. Verification (Optional) Run a check on the restored disk to verify integrity.

snapraid -d d1 -a check

6. Resync Once verified, run a standard sync to update the array status.

snapraid sync