SnapRAID & MergerFS Storage Setup

Problem

Managing a collection of mismatched hard drives as a single pool while maintaining data redundancy (parity) without the overhead or risk of a traditional RAID 5/6 array.

Solution

A combination of MergerFS for pooling and SnapRAID for parity. This is ideal for "mostly static" media storage (like MajorRAID) where files aren't changing every second.

1. Concepts

MergerFS: A FUSE-based union filesystem. It takes multiple drives/folders and presents them as a single mount point. It does NOT provide redundancy.
SnapRAID: A backup/parity tool for disk arrays. It creates parity information on a dedicated drive. It is NOT real-time (you must run snapraid sync).

2. Implementation Strategy

Clean the Pool: Use rmlint to clear duplicates and reclaim space.
Identify the Parity Drive: Choose your largest drive (or one equal to the largest data drive) to hold the parity information. In my setup, /mnt/usb (sdc) was cleared of 4TB of duplicates to be repurposed for this.
Configure MergerFS: Pool the data drives (e.g., /mnt/disk1, /mnt/disk2) into /storage.
Configure SnapRAID: Point SnapRAID to the data drives and the parity drive.

3. MergerFS Config (/etc/fstab)

# Example MergerFS pool
/mnt/disk*:/mnt/usb-data /storage fuse.mergerfs defaults,allow_other,cache.files=off,use_ino,category.create=mfs,minfreespace=20G,fsname=mergerfsPool 0 0

4. SnapRAID Config (/etc/snapraid.conf)

# Parity file location
parity /mnt/parity/snapraid.parity

# Data drives
content /var/snapraid/snapraid.content
content /mnt/disk1/.snapraid.content
content /mnt/disk2/.snapraid.content

data d1 /mnt/disk1/
data d2 /mnt/disk2/

# Exclusions
exclude /lost+found/
exclude /tmp/
exclude .DS_Store

Maintenance

SnapRAID Sync

Run this daily (via cron) or after adding large amounts of data:

snapraid sync

SnapRAID Scrub

Run this weekly to check for bitrot:

snapraid scrub

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