SnapRAID is a backup program for disk arrays.

• It stores parity information of the data and it recovers from up to six disk failures.
• It is mainly targeted for a home media center, with a lot of big files that rarely change.

sudo apt install snapraid

df -h

returns:

Filesystem                        Size  Used Avail Use% Mounted on
/dev/nvme0n1p2              ext4      1.8T  1.7T   14G 100% /
...
/dev/sdb                    ext4       15T   14T  286G  98% /mnt/disk1
/dev/sdc                    ext4       15T   13T  1.5T  90% /mmt/disk2
/dev/sdd                    ext4       15T   14T   30G 100% /mnt/disk3
/dev/sde                    ext4       15T   14T  3.2G 100% /mnt/disk4
/dev/sdf                    ext4       15T   14T   56G 100% /mnt/parity1
/dev/sdg                    ext4       15T   14T  233G  99% /mnt/parity2
mergerfs                           34T   24T   10T  69% /mnt/media

Edit the main configuration file for SnapRAID, /etc/snapraid.conf.

A basic configuration for three data disks and one parity disk looks like this:

/etc/snapraid.conf

# Parity files - stored on the largest disks or dedicated parity drives.
1-parity /mnt/parity1/snapraid.parity
2-parity /mnt/parity2/snapraid.parity
 
# Content files - store metadata; should be on multiple drives for redundancy.
content /var/snapraid.content
content /mnt/disk1/.snapraid.content
content /mnt/disk2/.snapraid.content
content /mnt/disk3/.snapraid.content
content /mnt/disk4/.snapraid.content
 
# Data drives - these contain actual files.
data d1 /mnt/disk1
data d1 /mnt/disk2
data d2 /mnt/disk3
data d3 /mnt/disk4
 
# Excludes hidden files and directories
exclude *.unrecoverable
exclude /tmp/
exclude /lost+found/
exclude downloads/
exclude appdata/
exclude *.!sync