Unrar Archives Split Across Different Filesystems

The unrar utility can extract files from a multi-volume archive split across different filesystems, but it does not scan multiple storage paths automatically. By default, unrar expects all archive parts to reside within the same directory. However, you can successfully unpack split archives spanning separate drives, partitions, or network mounts by using interactive path prompting, symbolic links, or filesystem virtualization.

Method 1: Interactive Path Prompting

The native command-line version of unrar includes built-in support for spanning multiple volumes across different locations:

Run the extraction command on the primary or first volume:
```
unrar x /path/to/filesystem1/archive.part1.rar
```
When unrar finishes processing the first volume and cannot locate the next part in the same directory, the extraction pauses and prints a prompt:
```
Cannot find volume archive.part2.rar
Enter the path to this volume or press Enter to cancel:
```
Type the full path to the next file on the other filesystem (for example, /mnt/drive2/archive.part2.rar) and press Enter.
Repeat this step for each subsequent volume located on different filesystems.

Note: This approach only works in interactive terminal sessions. If you use automated scripts with the -y (assume yes) flag, the extraction will abort when a volume is missing.

Method 2: Symbolic Links (Recommended for Automation)

If you need a non-interactive, automated workflow, you can assemble the split parts into a single logical directory using symbolic links (symlinks) without copying large files.

Create a temporary folder on any accessible filesystem:
```
mkdir /tmp/rar_merge
```

Create symlinks pointing to the archive pieces across your different filesystems:

ln -s /mnt/storage_a/backup.part01.rar /tmp/rar_merge/backup.part01.rar
ln -s /mnt/storage_b/backup.part02.rar /tmp/rar_merge/backup.part02.rar
ln -s /mnt/storage_c/backup.part03.rar /tmp/rar_merge/backup.part03.rar

Extract the archive directly from the temporary folder:

unrar x /tmp/rar_merge/backup.part01.rar /destination/path/

Because unrar follows standard filesystem symlinks, it will read each part sequentially from its respective physical drive while perceiving them as a unified set in a single directory.

Method 3: Union Mounts

For complex storage setups where you regularly deal with archives distributed across multiple physical disks or network shares, you can combine the storage locations using a union filesystem such as MergerFS or UnionFS:

mergerfs -o defaults,allow_other /mnt/disk1:/mnt/disk2 /mnt/unified

Once mounted, /mnt/unified presents the files from both disks under a single virtual directory, allowing unrar to automatically detect and extract every volume without manual intervention.