Rsync Dual Disk Backup Guide

Rsync Dual Disk Backup Guide | Generated by AI

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Question: Suppose I have two disks to back up some files totaling 50 GB. How do I use rsync to sync between my computer and two portable disks?

Answer:

For a simple backup strategy with two portable disks (e.g. two external USB drives), the most common and reliable approach is:

Treat your computer (source folder) as the single source of truth.
Use rsync to mirror that source to each portable disk separately (one rsync run per disk).
This gives you two independent, identical backups.

Rsync does not natively copy to multiple destinations in one command (unless using advanced batch mode or scripts), so you run it twice — once for each disk.

Recommended rsync command (macOS / Linux)

Connect both portable disks. Assume:

Your files to back up are in: ~/ImportantData/ (or /path/to/your/50GB/folder/)
Disk 1 mounts as: /Volumes/BackupDisk1
Disk 2 mounts as: /Volumes/BackupDisk2

Use this safe & commonly recommended set of options:

# First backup — to Disk 1
rsync -avh --progress --delete \
  --exclude='.*' \
  --exclude='Desktop' --exclude='Downloads' --exclude='Library' \
  ~/ImportantData/  "/Volumes/BackupDisk1/ImportantData Backup/"

# Then to Disk 2 (same command, just change destination)
rsync -avh --progress --delete \
  --exclude='.*' \
  --exclude='Desktop' --exclude='Downloads' --exclude='Library' \
  ~/ImportantData/  "/Volumes/BackupDisk2/ImportantData Backup/"

Key options explained:

-a = archive mode (recursive + preserves permissions, times, symlinks, etc.)
-v = verbose (shows what’s happening)
-h = human-readable sizes (easier to read)
--progress = shows transfer progress for each file (very useful for 50 GB)
--delete = deletes files on the backup disk that no longer exist in source (true mirror/backup)
--exclude='.*' = skips macOS hidden files (.DS_Store, ._* files, etc.) — very common on macOS to avoid junk
Add more --exclude for folders you never want to back up (e.g. caches, temp files)

First time vs. later times

First run (empty destination): Will copy all ~50 GB → takes longest (hours depending on USB speed).
Later runs (incremental): Only changed/new/deleted files are processed → usually very fast (seconds to minutes).

Even better / safer variants

Add –dry-run first (simulation — highly recommended!):

rsync -avh --dry-run --progress --delete ~/ImportantData/ "/Volumes/BackupDisk1/ImportantData Backup/"

Run this → check output → make sure nothing unexpected gets deleted.

Keep modification times & extended attributes (good on macOS):

rsync -aEvh --progress --delete ...
# -E preserves macOS extended attributes / resource forks

Log the backup (very useful for later checking):

rsync -avh --progress --delete --log-file=~/backup-log-$(date +%Y-%m-%d).txt \
  ~/ImportantData/ "/Volumes/BackupDisk1/ImportantData Backup/"

Make it fully automatic (one script):

Create a file backup.sh:

#!/bin/bash

SOURCE="$HOME/ImportantData/"
DEST1="/Volumes/BackupDisk1/ImportantData Backup/"
DEST2="/Volumes/BackupDisk2/ImportantData Backup/"

echo "Backing up to Disk 1..."
rsync -avh --progress --delete --exclude='.*' "$SOURCE" "$DEST1"

echo "Backing up to Disk 2..."
rsync -avh --progress --delete --exclude='.*' "$SOURCE" "$DEST2"

echo "Backup finished at $(date)"

Then run: bash backup.sh

Tips for 50 GB on portable disks

Use USB 3.0+ ports and drives → much faster than USB 2.0.
First backup: do it overnight or when you don’t need the computer.
Eject disks properly after backup (diskutil eject /Volumes/BackupDisk1).
If disks are used only for backup → format them as APFS (macOS) or exFAT (cross-platform).
Alternative tools if you want rotation/history (not just mirror): rsync + --backup --backup-dir=../backups/$(date +%Y-%m-%d) or tools like rsnapshot/Borg.

This gives you two separate, up-to-date backups — rotate them (e.g. keep one offsite) for better protection.

References:

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