What happens to your files when the single NAS sitting in your closet fails? If the answer is “I hope nothing bad happens,” that’s a problem worth fixing today. A NAS backup to another NAS is one of the most reliable ways to protect data without paying monthly cloud fees. It keeps a full copy on hardware you control, and it can run on a schedule without anyone touching it.
The idea sounds simple: copy everything from one box to another. In practice, plenty of people set this up wrong. They mirror deletions, leave the backup on the same network as the original, or never test a restore. This guide covers the methods that work, the mistakes that quietly ruin backups, and how to build a setup that survives a real disaster.
Why a second NAS beats a single drive or a cloud subscription
A single external drive is cheap, but it is also fragile and easy to forget. A second NAS gives you a dedicated machine that runs on its own schedule, holds far more data, and can sit in another room or another building. It also gives you versioning options that a plain USB drive cannot match.
Cloud storage remains a solid third layer, but it has two drawbacks for large libraries: recurring cost and slow restores. Pulling several terabytes back down from the internet can take days. A local NAS-to-NAS copy restores at network speed, which on a wired gigabit link is roughly 100 to 110 megabytes per second in real-world conditions. (Network-attached storage)
The classic 3-2-1 rule still frames the conversation: three copies of your data, on two different types of media, with one copy offsite. Two NAS units handle the first two parts neatly. The offsite piece is where planning matters, whether that means a unit at a relative’s house or a cloud tier for the most critical files. Photographers and videographers who keep large raw libraries often pair this approach with dedicated photo backup solutions so that irreplaceable images get their own protection layer.
The four main ways to copy one NAS to another
There is no single “right” method. The best choice depends on the brands involved, the filesystems, and how much control you want.
| Method | Best for | Speed | Main trade-off |
|---|---|---|---|
| rsync over SSH | Mixed brands, Linux-based units | Fast after first sync | Manual setup, command-line comfort helps |
| Snapshot replication (ZFS or Btrfs send/receive) | Matching filesystems on both ends | Very fast, block level | Both units must support the same filesystem |
| Vendor tools (same brand only) | Synology to Synology, QNAP to QNAP | Fast, guided setup | Locks you into one ecosystem |
| SMB or NFS mount plus a copy job | Beginners, small datasets | Slower | Weak error handling, no built-in versioning |
rsync: the dependable cross-brand workhorse
rsync is the most portable option. It works between almost any two Linux-based NAS units, transfers only changed blocks, and can preserve permissions and timestamps. The official rsync project documents every flag in detail. The key decision is whether you want a mirror or a versioned archive.
A mirror with `–delete` makes the destination an exact copy of the source. That is efficient, but dangerous: if ransomware encrypts the source, the next run happily encrypts the backup too. A safer pattern keeps deleted and changed files in a dated folder on the destination, so you can roll back. Running with `–dry-run` first is a habit worth keeping, because it shows exactly what would change before anything moves.
Snapshot replication: fast, but picky about hardware
If both units run ZFS or Btrfs, snapshot replication is the strongest option. Instead of comparing files one by one, the system sends only the blocks that changed since the last snapshot. That makes it dramatically faster on large datasets and gives you point-in-time copies that cannot be silently altered. The catch is compatibility: both ends need the same filesystem and a working send/receive path, which usually means building or buying units with that in mind.
Vendor replication tools: convenient, same-brand only
Synology, QNAP, and TrueNAS all ship replication features. Synology offers Snapshot Replication and Hyper Backup, with a companion service on the target unit. QNAP uses Hybrid Backup Sync and its RTRR protocol. TrueNAS has built-in replication tasks. These tools are genuinely good, and they handle scheduling, encryption, and retention without a terminal. The limitation is obvious: they generally work best when both units come from the same vendor. Feature names and menus shift between software versions, so check the current documentation for your specific model before relying on a setting.
Setting up your first NAS-to-NAS backup: a workable sequence
A repeatable order of operations prevents most surprises. This sequence works for nearly any method above.
- Give the backup NAS a fixed address. Use a static IP or a DHCP reservation so jobs never fail because the target moved.
- Create a dedicated backup account. Do not reuse an admin login. Grant access only to the folders being copied.
- Connect over a wired link if possible. Wi-Fi adds latency and drops connections during long initial syncs.
- Run the first full copy during off-hours. The initial transfer is the bottleneck; everything after it is incremental.
- Schedule recurring jobs for a quiet window, typically overnight.
- Set retention. Keep daily versions for a week, weekly for a month, and monthly for a year, or whatever fits your storage.
- Turn on notifications. An alert about a failed job is the whole point of automation.
- Test a restore. Pick a random folder, restore it to a scratch location, and open the files.
That last step is the one people skip. A backup that has never been restored is a hypothesis, not a safeguard. Practically speaking, restoring a handful of files monthly catches permission problems, missing folders, and silent job failures long before a real emergency.
Common mistakes that quietly break backups
Most failed backup stories trace back to a handful of avoidable errors.
Mirroring deletions without versioning. The backup faithfully copies the damage. Versioned snapshots or dated folders are the fix.
Keeping both units on the same network with the same credentials. If an attacker compromises one, the other is one hop away. Separate accounts, restricted permissions, and immutable snapshots reduce the blast radius. Keeping the backup unit powered off between runs, or placing it at another location, adds a physical barrier.
Never checking capacity. A backup job that runs out of space may fail silently or stop partway. Set a storage alert at 80 percent full.
Ignoring the initial sync time. Copying 10 terabytes over gigabit takes well over a day, sometimes several. Plan for it and avoid restarting the job halfway.
Forgetting encryption in transit and at rest. Sensitive files deserve encrypted transfers, especially if the backup unit lives somewhere else.
Skipping the restore test. Covered above, and worth repeating because it is the most common gap.
How this fits into a wider backup strategy
A NAS-to-NAS copy is one layer, not the whole plan. The strongest setups stack layers: fast local copies for quick recovery, offline or offsite copies for disaster protection, and cloud tiers for the most critical documents. If the goal is resilience against power problems as well as disk failure, pairing a backup NAS with reliable backup power is sensible. Options like the best home generators or solar generators for home backup power keep both units running through outages and prevent the unclean shutdowns that can corrupt filesystems.
Physical media still has a role too. Periodically copying the most important data to a drive that lives in a drawer or a safe gives you an air-gapped copy that no network attacker can reach. A shortlist of the best external hard drives for backup covers that layer well. The pattern to remember: local NAS copy for speed, offsite or offline copy for survival, cloud for convenience.
Performance and scheduling in the real world
Expect the first sync to dominate everything. After that, incremental runs move only changed data, so a nightly job on a typical home library finishes in minutes. A few practical notes help:
- Wired beats wireless. A stable gigabit link is worth the cable run.
- Throttle if needed. Most tools support bandwidth limits so backups do not saturate the network during work hours.
- Stagger jobs. Do not run the backup at the same time as other heavy tasks on either unit.
- Watch the logs. A job that “completes” in seconds when it usually takes an hour deserves a look.
- Keep firmware current. Replication features get security fixes; outdated software is a common weak point.
For anyone building a broader home data strategy, the same principles behind choosing the best home generators apply here: redundancy matters more than any single component, and the cheapest failure is the one you planned for. (NIST Cybersecurity Framework)
Conclusion
Backing up one NAS to another is one of the highest-value projects in home and small-office data protection. It removes the single point of failure, restores at local speed, and costs far less over time than cloud storage for large libraries. The method matters less than the discipline: pick rsync, snapshot replication, or a vendor tool based on your hardware, then set a schedule, keep versioned copies, separate the credentials, and test a restore on a regular basis. Do those things and a failed drive becomes an inconvenience instead of a catastrophe.
Frequently asked questions
Can I back up a Synology NAS to a QNAP NAS?
Yes. Cross-brand copies work well with rsync over SSH, which both platforms support, or by mounting one unit’s shared folder on the other over SMB or NFS and running a scheduled copy job. Vendor-specific tools like Hyper Backup or Hybrid Backup Sync are most reliable when both units share a brand, so for mixed hardware the generic protocols are the safer route.
How long does the first NAS-to-NAS backup take?
It depends almost entirely on data volume and link speed. On a wired gigabit connection, expect roughly 100 megabytes per second under good conditions, so a 4 terabyte library takes around 11 to 12 hours at best. Many small files, slower drives, or Wi-Fi will stretch that considerably. Later incremental runs are far quicker because only changed data moves.
Is NAS-to-NAS backup enough on its own?
Not quite. Two units in the same building protect against drive failure, but not fire, flood, theft, or a network attacker who reaches both machines. The 3-2-1 rule recommends one copy offsite. Adding an offsite unit, a rotated external drive kept elsewhere, or a cloud tier for critical files closes that gap.
What is the difference between mirroring and versioned backup?
A mirror makes the destination identical to the source, including deletions. A versioned backup keeps older copies, so a deleted or corrupted file can be recovered from an earlier point in time. Versioning costs more storage but protects against ransomware, accidental deletion, and sync errors. For most people, versioned snapshots are worth the extra space.
Will a NAS backup protect me from ransomware?
Only if it is set up correctly. A live mirror with saved credentials can be encrypted along with the source. Protection comes from immutable or offline snapshots, separate backup accounts with limited permissions, and keeping at least one copy unreachable from the main network. Test that you can restore from a snapshot before you need it.
Do I need identical NAS units for snapshot replication?
No, but both ends must support the same filesystem for block-level replication to work. ZFS send and receive requires ZFS on both sides, and Btrfs snapshots require Btrfs. Units from different vendors can still replicate if they share that filesystem support. Otherwise, fall back to rsync, which works across nearly any combination of hardware.
