Backing Up VMware ESXi VMs to Synology NAS with Active Backup for Business: A 3-2-1 Data Protection Strategy – ITFROMZERO

Context: When Snapshots Are Not a Backup

After nearly six months managing a VMware ESXi infrastructure for a mid-sized business, I learned an expensive lesson — literally. Snapshots let you roll back quickly after configuration changes, but they still live on the same datastore. When the RAID controller failed, both the snapshots and the VMs vanished before we could react.

The minimum standard in enterprise environments is the 3-2-1 strategy: 3 copies of your data, stored on 2 different media types, with 1 copy off-site. Synology NAS with Active Backup for Business (ABB) is a combo many sysadmins choose because the software is completely free — you only invest in the NAS hardware once.

I previously migrated a personal lab from VMware to Proxmox and found Proxmox’s built-in backup quite convenient. But in an enterprise environment with ESXi already running in production, swapping hypervisors isn’t always feasible. ABB integrates directly with the VMware API and uses CBT (Changed Block Tracking) to copy only the changed blocks — incremental backups after the initial full run take minutes instead of hours.

System Requirements

Synology NAS: DS923+, DS1522+, or an equivalent model that supports ABB (check the compatibility list)
DSM: version 7.0 or later
VMware ESXi: 6.5, 6.7, 7.0, or 8.0
ESXi and NAS must be on the same LAN or reachable via IP (a dedicated VLAN for backup traffic is recommended)
An ESXi account with All privileges, or at minimum Virtual machine → Configuration → Change Settings and vStorage API for Data Protection

Installing Active Backup for Business on Synology

Step 1: Install the Package from Package Center

Log into DSM, go to Package Center → search for Active Backup for Business → install. ABB is free, but you need to activate the license via your Synology Account — also free, just takes a few minutes to register.

The first time you open ABB, it redirects you to the Synology Account login page for activation. Once that’s done, you’re ready to go.

Step 2: Create a Shared Folder for Backups

Go to Control Panel → Shared Folder → Create and create a folder named vm-backup. Make sure to enable Data Checksum — without it, silent data corruption won’t be detected until you need to restore, which is too late. If your NAS has multiple volumes, place this folder on the largest one.

Configuring the VMware ESXi Connection

Create a Dedicated Backup User on ESXi

Using root for backups is bad practice. Create a dedicated user with only the necessary permissions — SSH into ESXi or use vSphere Client:

# SSH into the ESXi host
esxcli system account add -i backup-user -p 'StrongPass@2024' -c 'StrongPass@2024'
esxcli system permission set -i backup-user -r Admin

If you’re using vSphere/vCenter instead of a standalone ESXi, create the user in vCenter and assign the Virtual Machine Power User role combined with vStorage API permissions.

Enable Changed Block Tracking (CBT) on VMs

CBT allows the backup tool to copy only the blocks that have changed, skipping everything else. For a 500 GB VM writing 15–20 GB per day, an incremental backup completes in 10–15 minutes instead of hours. ABB enables CBT automatically when you add a VM to a backup job, but the VM must either be powered off or have VMware Tools running.

Add the ESXi Host to ABB

Open Active Backup for Business → go to the VMware tab → click Add VMware vSphere:

Server: IP address or hostname of the ESXi host (e.g., 192.168.10.10)
Port: 443 (default)
Username: backup-user
Password: the password you created

Click Test Connection — a successful connection displays host information and a list of VMs. On first connection, ESXi’s SSL certificate is usually self-signed; ABB will ask whether you want to trust it — click Trust.

Creating a Backup Task and Configuring Details

Create a New Backup Job

After adding the ESXi host, go to Backup Task → Create:

Task name: use something meaningful, e.g., ESXi-Production-Daily
Backup source: select the VMs to back up — you can pick individual VMs or the entire host
Destination: select the vm-backup shared folder you created
Backup mode: choose Incremental (after the initial full backup, only changed blocks are backed up)

Configuring the Backup Schedule

The schedule I use for small-to-medium production environments:

Full backup: Sunday at 2:00 AM
Incremental backup: Monday through Saturday at 3:00 AM

In the ABB interface, go to Schedule → Custom and configure it to your needs. Choose off-peak hours — CBT-based backups are fairly lightweight but still add noticeable I/O if run during peak hours.

Configuring Retention Policy

Many people skip this section, then panic a few months later when the NAS is full. Basic configuration:

Keep all versions for: 7 days (retain all restore points for one week)
Keep daily versions for: 30 days
Keep weekly versions for: 3 months

ABB uses deduplication — identical blocks across restore points are stored only once. In practice, with 5 VMs totaling 2 TB of disk, I used around 800 GB on the NAS after 3 months. Not bad at all.

Advanced Option: Quiescing VMs During Backup

Enable application-aware backup if a VM is running SQL Server, Exchange, or another database. This feature calls VSS (Volume Shadow Copy Service) to flush transactions to disk before taking the snapshot — preventing backups of a database in an incomplete state that won’t start after restore.

Requirement: VMware Tools must be installed and running on the VM guest.

Testing and Monitoring

Running the First Backup

After creating the task, click Back Up Now to run the initial full backup. The first run will take a while depending on data size — 1 TB typically takes 2–4 hours depending on storage and network speed. Monitor progress in the Log tab:

# Check logs on the NAS via SSH (for debugging)
cat /var/log/synology/activebackup/activebackup.log | grep -i "error\|warn" | tail -50

Verifying Backups with a Test Restore

A backup you’ve never tested is not really a backup. ABB supports Instant Restore — boot a VM directly from the NAS without copying files back to ESXi first. How to test:

Go to Restore → VMware
Select the VM and the restore point you want to test
Choose Instant Restore to VMware
The VM boots from the NAS — verify that data and services are intact
Once confirmed, shut down the instant-restore VM — don’t run production workloads directly from NAS

I make it a habit to test a restore once a month, picking 1–2 VMs at random. It sounds like extra work, but it’s the only way to know for certain that your backup doesn’t just run — it actually restores when you need it.

Configuring Email Alerts

Go to DSM Control Panel → Notification → Email and set up SMTP. Then in ABB, go to Settings → Notification and enable alerts for backup failures. Also enable the Health Report for a weekly summary — it saves you from having to check the dashboard every day.

Daily Dashboard Monitoring

ABB’s overview dashboard covers the basics. Four metrics to check daily:

Last backup status: must show Successful, not Warning or Failed
Protected/Unprotected VMs: make sure no VM is accidentally left out
Storage usage: track growth rate to plan disk purchases before you run out
Transfer speed: a sudden drop often signals a network issue or high NAS load

Completing the 3-2-1 Strategy

Backing up VMs from ESXi to NAS via ABB covers 2 of the 3 requirements: the original on ESXi and the backup copy on the NAS — 2 copies, 2 media types. What’s still missing is the off-site copy.

Synology offers Hyper Backup to sync data to the cloud or to another NAS at a different location. For VM backups, syncing the vm-backup folder to Backblaze B2 on a weekly schedule is a practical choice — roughly $3/month for 500 GB, much cheaper than Amazon S3 (~$12/month for the same capacity).

The ESXi + Synology ABB + Hyper Backup to cloud stack gives you a complete data protection system without Veeam or Zerto costing thousands in licensing. The NAS hardware is a one-time cost, the software is free, and your data stays in your hands.