I wanted to share my experience because I was seeing unusually high CPU usage on my XOA VM during backup operations.

Environment:

• XCP-ng pool with multiple hosts
• XOA running as a VM
• SSD RAID10 NFS storage
• Daily delta backups (~17 production VMs)
• Weekly backup jobs with Health Checks
• Backup window previously around 7 hours

Symptoms before optimization:

• XOA CPU usage frequently close to 100%
• During backups, multiple backupWorker.mjs processes saturated available CPUs
• XOA felt sluggish while backups were running
• Backup jobs took significantly longer than expected
• htop showed worker processes fighting for CPU resources

Original XOA VM configuration:

• 2 vCPU
• 4 GB RAM
• 1 socket / 2 cores

Observed htop behavior during backups:

/usr/local/lib/node_modules/xo-server/node_modules/@xen-orchestra/backups/backupWorker.mjs

Several workers continuously consumed nearly all available CPU.

IMPORTANT:

Run the following commands via SSH directly on the XCP-ng Pool Master.

Do NOT perform these changes through the Xen Orchestra GUI itself because you are modifying the XOA VM that is currently managing your environment. Otherwise you may lock yourself out or interrupt your own management session during the reconfiguration process.

Connect to the Pool Master:

ssh root@<POOL-MASTER-IP>

First identify the XOA VM UUID:

xe vm-list | grep -i xoa -B1 -A2
or:
xe vm-list name-label="<YOUR-XOA-VM-NAME>"

Example output:

uuid ( RO): xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
name-label ( RW): XOA-Production
power-state ( RO): running

Copy the UUID for the following steps.

Test procedure:
I increased XOA resources to:

New XOA configuration:

• 4 vCPU
• 8 GB RAM
• CPU topology: 1 socket / 4 cores

Procedure used:

1. Shutdown XOA VM

xe vm-shutdown uuid=<XOA-VM-UUID>

Wait a few seconds and verify status:

xe vm-list
uuid=<XOA-VM-UUID>
params=name-label,power-state

2. Set memory

xe vm-memory-limits-set
uuid=<XOA-VM-UUID>
static-min=8GiB
dynamic-min=8GiB
dynamic-max=8GiB
static-max=8GiB

3. Increase vCPU count

xe vm-param-set
uuid=<XOA-VM-UUID>
VCPUs-max=4

xe vm-param-set
uuid=<XOA-VM-UUID>
VCPUs-at-startup=4

4. Set CPU topology

xe vm-param-set
uuid=<XOA-VM-UUID>
platform:cores-per-socket=4

5. Start XOA again

xe vm-start uuid=<XOA-VM-UUID>

Verification:

xe vm-param-get
uuid=<XOA-VM-UUID>
param-name=VCPUs-max

xe vm-param-get
uuid=<XOA-VM-UUID>
param-name=VCPUs-at-startup

xe vm-param-get
uuid=<XOA-VM-UUID>
param-name=platform

xe vm-list
uuid=<XOA-VM-UUID>
params=name-label,power-state

Results from the same backup job:

Before:

• Backup size: 10.58 GiB
• Transfer speed: 150.21 MiB/s
• Total duration: 3 minutes
• Health check transfer: 2 minutes

After:

• Backup size: 10.71 GiB
• Transfer speed: 229.12 MiB/s
• Total duration: 2 minutes
• Health check transfer: 1 minute

Measured improvement:

Transfer throughput:
+52%

Backup duration:
-33%

Health check transfer:
-50%

After the upgrade, htop showed backup workers distributed across all available CPUs instead of saturating only two cores.

Conclusion:

For my environment the bottleneck was not:

• NFS
• Storage
• SSD RAID10
• Host performance

The bottleneck appears to have been XOA itself being underprovisioned.

If you are running larger backup jobs, health checks, multiple workers, or backup-heavy environments, increasing XOA resources may provide a noticeable improvement.

I still need to test the full nightly production run (~17 VMs), but initial results are very promising.

Hope this helps someone.