Virtual Scanner Appliance Sizing

This section provides guidance on sizing the Virtual Scanner Appliance to ensure optimal performance and stability based on your scanning needs.

Default Configuration

The Qualys Virtual Scanner Appliance is provisioned with the following default configuration, which is sufficient for most use cases. For larger deployments - such as scanning large web applications or a large number of targets (hundreds or more) - you may need to scale CPU, memory (RAM), and disk resources as described below.

Resource	Default Value
vCPU	4
Memory (RAM)	8 GB
Disk Space	56 GB

In version 3.10, restrictions are lifted, allowing you to configure more than 16 vCPUs and 16 GB of RAM. 

Recommended vCPU: RAM Ratio

The default vCPU-to-RAM ratio is sufficient for some cases. You can increase the number of vCPUs and memory resources to enhance your scanning capacity. However, it is essential to maintain a vCPU-to-memory ratio of either 1:3 or 1:2, depending on your platform's flexibility for scaling adjustments.

Qualys recommends a maximum of 64 GB of RAM, proportionally matched with the vCPU at a 1:3 or 1:2 ratio. For example, if you set the scanner to use 64 GB of RAM, you should configure it to have either 20 or 32 vCPUs.

However, if your virtual scanner needs to handle a large number of scan targets, increasing the RAM size boosts scanning capacity (though not speed). It helps prevent the scanner from becoming overloaded.

The following table shows the outcomes for the recommended and not recommended vCPU: RAM ratio:

vCPU: RAM Ratio	Recommendation	Outcome
1:3	Optimal	Ideal balance for performance and stability
1:2	Acceptable	Works based on platform flexibility
>1:3	Suboptimal	May cause vCPU bottlenecks and underutilized memory
<1:2	Not recommended	Risk of memory overcommitment; may cause scan failures

Work directly with your Technical Account Manager or Qualys Support for help with scanner capacity and sizing calculations based on your scanning needs. 

Increase Virtual Disk Size

Increasing the disk size is necessary only if you frequently run out of disk space during scans. This is more likely when scanning large web applications, scanning hundreds or more targets, or running scans with debug logging enabled.

Recommended Disk Size

• Standard scan workloads: approximately 56 GB (default disk size)

• Scanning large web applications, hundreds or more targets, or running scans frequently: at least 100 GB

The default disk size (~56 GB) is sufficient for typical scan workloads. For large environments, high target counts, or frequent scanning, Qualys recommends provisioning at least 100 GB of disk space.

If disk space becomes exhausted during scans, increase the allocated virtual disk size. In addition, ensure that the Debug Scan field is disabled in the Qualys Enterprise TruRisk™ Platform before scheduling scans, as debug logging can significantly increase disk consumption and may impact scanner performance or availability.

To increase the virtual disk size, perform the following steps: 

1. Stop the scanner instance.

2. Find the Hard Disk/Storage field in your scanner VM instance settings and increase the disk size.

3. Save your settings and start up your scanner.

Your scanner instance should generate the new disk size. It also automatically resizes all partitions and file systems.

Change vCPU and RAM Size  

You can increase or decrease vCPU and RAM.  

The maximum supported size for a scanner instance is 64 GB RAM with a vCPU: RAM ratio of 1:3 or 1:2. Allocating more memory than this will be wasted. 

As mentioned earlier, the number of vCPUs must be proportional to the allocated RAM and disk space. Use a ratio of 1:2 or 1:3 for vCPU: RAM. For example, 4 vCPUs with 12GB RAM or 8 vCPUs with 16 GB of RAM.  

To change the vCPU/RAM allocated for a scanner instance, perform the following steps: 

1. Stop the scanner instance.

2. Find the vCPU/RAM options in your scanner VM instance settings and choose the desired size.  

3. Save your settings and start up your scanner.