This article describes about the possibility of expanding disk size of VSRX deployed in KVM.

Expanding disk size in VSRX is not possible. Disk size is fixed for VSRX 2.0 and VSRX 3.0.

vSRX 2.0 is 16GB

VSRX 3.0 is 18GB

Refer the document for more details: https://www.juniper.net/documentation/us/en/software/vsrx/vsrx-consolidated-deployment-guide/vsrx-kvm/topics/concept/security-vsrx-system-requirement-with-kvm.html