The main objective of this paper is to find the optimal guest file system for hypervisor-based virtualization with the Oracle’s VirtualBox virtual machines. For this research, we decided to measure file system performances, in equal conditions and apply the same test method. For testing purposes, we used Filebench software, which guarantees equality and independence of the hardware and operating system characteristics. CentOS 7.9 with the latest updates is used as the guest operating system, while VirtualBox 6.1 is used as the hypervisor. Performances are compared for the cases of one and two virtual machines running simultaneously. Expected behaviors are analyzed with Filebench, while the results are used to verify the assumption.