File System Virtual Appliances: Third-party File System Implementations without the Pain (CMU-PDL-08-106)

File system virtual appliances (FSVAs) address a major headache faced by third-party FS developers: OS version compatibility. By packaging their FS implementation in a VM, separate from the VM that runs user applications, they can avoid the need to provide an FS port for every kernel version and OS distribution. A small FS-agnostic proxy, maintained by the core OS developers, connects the FSVA to whatever kernel version the user chooses. Evaluation of prototype FSVA support in Linux, using Xen as the VM platform, demonstrates that this separation can be efficient and maintain desired OS and virtualization features. Using three existing file systems and a cooperative caching extension as a case study, we demonstrate that the FSVA architecture can insulate FS implementations from user OS differences that would otherwise require explicit porting changes.