File system virtual appliances: Portable file system implementations

File system virtual appliances (FSVAs) address the portability headaches that plague �file system (FS) developers. By packaging their FS implementation in a VM, separate from the VM that runs user applications, they can avoid the need to port the fi�le system to each OS and OS version. A small FS-agnostic proxy, maintained by the core OS developers, connects the FSVA to whatever OS the user chooses. This paper describes an FSVA design that maintains FS semantics for unmodi�ed FS implementations and provides desired OS and virtualization features, such as a uni�fied buffer cache and VM migration. Evaluation of prototype FSVA implementations in Linux and NetBSD, using Xen as the VMM, demonstrates that the FSVA architecture is efficient, FS-agnostic, and able to insulate fi�le system implementations from OS differences that would otherwise require explicit porting