Prism: Lightweight Filesystem Virtualization Via Selective Cloning
نویسندگان
چکیده
Suppose filesystems supported cloning of any subset of directories, even those containing gigabytes of data, almost instantaneously, while guaranteeing isolation between the original copy and the cloned copy. We show that this simple abstraction can greatly simplify many routine tasks, both for a single operating system and for clusters of similar virtual machines in a virtual server farm. In this paper, we describe the design of Prism, a file server that supports lightweight cloning and centralized file management of multiple filesystems. Unlike copying in standard file systems or cloning operations on virtual disks, the Prism filesystem supports high-level operations to create fast clones of any part of a filesystem. After cloning, each cloned file system can evolve independently, providing similar read/write semantics as if the file systems were copied from each other. This abstraction is useful for supporting virtual server farms. It is possible to create filesystems for new virtual machines interactively, while protecting private home directories, log files, and password files. Furthermore, when cloned systems have a high degree of similarity, Prism makes centralized scanning operations (e.g., for malware checking) for multiple cloned file systems significantly faster than scanning each file system individually. Prism’s capabilities are also applicable to individual operating systems. Prism can help provide lightweight file system isolation between processes to prevent untrusted code from damaging the filesystem. Prism is currently implemented by extending the ext3 filesystem. On the Postmark benchmark and the Apache build workload, Prism’s performance is comparable to that of a standard ext3 filesystem. For applications that require scanning or comparing multiple, cloned filesystems, Prism is significantly faster. This paper describes the design and evaluation of the Prism filesystem.
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