possessed by portable devices, while simultaneously preserving the consistency, robustness and ease of shar- ing/collaboration provided by distributed file systems.

One can envision many extensions to lookaside caching. For example, the client cache manager could track portable device state and update stale files auto- matically. This would require a binding between the name space on the device and the name space of the dis- tributed file system. With this change, a portable device effectively becomes an extension of the client’s cache. Another extension would be to support lookaside on in- dividual blocks of a file rather than a whole-file basis. While this is conceptually more general, it is not clear how useful it would be in practice because parts of files would be missing if the portable device were to be used directly rather than via lookaside.

Overall, we believe that the current design of looka- side caching represents a sweet spot in the space of de- sign tradeoffs. It is conceptually simple, easy to im- plement, and tolerant of human error. It provides good performance and availability benefits without compro- mising the strengths of portable storage devices or dis- tributed file systems. A user no longer has to choose be- tween distributed and portable storage. You can cache as well as carry!

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