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My Permanent Address: Finding a File after it has Moved

Muntz, Dan; Liu, Lisa


Keyword(s): file systems; migration; distributed

Abstract: The DiFFS file service, an ongoing project at HP Labs, supports migration of file system objects (files and directories) at the granularity of individual objects. The original design to support object migration relies on forwarding pointers stored at the object's previous location to determine the object's new location. There are various difficulties with implementing this scheme, and thus other mechanisms are being considered. One approach to solving this problem is to consider how similar situations are handled in other contexts. When students go off to college, they fill out many forms over the subsequent years asking for their home address. This permanent address can be used to communicate with the student during these years when the student is likely to change locations several times. A new mechanism for locating migrated objects is based on this model-objects are assigned permanent addresses. When an object cannot be found at its expected location, i.e., the object has migrated, a message can be sent to the object's permanent address to retrieve its current location. This permanent address model decouples the forwarding information from the site of the object's previous location, providing greater flexibility for this functionality. It also solves a problem with the proposed method of dealing with volatile file handles in the NFSv4 specification.

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