![]() ![]() In fact, the AFS server can even reboot the AFSclient on your workstation simply waits till AFS comes back to life. But when MITNet gets its act back togeether,the AFS client in your workstation seems to have no trouble carrying onfrom where it was. MITNet partitions occasionally, and yourworkstation loses contact. Athena uses the Andrew File System (AFS), which also useswhole-file caching.Remote users who dial in with 300-bit/second modems may findthis annoying.) The server may send a 300 Mbyte fileacross the net when the client intends only to read and change a 10-bytechunk. Disadvantage: large files soak up bandwidth and cachespace, perhaps unnecessarily. Also, simplicity of failure modes:discovery that a file is not available locally, and thus must beretrieved-or won't be available, because we are running in disconnectedmode-can occur only at open time, never when reading or writing a pieceof the file. Advantages? Disadvantages? (Advantages: a sweepingsimplification, especially of the user's mental model of what isavailable when disconnected.What if there is a weird crash or the network goes down in themiddle of writing a modified file back? Doesn't that mean that someoneelse may read a partially modified file? (On write-back, Coda creates ashadow file only after all the data has made it across the network doesthe server do an exchange of the shadow file with the original.Similarly, when a modified file iswritten back to the server, the whole file is transmitted.) And theclient cache holds the whole file. The paper refers to "whole-file caching"? What is that? (When aclient reads a file from the server, the server insists on sending thewhole file, not just the part the client was interested in. ![]() For example, howconcerned should the server get if a client doesn't acknowledge acallback? The client may have crashed, or it may just be temporarilydisconnected.) Keeping that state consistent with theactual state of the client is hard, because clients should be assumed tobe undependable-they may forget their own state.
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