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Replicated Volumes

In a Coda file system a Volume is a logical grouping of files which is typically smaller than a partition and larger than a single directory. Volumes can be non-replicated, replicated read-only or replicated read-write. It is the latter two that are of particular interest to us.

Each replicated volume has a Volume Server Group or VSG which all contains all the servers that carry the volume. The Available Volume Server Group or AVSG contains the servers in the VSG that are currently accessible. When a client wants to retrieve an object from a volume, information about the object is retrieved from all servers in the AVSG. If this information is inconsistent then resolution procedures are invoked. This mechanism is beyond the scope of this paper. Once that client has the object information it works on a read from one, write to many basis. The cost of the write to many semantic is minimised by the use of broadcast RPC calls.



Horms
1999-03-07