> My understnding is that both mirroring and caching are various means of
> replication,
> but some people, notably the I2-DSI, tend to understand that replication
> is more
> a synonym of mirroring with caching being something other. There was no
> problem
> until we spok of caching and mirroring, but then came 'replication' ...
The point of view of the I2-DSI project is that caching and mirroring are
both *mechanisms* which implement *service replication*. Service replication
simply means having equivalent services available at more than one location.
Mirroring works by copying the server source files while caching works
by replicating the server's output. Mirroring is not tied to a static policy,
and caching is not tied to a dynamic policy - these are specific choices.
There are other service replication mechanisms which are neither mirroring
nor caching.
Admitted there is a confusion in terminology because mirroring uses
*file replication* as a mechanism to implement *service replication*.
Service replication is a higher-level concept than mirroring and caching,
and correctness is relative to the specification of the service.
For example, some services might require bit-for-bit identical responses from
the replicas whereas others might only require that they fit the same
general description.
I2-DSI admits both mirroring and caching as examples of service replication,
but since there is so much mature work in caching the project is focusing
on generalizations of file mirroring. We seek to eventually integrate
caches as a service replication mechanism for use when appropriate.
If WREC wants to talk about caching and mirroring as instances of something,
then I suggest that "service replication" is a good candidate.
Micah Beck Research Associate Professor
mbeck@cs.utk.edu Innovative Computing Laboratory
Department of Computer Science
(423) 974 - 3548 University of Tennessee
- 8296 (FAX) Knoxville, TN 37996-1301
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