From: Muench, Joanna (jmuench_at_fhcrc.org)
Date: Mon Feb 23 2004 - 16:08:28 PST
The paper by Howard et al. (1988) on a distributed file system presented an
interesting discussion of the design and implementation of a scalable
system. The paper suffered somewhat from a lack of clear motivation and odd
organization (two different prototypes). It did, however, re-iterate several
concepts that we have come across in readings on RPC and virtual memory
management over a distributed network and provided a useful comparison with
the Unix NFS.
The basic concept of Andrew is a set of servers (called Vice) that stores
the shared files. Each server has a list of all the shared files with either
the address of the server owning that file or the file itself. After a
client has requested a file, the server will notify that client before
allowing a modification by another workstation. One of the key concepts
discussed in the paper included a whole-file transfer approach. This
significantly reduces the number of calls required between the client and
server, but does present a problem for files larger than the local disk
cache.
I didn't quite understand one of the consistency semantics, that "Multiple
workstations can perform the same operation on a file concurrently." This
sounds wonderful except for the final sentence, "Application programs have
to cooperate in performing the necessary synchronization if they care about
the serialization of these operations". But doesn't that require special
application development and really break the concept of transparency?
Because the system was built using an RPC package had many of the issues we
have already discussed such as name resolution, transparency, the
client-server relationship and authentication. Unfortunately the
authentication issue was mentioned only in passing.
The paper demonstrates that Andrew outperforms the Unix NFS due to a number
of factors including lack of robustness of the NFS RPC protocol under load.
The comparison didn't seem entirely reasonable, given the different goals of
NFS vs. Andrew.
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