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Next: 2.3 Reliability Issues Up: 2 The Design of Previous: 2.1 Server and Client

2.2 Device Operation

All server workstations run an NRD server process, which stores a number of disk blocks and handles all block read and write requests. The NRD client accepts read or write as a normal disk, and when it wants to read or write a number of blocks, it searches its block table to find out on which server the corresponding blocks reside, and starts sending requests to that server.

In case of native memory-demanding processes starting on a server workstation, part of the server's virtual memory is swapped to disk. Future requests will be serviced from the disk, thus degrading performance. The problem can be handled by the server which can send a message to the client notifying of its memory-loaded state. The latter will try to find another server having enough free memory and migrate the disk blocks that were stored on the loaded server to a new one. If this is not possible, the delay of requests to the loaded server are inevitable.

Mike Flouris
Thu Sep 17 18:12:15 EET DST 1998