
96 High Performance Parallel I/O
Any requests that modify back-end file system data or metadata must be
made idempotent to ensure that retry attempts due to lost RPC replies are
harmless and that clients receive the correct replies. Clients therefore include a
unique XID in each request to allow repeated requests to be identified and the
server retains a copy of the RPC reply buffer until it has positive confirmation
that the reply was received by the client.
The server also includes both the OSD transaction number in which the re-
quest was executed and the OSD’s last committed transaction number in RPC
replies. Clients retain the RPC request and reply ...