3) ACK sent once X server machines have received the request (to
ram). Data loss possible if all server machines lost before they
write the request to disk. Good compromise of speed vs reliability
guarantees
This functionality can be achieved by loading write-behind translator
on server-side (on top of posix translator).
Nearly, but not quite. Remember we can ACK before all servers have
received the request. In the case of variable latency to different
servers (and assuming you are IOPs bound) then this potentially buys you
increased IOs/sec:
In the simplest situation of a single server then we have roughly
achieved the effect of moving the writeback cache to the
serverside. In the case of multiple servers with exactly equal
latency to the client then we have roughly achieved the same as
moving writeback cache to serverside on all servers. In the case
of non equal latency between client and server, or with server
side replication, or with very busy servers then we gain a
performance improvement due to the lower latency before the ACK
sent to the client
Cheers
Ed W
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