[Gluster-users] Configuration suggestions (aka poor/slow performance on new hardware)

Ed W lists at wildgooses.com
Thu Apr 1 13:22:25 UTC 2010

>     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


Ed W

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