[Gluster-users] Possible to use gluster w/ email services + Tuning for fast replication

Ed W lists at wildgooses.com
Mon Nov 1 20:29:57 UTC 2010

> Right now, I am testing out a 2 node setup, with one server replicating data to another node. One thing I noticed was when I created a file or directory on the server, the new data does not replicate to the other node. The only time data is synced from server to the other node is when I run "gluster volume rebalance test start". Is this normal? I had envisioned gluster would constantly replicate changes from the server to the other nodes, am I off base?

Are you examining the second node directly, ie not by mounting it?  I 
think the point is that replication only happens when you "observe" the 
second node?

Glusterfs is targeted for HTPC applications where typically the nodes 
are all connected over high performance interlinks.  It appears that 
performance degrades very quickly as the latency between nodes increases 
and so whether the solution works for you is largely going to be 
determined by the latency between nodes on your network connection.

I'm not actually sure what some representative numbers should be?  I 
have two machines hooked up using bonded-rr intel gigabit cards 
(crossover to each other) and these ping at around 0.3ms.  However, I 
have one other machine on a gigabit connection, hooked up to a switch 
and that sometimes drops to around 0.15ms...  I believe infiniband will 
drop that latency to some few tens of microseconds?

So basically every file access on my system would suffer a 0.3ms access 
latency.  This is better than a spining disk with no cache which comes 
in more like 3-10ms, but obviously it's still not brilliant

Please let us know how you get on?

Good luck

Ed W

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