Keith Freedman wrote: > the issue isn't reliability, it's availability. > > if a client only talks to one server and that server goes down then the > client has nothing to 'fail over' to. however, if the client talks to > both servers then if one goes down it'll keep talking to the other one. Either the clients will honour the RRDNS and pick another server, or they won't - unfortunately, we now have a case where two opposing possibilities are being presented. To wit : From the ? Gotcha ? page : http://www.gluster.org/docs/index.php/AFR_(Automatic_File_Replication)_-_Things_to_keep_in_mind_and_gotchas Applies to server side [...] "The clients connect only to 1 server. You would need to implement some kind of load balancing or something either with round robin DNS [...]" "If you have client1 connected to server1 and client2 connected to server2, and then server2 goes down, so does client2. The cluster also becomes unavailable." Ok, that seems like a straightforward enough statement, however, if we take a look back through the mailing list archives, we find a statment from Mr. Anand Avati which suggests exactly the opposite : http://lists.nongnu.org/archive/html/gluster-devel/2008-04/msg00007.html [...] "Or, put another way, if ClientA (by chance) resolves roundrobin.gluster.local to 192.168.252.1, but .1 is currently down - what happens ? it will attempt on .2, and if that fails (or disconnects after a while), it will attempt on .3, and once all the entries are used 'once', it will do a fresh dns query. it does not honor dns refresh timeouts (yet)." The remaining basic question then is this : does AFR w/ RRDNS failover work or not ? If it does, then the ? Gotcha ? page should be updated, /and/ further investigation is required to determine why it failed to operate as advertised in my environment. If it does /not/, then the ? Gotcha ? page should be updated, and the wiki page i wrote (based largely on the suggestions of the developers) should likely be scrapped. :P As always, thank you all for your continued discourse ! -- Daniel Maher <dma+gluster AT witbe DOT net>
