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Hi Mike, re: > After doing some testing I think I have discovered the answer to my question > but wanted to run it by you guys and make sure this is a correct conclusion. > > When configuring the LDM's ldmd.conf file for multiple sources for primary > and alternate feeds, such as the example listed on the Unidatas' web site. > > REQUEST ANY ".*" host1.site1.edu # initially primary-mode > REQUEST ANY ".*" host2.site2.edu # initially alternate-mode > > > My assumption was that the LDM compared only the MD5 checksums from the > alternate site against the data flowing in from the primary and any product > that primary did not get sent from the primary site would be sent from the > alternate feed site. Also, I had assumed that the data sent to/from the > alternate site, was low bandwidth data, MD5 checksum data only. The following comments pertain to LDM 6.4+ distributions: When the regular expressions in the replicated feed requests are identical, then the slower feed process will fall back to being an alternate while the faster stays as a primary. The decision for this partitioning is made semi-continuously so when the two upstream sites are able to feed the downstream equally fast, the connections will likely change from alternate to primary and back (because over the time period in which the decision is made, it is likely that products come from one site). When an upstream is feeding in alternate mode, it offers products to the downstream one-by-one. If the downstream has not already received the product being offered, it will accept it. If the number of products accepted in one feed exceeds the number of products accepted by another feed, the downstream (receiver) will force a disconnection from the upstream and request a new feed that operates as a primary. If the number of products received by the downstream by a primary upstream feeder is less than another feed, then the connection will be broken and a new, alternate feed request will be sent to the upstream. Please remember that this assumes that the set of possible products being sent from each upstream is identical. > My testing of bandwidth usage with Cacti SNMP graphs and iptraf, indicates > that when you include an alternate site in the ldmd.conf file, you are > *doubling* the incoming data volume, since both sites are sending the entire > requested data sets, not just the MD5 comparison data from alternate site. This should not be the case _unless_ the regular expressions for the data being requested are identical. For instance, if your example requests were: REQUEST ANY ".*" host1.site1.edu # initially primary-mode REQUEST ANY "(.*)" host2.site2.edu # initially alternate-mode the two requests would be different, and each feed would be established as a primary. > So my question is...Is it true by adding a alternate feed site you effective > get two sets of the same data stream, ie double the bandwidth consumption? It will be true if the regular expressions for the requested data products are different. If they are not, you should not see double the number of products being sent. > If this is true, I may not be the only LDM user that unaware of this and > implications of bandwidth usage. I believe that the LDM documentation describes how replicated feed requests work. > Thanks for your help and clarification on this issue. No worries. Cheers, Tom **************************************************************************** Unidata User Support UCAR Unidata Program (303) 497-8642 P.O. Box 3000 address@hidden Boulder, CO 80307 ---------------------------------------------------------------------------- Unidata HomePage http://www.unidata.ucar.edu **************************************************************************** Ticket Details =================== Ticket ID: TWA-232236 Department: Support LDM Priority: Normal Status: Closed