Data Domain SNMP server may fail to return queries to client


   Article Number:     519084                                   Article Version: 4     Article Type:    Break Fix 




Data Domain





SNMP (Simple Network Management Protocol) is based on the stateless UDP protocol. It is an extremely simple and fast way for a SNMP client to query a SNMP server for information (and depending on configuration, to also set changes remotely), by identifying the item of data to be queried or set by a known OID (Object ID). Note the DD SNMP agent only supports read queries, but not setting of information.   
    On a regular host the SNMP daemon replies to incoming requests, the replies are typically fast as the queries tend to be for items the underlying operating system provides quickly: process and load information, network traffic details, etc. The Data Domain gives this generic information, but also gives more Data Domain-specific data, and some of these are collected through "sms" jobs from the SNMP agent when the query is received. Some of these queries may be for data that takes extra time to be collected.   
    The end result is, depending on the configured timeout on the SNMP client, some queries to the DD may appear to have been lost or not replied to at all, when it was simply the DD taking a longer time to respond. The DD SNMP agent is single-threaded, so it will only service one SNMP query at a time. If a query takes a longer time to be processed, all queries received afterwards may be either dropped or replies made after the client side timeout has expired, resulting in further errors.   






The DD SNMP daemon is single threaded and there are no plans to make it parallel so that several queries may be serviced at the same time.   
    There is a functional need for some queries to trigger "sms" jobs for collecting the data, some of these jobs while running normally, may take more time to complete than the response timeout period of the SNMP client. Depending on the client there may be some tuning available to extend this timeout to a longer value.   
    If your SNMP client or backup application sees repeated errors collecting SNMP data from a DataDomain, please open a support request with your contracted support provider, gather all the possible details, a Support Upload Bundle, and refer to this KB article when providing the details.