Question: heloo yahoocan i know what is called clustering in hardware? 

Answer: Pretend you have 10 servers. You want them all to be mail servers, because you are running a DC (Data Center) and you have 10 branches, different parts of the country.  \n\nNow, you want data load balancing, so that not all of one server is taking the brunt of things. You also want to keep administration at a minimum.  So you cluster.\n\nNow that we have a situation, here's what happens.  You maintain load balance by having 10 servers, that are looked at as one. Say you have a cluster of ten and the naming convention is ms01,ms02,ms03, etc. until you get to 10 (ms10).  The cluster can be named clmail01.\n\nThis is great, because you are keeping load balance at a minumum, but what about the admin part.  \n\nWell, let's say you want to give Dallas and Houston (2 of the 10 branches) to use mail server ms04 and ms05, well then so be it, but whether it is Dallas, Houston, or Denver (another one of the 10 branches), they all see it as as clmail01. In real application, it would have to be an FQDN (Fully Qualified Domain Name), so Dallas, Houston, and/or Denver would all see it as clmail01.domain.tld\n\nAnother big thing not mentioned is security.  This is HUGE, and by setting up clusters, you have increased security.  By setting up a cluster, you are more/less using a frontend/backend environment. This means that if clmail01 is attached and hacked into, the main mail servers (ms01-ms10) are not touched.\n\nPonder about this :)\n\nHave fun, and hope this has helped.
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