DC & DR

Once you are able to understand and imagine a datacenter, I want to Introduce another term called DC the full form of which is "Datacenter" but there is a slight difference in this Datacenter and the previous Datacenter which we read about in the previous section, I know I am confusing you now, let me explain

DC is the term used by the IT world referring to a “Primary datacenter” and yes there is something called as “Secondary datacenter” as well which we denote as DR the full form of which is "Disaster Recovery"

We ideally host our production Infrastructure; the servers, storage, software out of a primary site known as datacenter (DC)“a physical location”, all the banks customers / users connect to this datacenter to access the production applications

Now imagine if this datacenter site goes down or some kind of disaster happens at this site then all our applications would be inaccessible and would result in a major loss to our business, ideally in simple words “we can’t afford such kind of downtime”, so to deal with such scenarios we build a Disaster Recovery site which hosts the exact replica of the datacenter applications so that if the DC site goes down then all the users / customers can connect to the applications from DR and the business keeps running

To reiterate DC and DR are 2 separate Datacenters placed in separate locations, at least more than 100 Km’s (different Siesmic regions) apart where DC acts as a Primary Datacenter where all your applications are Live, reachable and connectable from the users and DR is a Secondary Datacenter which hosts a Replica or a Copy of all the applications of the DC and it acts as a failover site or a cold site such that if some calamity happens in the DC or the entire DC goes down then the DR would become primary and start hosting the applications and serving the users, in this way you can avoid any downtime "Service not available" of your applications

If you are thinking how can we have an exact copy of applications and data 100 Kms away then please clear your mind and internalize the fact that it’s very much possible and there are technologies which can have your data copied continuously to the Secondary site "100 Km’s away" in almost realtime and this is exactly how all Enterprises host their applications and Data

So, next time if you here someone saying "My DC is located in Mumbai and DR in Chennai" you must be able to figure out that the Primary datacenter for this company is hosted in Mumbai and the secondary datacenter is in Chennai

In the IT world, you should be aware of the interchangeable use of many “Words” such as DC equal datacenter but only the Primary one, the Secondary Datacenter would never be called as DC although it is also a datacenter it would always be called out by the Acronym DR (Disaster Recovery)

Another term with regards to DR or planning DR is BCP (Business Continuity Planning), planning a DR so that your Business can run continuously without any interruptions even in case of a Disaster in the Primary Site, that’s BCP

One more important point to note is that the DC and DR sites are connected via a WAN link, WAN link is nothing but a network connectivity between the 2 sites, generally this connectivity is provided to you by the ISPs "Internet Service Provider", telecoms such as Tata and Reliance provide these WAN links

Diagram Depicting a DC and a DR and the Internet based user connectivity to both DC and DR

Side Note: Don’t be overwhelmed by the complexity of these diagrams if you feel so, if you keep on reading ahead you may be able to comprehend all these concepts easily