SQL* (1/24/2013)
High availability : Means 99.99% of times data must be available.
By who's definition? 4 nines is too much for some, not enough for others. Your uptime requirements for HA are defined by the business, not an arbitrary set of numbers.
For this if we take an example, if the Primary db goes down then the secondary will become as primary in each and every options (Clutering/Miroring/Logshipping),
Not necessarily. A single database failure may well not force the cluster to fail over as clustering is designed to protect the instance and the server. If a database becomes unavailable because the disk array it was on has failed, clustering will be of no help there because the databases are on shared storage (unless you're doing a cluster without shared storage, which is hard)
If someone drops a critical table, neither clustering nor mirroring will help there. Log shipping however might allow for the table to be retrieved.
what is the point to mention two technical words HA/DR for the same thing.
They're not the same thing.
High availability - remaining available and online no matter what
Disaster recovery - getting back online after some disaster
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability