SQL* (1/24/2013)
Hi,Thanks,
But can you tell me any scenarios where we can use Clustering/Mirroring together.
I'll keep this brief as there are already a wealth of articles and white papers on this subject and I do have a day job 😉
A typical use of clustering and mirroring would be to provide mitigation in the following scenario
Live site
has a 2 node cluster serving the SQL Server instance that has the database "ImportantFinancialData". The 2 node cluster's only purpose is to provide high availablility in that, if the active node suffered a CPU failure, there is a spare node to continue serving the database to clients.
DR Site
On the DR site there is a sql server instance that is a mirror partner to the Primary database "ImportantFinancialData" on the Live site. The only purpose of this DR server is to serve a copy of the database if the cluster is lost on the Live site.
SQL* (1/24/2013)
Actually I am very much confused on High availability/Disaster Recovery options.
It would help if you understand a little about each of the technologies about what they do and how they achieve it, you would then be able to see how they can bolt together as a single entity.
Clustering purely provides hardware mitigation at the server\instance level. If the active node fails the whole clustered sql server instance fails over not just individual databases.
Database mirroring provides failover capability at the database level. If a mirrored database fails over it does not fail all databases on the instance of SQL Server. The mirror database is in a state that does not allow users to query the database unless you are using the approrpiate edition of sql server and have snapshots configured.
SQL* (1/24/2013)
High availability : Means 99.99% of times data must be available.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), we are achieving this Manually/Automatically. Why the Primary goes down, may be because of H/W failures or scheduled maintenance right... then we can say this as Disaster Recovery.... what is the point to mention two technical words HA/DR for the same thing.
The availability depends on your SLA, it just numbers but some organisations actually factor in 5% downtime for example as a maintenance window.
HA and DR are essentially 2 different things. Providing HA just means that my 2 cluster nodes on my Live site ensure that the database server is always available even when i want to apply patches.
DR can mean so much but is essentially a means of providing service when the Live site has disappeared down a black hole in the planets surface.
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