March 13, 2008 at 8:12 am
Is there any good reason to have both Clustering AND one of the following? (Log shipping or DB Mirroring)?
¤ §unshine ¤
March 13, 2008 at 8:37 am
More redunant? Money burning? I never see a company have them at the same time.
March 13, 2008 at 8:39 am
I can think of two main reasons for log shipping:
1. Disaster Recovery - you can hold a copy of your database on a different site with log shipping.
I think with clustering the nodes have to be in close proximity.
2. Reporting – By log shipping your db to another any reports run against can be run against the log shipped version of the database which will not impact on performacne of the transactional system>
Gethyn Elliswww.gethynellis.com
March 13, 2008 at 9:10 am
Clustering provides high-availability and DR for hardware failure, but not site failure.
Mirroring or Log Shipping provides DR for hardware failure and site failure, but depending upon how you set up mirroring/log shipping you can not always confirm both prod and failover are in sync.
Cluster failover can occur within seconds and is automatic whereas mirroring/log shipping is not as simple to fail over to. Client connectivity is impacted since you can not have 2 SQL instances on the same domain with the same server\instance name. It's time consuming in a recovery situation to have to repoint apps to a new SQL instance.
Reporting, as previously suggested is another reason for mirroring/log shipping a clustered db.
- Tim Ford, SQL Server MVPhttp://www.sqlcruise.comhttp://www.thesqlagentman.com http://www.linkedin.com/in/timothyford
March 13, 2008 at 9:19 am
Timothy Ford (3/13/2008)
Cluster failover can occur within seconds and is automatic whereas mirroring/log shipping is not as simple to fail over to. Client connectivity is impacted since you can not have 2 SQL instances on the same domain with the same server\instance name. It's time consuming in a recovery situation to have to repoint apps to a new SQL instance.
If your app is using SQL Native connections, there's apparently some switch you can put on the conn strings to automatically redirect if the principal in a mirror is "dead". Meaning - it will automatically start talking to the backup if the principal is detected down.
Still not as efficient as cluster failover, but not quite as bad as manually repointing to a new location
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Your lack of planning does not constitute an emergency on my part...unless you're my manager...or a director and above...or a really loud-spoken end-user..All right - what was my emergency again?
March 13, 2008 at 9:42 am
So if we have a cluster and want a DR recovery site, which would be better, Mirroring or Log Shiping. I know mirroring may be easier to set up but log shipping is better for performance??? is this correct?
¤ §unshine ¤
March 13, 2008 at 9:59 am
For the DR site, I'd go with log shipping. If you use HA mirriorring (automatic fail over), and you have a node failure in your cluster, the mirrior will fail over to the DR site faster than the passive node in the cluster fails over. Pretty sure that isn't what you'd want to occur.
Also, if you are log shipping, and you have a predetermined delay between backup and restore, you could catch data integrity issues before they hit your DR site, such as a development manager dropping a table from production because he thought he was on the development system.
(Not me, but someone I worked for, and not in a SQL environment but an COBOL/ISAM environemnt).
😎
March 13, 2008 at 11:48 am
Thank you so much all!
¤ §unshine ¤
March 13, 2008 at 12:03 pm
Clustering is a high availability solution, not a disaster recovery solution. Clustering provides high availability because it automatically swings all the data to another server, in the event of failure. Clustering does not provide redundant data because only one node has has the data. If a natural disaster strikes and completely obliterates all of your servers, you have no redundant data to fall back on. If you data is important to you and the company, you NEED something more to fall back on. Mirroring and log shipping give you the ability to off load data to remote servers. Mirroring is free and provides nearly instantaneous transfer of data.
To answer the question, the reason companies like to have both is because they like the security of knowing that in the event of a catastrophic disaster, they can still get their business up and running.
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