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ACtive-ACtive Clustering SQL server 2005 Expand / Collapse
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Posted Monday, October 11, 2010 1:38 AM
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Hi if any one knows ACtive-ACtive Clustering SQL server 2005 disadvantages.

Please help me out.
Post #1001961
Posted Monday, October 11, 2010 1:49 AM


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Read this.

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Post #1001967
Posted Monday, October 11, 2010 4:32 AM


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Essentially if you have two servers and want to leverage the most out of them you would use an active/active (if one fails the instance fails over to the second node and vice versa). Obviously this is good when everything is fine cause you get two servers, double the grunt and can share databases between the two.

Essentially what you will have are two active/pasive clusters (that fail to each other).

The situation gets better if you can have a third node which can be a shared passive notde for the two active nodes. BUT and heres the disadvantages: If you have a shared passive for both active nodes, what happens if they both failover to the passive? Can it handle the load? Remember to be part of a Windows cluster the hardware must be identicle, so following failover your active instances will be sharing 1 node so will have less the 50% of the resources they had.

We are in a fortunate position where investment for infrastructure has never been an issue. We have two active/passive clusters (2 seperate nodes per cluster) and a thrid node (per cluster) at SCF for database mirror failover.

Back to your questions: As i see it the disavantages with a/a are that it is not a high availability solutiion r ather a high performance solution. What happens in the case of a failure? What is acceptable to the business? Only you or your boss can answer these questions.

For my money, i'd rather have half the grunt but now i am protected! A/P all the way.

Hope this helps.


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Post #1002039
Posted Tuesday, October 12, 2010 5:53 AM


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Microsoft pushes Clustering as the next best thing to sliced bread. In my experience we have had more downtime with clusters than with a regular server. Clusters are very touchy and the smallest things can make them fail over. 100% CPU usage for a certain length of time can cause them to fail over... We have two active/passive clusters here and three active/active clusters here. Installing SQL 2008 in a clustered environment is a royal pain. I had so many problems just getting it installed I had to call support.


Post #1002704
Posted Tuesday, October 12, 2010 6:08 AM


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Markus (10/12/2010)
Microsoft pushes Clustering as the next best thing to sliced bread. In my experience we have had more downtime with clusters than with a regular server. Clusters are very touchy and the smallest things can make them fail over. 100% CPU usage for a certain length of time can cause them to fail over... We have two active/passive clusters here and three active/active clusters here. Installing SQL 2008 in a clustered environment is a royal pain. I had so many problems just getting it installed I had to call support.


Sorry to hear that. I'm afraid to say that your clusters have obviously not been configured or tuned correctly. Ours are bomb-proof!


Adam Zacks

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Post #1002718
Posted Tuesday, October 12, 2010 6:50 AM
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I have to second the previous comment. We've been running clusters (Sql Server and Oracle) for years and the only time these clusters fail over is when we manually fail them over for patches. They have been solid.

For a few of our clusters, I run Active/Active and as said previously, you have to account for the scenario where both instances are running on the same node. Essentially you want to be sure to spec the servers properly. For example, we set max server memory for each instance to about 45% of the total memory.

Side Note:
There was a post here some time ago where someone dynamically configured the memory on failover/startup so they could use up to 90% of the memory when the sql instances were running on their separate nodes.



Post #1002755
Posted Tuesday, October 12, 2010 7:07 AM


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In response to Markus's comment - we have many clusters, ranging from 2-node A/A clusters to a 6-node N+1 (N Active / 1 Passive) cluster for our SQL instances, and they all work very well, and are stable, the biggest issues we have are hardware related, not clustering. And, if your machines are running at very high CPU loads, your servers are probably underpowered, or you have runaway processes.

In response to Schadenfreude-Mei's comments (1) to be part of a Windows cluster the hardware must be identicle, No, the hardware doesnt have to identical across the cluster, it just has to be certified (for Win 2003 or earlier), or pass validation for Win 2008. (2) disavantages with a/a are that it is not a high availability solutiion r ather a high performance solution A/A clusters are still High-Availability, just with a extra risk that the remaining node may not be able to handle the load without degraded performance; to be a High-Performance solution, it would require a Load-Balancing cluster, not a Failover cluster.

The biggest issue you should watch for is if all nodes except 1 failed, could the remaining node handle all the instances. Benchmark the load (CPU / memory / IO), if you can, to get a good indication of the resulting load.



Post #1002771
Posted Tuesday, October 12, 2010 8:20 AM


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A/A clusters are a good way to maximize hardware investment. One thing I advise my clients is to have a monitoring agent of some flavor trigger on a failover and automatically adjust the sql server max memory on BOTH systems to an appropriate value that totals to the amount an indivitual machine should take on the given hardware. This will avoid memory contention problems. I also advise being cautious with Lock Pages in Memory setting on these servers for same reason.

Best,

Kevin G. Boles
SQL Server Consultant
SQL MVP 2007-2012
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Post #1002863
Posted Tuesday, October 12, 2010 9:42 AM


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Markus (10/12/2010)
Microsoft pushes Clustering as the next best thing to sliced bread. In my experience we have had more downtime with clusters than with a regular server. Clusters are very touchy and the smallest things can make them fail over. 100% CPU usage for a certain length of time can cause them to fail over... We have two active/passive clusters here and three active/active clusters here.


I work with 3 different clusters at present and they all perform without issue, have you verified your cluster configurations?


Markus (10/12/2010)
Installing SQL 2008 in a clustered environment is a royal pain. I had so many problems just getting it installed I had to call support.


it's fine if you slipstream the SP1 during install time or create a merged drop installer


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Post #1002949
Posted Tuesday, October 12, 2010 9:19 PM
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TheSQLGuru (10/12/2010)
A/A clusters are a good way to maximize hardware investment. One thing I advise my clients is to have a monitoring agent of some flavor trigger on a failover and automatically adjust the sql server max memory on BOTH systems to an appropriate value that totals to the amount an indivitual machine should take on the given hardware. This will avoid memory contention problems. I also advise being cautious with Lock Pages in Memory setting on these servers for same reason.


Kevin, what type of monitoring agents are these that will automatically adjust the sql server max memory?
Post #1003337
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