April 27, 2011 at 12:19 am
Hello,
I'm doing research on setting up a cluster (Win2008/SQL Server 2008 EE). We have 2 instances that, for reasons of replication, must be in the same resource group. I will have 3 blades for the cluster. I haven't yet tested how well both SQL Server 2008 instances run on one node. At the moment, I'm thinking of either a 2-node active/active cluster or a 3-node active/passive cluster with one passive node, once I figure out wher to put the shared storage.
And it is the shared storage that I am not sure about. Will I need to dedicate one of the blades as the shared storage or do I have the possibility of using the disk-array on the passive node as shared storage? From what I have read online, it seems that I cannot
Aside from the issue of single-points-of-failure, if it is possible, is this a really bad idea: having 2 elements of a cluster on one machine?
I would appreciate the experience of others, please.
Many thanks
April 27, 2011 at 10:20 am
In Cluster environment if 1 node failed then services move on another node but logically you can install second instance of sql server on the same cluster but you have to define separate shared disk for this instance and MSSQL binaries(installation files),common files installed on the drive where windows install or C:\ we can say
Regards,
Syed Jahanzaib Bin Hassan
MCTS | MCITP | OCA | OCP | OCE | SCJP | IBMCDBA
My Blog
Regards,
Syed Jahanzaib Bin Hassan
BSCS | MCTS | MCITP | OCA | OCP | OCE | SCJP | IBMCDBA
My Blog
www.aureus-salah.com
April 27, 2011 at 10:47 am
Do you not have a storage array, i.e. SAN? Normally, you'd have 2 (or more) servers connected to a dedicated storage device. The local disks on the servers would only be used for the OS and binaries. The SQL Data files, log files, quroum, MSDTC, etc. would be on the SAN. You could run the Cluster Validation Wizard, which will tell you whether your configuration is cluster capable.
April 27, 2011 at 12:08 pm
Sean,
The install will not let you install two instances in the same cluster group, as far as I know it is not a supported configuration. You *might* be able to jerry rig it in but I wouldn't. I was going to do something similar a while back, 4 instances, 2 cluster groups (1 group with 1 and one group with 3 instances). While you might be able to install an unclustered SQL box on those drives getting them to be clustered is not a good plan.
Each instance will require its own cluster group, disk, IP, server name, AND instance name. It won't let you do ServerName\Instance1 and ServerName\Instance2. You have to have completely different names.
I'd like to understand why replication is defining this configuration.
CEWII
April 28, 2011 at 12:44 am
@Syed Jahanzaib Bin hassan: I understand the logic of services being started on the chosen node on failover. I'm not clear about the definition of the shared disks. They must surely be on another physical server (or, more likely, a SAN, as adb has pointed out). Since I will have 3 blades to work with, I was wondering if it were possible to have 2 elements of the cluster on one physical machine, namely the passive node and the shared storage. In a worst (working) case scenario it would mean a No Majority: Disk Only quorum configuration.
@adb2303: You are correct, we have a storage array. I have to check if it may be used.
@Elliott Whitlow: That's good to know. You asked about the replication. We are a quasi-government organisation and we manage a public DB as well as our own private ones. Data from one is required in the other and it was decided that this data would be transmitted from instance A to instance B by means of replication. However, it becomes somewhat complicated because the application of instance B can also write and amend data in the replicated tables on instance A. As a consequence, the application requires that both instances A and B be up. Testing how cluster-aware the application is and how well it handles failover is a pending task for our developers.
Thank you all for your help. I have to clarify the SAN-usage with our sysadmins
April 28, 2011 at 6:01 am
The replication only requires both instances to be up, they don't have to be in the same resource group.
A resource group is just a bunch of applications and resources moving together, you can have one instance up on one machine and the other on another and the replication will keep running fine.
They don't even have to be on the same cluster (they don't even have to be clustered at all).
If you have a 3 node cluster, install both instances on all 3 nodes, start the first instance on node A, the second instance on node B and set both preferred fail-over node to C, that way you would need to have 2 nodes down to end up with both instances on the same machine.
April 28, 2011 at 6:14 am
Hi Oliii
We are running two instances joined by replication at the moment. I have been told that I will be getting 3 blades for the cluster. One node must be able to run both instances at peak capacity at an acceptable performance. We must have two active nodes, one per SQL Server instance. That is two of the blades spoken for.
Depending on how the stress tests go, a two-node active/active cluster may be acceptable. I am just looking at possible topologies at the moment.
My query concerns the shared storage, the possibility of a passive node and whether it is possible and not foolhardy to have the shared storage and the passive node on the third blade. All of the indications are that I can't. I also have to hear back from our SAs about the using the SAN for the shared storage.
Many thanks for your reply.
Sean.
April 28, 2011 at 6:28 am
I guess we are not talking about the same kind of shared storage 🙂
Why do you need shared storage?
When you assign a SAN LUN to a resource group its only available on the current node and invisible on the other, if you need both instances to access the same share it's better to setup a file share accessible from any nodes.
You could also mount a LUN on each node (each with the same letter) but not set it up as a cluster resource and ask your SAN dude to make it available on all 3 blades.
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