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andre.wibisono
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Active-Active Controllers

Hi...

We are currently doing a POC for Compellent SC8000. We are using two SC8000. We noticed that there is only one active controller.

Is there anyway to make the two controllers active to always load balance the workload?

We checked with our local dell representative who is assisting us with the POC, he told us that that's how compellent works. It won't load balance.

The second controller will be active only during:

- failure of primary controller.

- the primary can no longer take the workload (which may not happen in our POC because the load is not that huge - considering the maximum load a single controller can take).

Thanks.

Regards,

Andre

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3 Replies
Moderator
Moderator

Re: Active-Active Controllers

Both of the controllers are active however, the controllers do not automatically move volumes to the other controller for IO purposes but for example when you create the 1st volume it will get assigned to controller A. When you create a second volume it then gets assigned to Controller B. Now if Volume 1 is high IO and you create a 3rd Volume it will also be assigned to Controller A and it also is high IO then you will have both high IO volumes on the same controller. In Storage Manager you can map a volume to use a specific controller which will help in this kind of a situation.

ftp://ftp.compellent.com/SOFTWARE/SCOS/DOCS/SCOS_6.2_USER.pdf

Above is the link to the Storage Center 6.2 Admin Guide and if you go to page 69 you will see where it talks about Advanced Mapping Options. I hope this helps but if you need anything else please feel free to let me know.

Kenny K.

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andre.wibisono
1 Nickel

Re: Active-Active Controllers

Hi Kenny,

Noted. However in my POC, the 2nd volume did not automatically assigned to Controller B. All new volumes I created always went to Controller A.

If I checked under the Controllers, Controller A is the leader. Could the configuration was setup wrongly?

I tried to access the link you provided, it prompted user name and password. I tried to use Anonymous, but it didn't work. Any idea?

I also have another question: I noticed that I cannot power on single controller only during initial boot up. Both controllers must be powered on together. Otherwise, it won't work. Is that the correct behavior?

I spoke with Dell representative here, and he told me that's the behavior. Both must be turned on together.

I am thinking of a situation where it is not possible to turn both controller (e.g.: due to power failure/controller failure) and only single controller that can be turned on. With current situation, I won't be able to use my storage then.

Your advise please. Thanks very much.

Andre

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mtanen
2 Iron

Re: Active-Active Controllers

In the Compellent Architecture, both controllers are active. Failover is done at either the port or controller level depending on how the system was installed. Volumes are "owned" by a specific controller for the purposes of mapping to servers. Changing the owning controller can be done - but it does take a volume down. The controller generates the choices for mapping based on the topology database that it has built based on connections to the server. If there is a setup problem such that one controller can not see a server, then it wont choose that path as an option by default (this might also indicate a setup problem since its a dual path - dual controller environment you should be able to see the server from both controllers. Views from the same volume object will be owned by the same controller. So if you create a gold master boot and use Replays to deploy it to 20-30 servers - all of their boot volumes will come from the same controller.

It is possible to turn on a single Compellent controller to bring a system back online. If the controller you turn on was not the leader pre-shutdown, you may have to ask CoPilot to help you with the command to promote it. Different versions of Compellent firmware work differently in this case - its how split brain is handled.

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