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Activating Second Controller

Harvey Beliveau
Occasional Contributor

Activating Second Controller

Hi All:

Hopefully this is a very easy question - I have an AutoRaid with two controllers. One controller is fully configured as the primary and the system is up and running. At this point, with the system up, is it possible to activate the second controller as the secondary?

Thanks In Advance!

Harvey
4 REPLIES
Robert_Jewell
Honored Contributor

Re: Activating Second Controller

The second controller should already be acting as a secondary. If you run the command # arraydsp -c array_id
you will see info on the two controllers. If your primary controller fails the other will take over (providing the SCSI cabling is correct and you have auto failover set up).

I know that may be a leading answer, but by default your array is setup to failover to the secondary controller in the event of a failure in the primary controller.

-Bob
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A. Clay Stephenson
Acclaimed Contributor

Re: Activating Second Controller

Hi Harvey:

If we are talking about HP-UX then the answer is yes and it is probably already configured to use controller Y as the alternate path during failover. SAM will do this for you automatically. The bad news is that this is the bad way to do this for performance. What you would like to have is both controllers active and data coming into both external scsi ports at the same time.

The best way to do that is to split each of your volume groups into 2 equally sized LUN's
and then stripe all lvols withing that vg across both LUN's. One of the LUN's primary path is thru controller X and the other's is thru Y. The alterate paths are still there for failover but using both external busses really improves throughtput and fully utilizes the 4 internal SCSI busses.

See this thread for more details:
http://forums.itrc.hp.com/cm/QuestionAnswer/1,11866,0x5b6187dc4d7dd5118ff00090279cd0f9,00.html
Clay


If it ain't broke, I can fix that.
Harvey Beliveau
Occasional Contributor

Re: Activating Second Controller

I guess I wasn't asking the right question... good info above though...

We have an AutoRaid with two controllers - the previous configuration (prior to rebuilding the system) had two paths, a primary and alternate, to the VG. In rebuilding the system using SAM, only one path was configured, basically leaving the second controller in a standby mode. Is there a way to add the second path back without rebuilding the array?
A. Clay Stephenson
Acclaimed Contributor

Re: Activating Second Controller

Sure, it's very easy. But since SAM normally does configure the alternate paths you may be ok.
Do a vgdisplay -v /dev/vgxx and look for Alternate Paths; if they are there then you're ok.
If not you simply do an vgextend. Man vgextend and pay attention to the section about a pv_path referring to one of the physical volumes already in the vg - the path you specify then becomes the alternate path.

Just to be safe, I would backup before doing this. Bear in mind, that this will give you failover but will not improve performance. For that you would have to follow the procedure explained above.
If it ain't broke, I can fix that.