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What magic does the setboot command do?

What magic does the setboot command do?

I've been trying to gain a better understanding of the setboot command which I always considered to be straight forward with little mystery.

 

The question came up first when we were implementing DRD’s on our systems for the first time.

After syncing the DRD (a SAN LUN) we didn’t want to run the drd activate command since we didn’t want the drd to become the primary path.

After some research we found that all drd activate does is run setboot –p on the drd path so we found that we could use setboot –h to get the disk working.

 

Once setboot –h was run you could reboot, select the HA path and the DRD would boot but if you resynced the DRD and rebooted again without running either drd activate or setboot –h again the system isn’t able to boot from the DRD.

 

So the question is, since the boot path isn’t changing between sync’s and it’s still set in the EFI after a reboot what does running setboot –h and pasting in the same boot path do that makes the system realize it can boot from that drive?

 

Thanks,

Travis

1 REPLY
Patrick Wallek
Honored Contributor

Re: What magic does the setboot command do?

Good morning Travis,

 

I don't know if Bill forwarded my e-mail along, but here are my thoughts on this:

 

First -- What exactly happens when you try to boot the system from the DRD disk after a sync and do not rerun 'setboot -h'?  What types of messages are displayed?

 

I assume the steps you are doing are:

 

Run a drd clone

Run setboot -h to set the HA boot path

Reboot and boot from the HA path

Verify drd clone booted success fully

Reboot  and boot from the primary boot path

Resync the DRD clone disk (the same disk as specified in the HA path)

Reboot and boot from the HA path -- It sounds like this is where it is failing unless they run 'setboot -h' or 'drd activate' after the previous step.

 

As far as I know there is nothing special about the setboot command.  It should not matter if you resync the DRD image in between test boots of the DRD disk.  Once the path is set it should work as long as the disk you are booting from is valid.

 

Perhaps setboot reads something from the disk when it is run and that is added to an NVRAM location.  If the act of syncing the DRD image changes something on the disk that setboot, or the boot process, looks for then that could have an impact.  I can't think of what that would be though.