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** Primary and Alternate Paths for Disks **

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Michael Gretton
Frequent Advisor

** Primary and Alternate Paths for Disks **

Hi all:

If you have been reading some of my questions here and there over the last few months I have been tinker-toying together a VA7400 SAN. I am really almost there and I have built in redundancy by getting another switch. Still waiting on dual HBAs but that must wait.

My question is: I want to create file systems that use LUNs on the VA. I know about the performance issues with Redundancy Groups and I understand that pretty well. I want to use Controller 1 for RG1 LUNs and Controller 2 for RG2 LUNs. How can create these volumes so that I can set a primary path and then an alternate path for some protection? I know that I should to this via the command line. Does someone have a quick recipe? I reading documentation and trying my best but I have an oracle guy coming in a few hours who wants to have everying ready for testing. Thanks in advance.

Ken Hubnik_2
Honored Contributor

Re: ** Primary and Alternate Paths for Disks **

You can use pvchange to change from primary to alternate
pvchange -s /dev/dsk/c#t#d#
Honored Contributor

Re: ** Primary and Alternate Paths for Disks **

Hi, Mike

SAN is really a new area for me.
but in HP we can set the primary and alternate boot path using 'setboot'

#setboot -p disk-path set the disk to primary

#setboot -a disk-path set the disk to alternate

disk-path can be get by using
ioscan -fnC disk
never give up
James R. Ferguson
Acclaimed Contributor

Re: ** Primary and Alternate Paths for Disks **

Hi Mike:

The rule is simple. When a 'vgcreate' or 'vgextend' is done, the first unique physical path to a disk device becomes its "primary" link. The second (or third, etc.) path becomes the "alternate" link.

Thus, the "primary" link is nothing more than the FIRST path to a device as recorded in '/etc/lvmtab'.

To exchange the primary link to a device with its alternate, simply 'vgreduce' the primary path and then 'vgextend' that path back into the volume group. When the 'vgreduce' occurs, the "alternate" link is promoted to a "primary". When the 'vgextend' of the old primary path occurs, the path is noted to point to the same disk as that of another path and so it is added as an "alternate" link.

Thus, the order of paths in 'etc/lvmtab' determines the primary and alternate links to various devices. This is why you are warned when you do a 'vgscan' that the designated primary and alternate link might not be the same as it originallywas configured. (See the man pages for 'vgscan').


Hamdy Al-Sebaey
Regular Advisor

Re: ** Primary and Alternate Paths for Disks **


TO get the alter.link in place of teh prim.link, the simplest way is to use vgreduce.
Thanks for sharing knowledge