removing alternate links

[M Zubair_1]

Is it safe to remove alternate links while the system is online? Or do I have to bring it down to single user mode?

[Bernhard Mueller · Accepted solution]

You can do that without any problems, since LVM uses the alternate link *only* if the primary fails.

Regards
Bernhard

[John Poff]

Hi,

You can remove them while the system is online. You can even remove the primary links and your alternate link will become the primary. I've done that trick before to do a little load balancing by alternating the controllers for each PV in a VG.

JP

[Bernhard Mueller]

... well, assuming you are not using EMC PowerPath or something similar....

Regards,
Bernhard

[M Zubair_1]

No, no EMC Powerlink..
Thanks all!

[Stefan Farrelly]

Just do it online, vgreduce them, its easy and reliable with no impact on normal running.

[Olivier Drouin]

just dont remove all of your path to the same hardware.

[Todd McDaniel_1]

Bernhard,

I see no reason to suggest that having Powerpath would be detrimental to removing alternate paths.

Regardless of what paths are defined via PVlinks. Powerpath searches the frame for alternate paths to the LUN with little or no regard for what you have defined in /etc/lvmtab or in /dev/dsk and /dev/rdsk.

My understanding, having spoken to my EMC specialist, is that Powerpath is smart enough to find the disk based on its serial number so that you will not lose the path. However, you still need at least 1 path to the disk defined at all times, but any alternate paths can be disregarded on the host side.

What Powerpath sees and what you have defined locally on the host, are not interdependent, except what the OS needs in having at least 1 path defined in the LVOL/VG for its own survival/viability. Save for that one path, Powerpath can determine any other paths to push data down to the LUN.

If you had 8 paths to the LUN, Powerpath would push data down all paths even though only 1 is defined in the /etc/lvmtab for a particular LVOL.

Remember, the whole point of Powerpath is to keep your LVOL up and to use all paths available to utilize the full bandwidth to the disk. It is not a static snapshot as is PVlinks and your /etc/lvmtab. It dynamically looks at all paths all the time.

Hope this helps explain some...