Are Alternate Paths Required for lvextend/lvreduce?

[Craig Johnson_1]

Say you have a VG with multiple paths to each disk:

PV Name /dev/dsk/c75t2d7
PV Name /dev/dsk/c67t2d7 Alternate Link
PV Name /dev/dsk/c68t2d7 Alternate Link
PV Name /dev/dsk/c76t2d7 Alternate Link

Let's say you want to mirror and existing LV to the disk above.  Do you HAVE to do this:

lvextend -m 1 /dev/vg10 /dev/dsk/c75t2d7 /dev/dsk/c67t2d7 /dev/dsk/c68t2d7 /dev/dsk/c76t2d7

I'm thinking that since the alternate paths are already defined at the VG level, it isn't required, and thus:

lvextend -m 1 /dev/vg10 /dev/dsk/c75t2d7

would be equivalent.   Am I wrong?  Help!

[Patrick Wallek · Accepted solution]

You are correct.  You just specify one of the paths, I usually try to use the currently defined primary path, when doing an lvextend to create a mirror.  You could use any of the paths though since they all point to the same disk device / LUN.

[Craig Johnson_1]

Thanks Patrick!   Anyone else have a different opinion?  Really need to be sure.

[Robert_Jewell]

A different opinion?   OK...I dont think chocolate cake is all it lives up to be.

Further confirmation about the answer to your question?  Oh.  Yes, what Patrick states is correct.  Since each alternate link is just a pointer or, well, a link to the actual physical volume, the actions taken on the physical volume will be represented by each device path going to that volume.

-Bob

[Craig Johnson_1]

I've been under the impression this was correct for a long time.  I have a team of senior level *nix admins who don't believe me.  Now I have some backup.  Thanks guys!

[Robert_Jewell]

What they may be referring to is that when you first setup the alternate links you need to run 'vgextend' with all of the alternate device paths.

-Bob