Creating links in vggroup

[B.S.MANI]

HI friends,
I would like to know about creating links between disks in a vg .If we create a link
what way it would be use usefull also please explain with example

Generally i would like to know abt the link

Thanx in advance
bsm

[Satish Y]

Hi Mani,

You can specify physical volume(PV) links for a physical volume providing DIFFERENT PATHS that reference the SAME PV. In PV arguments the first path becomes the primary link to the PV, the second becomes an alternate link to the PV. The primary link is the default path used to access the physical volume. If the primary link becomes unavailable, LVM automatically switches to the alternate link to access the PV.
But u CANNOT create links between two different disks.

In below example, /dev/dsk/c3t0d0 becomes the primary link to the physical volume. /dev/dsk/c4t0d0 becomes an alternate link to the physical volume.

# vgcreate /dev/vg00 /dev/dsk/c3t0d0 /dev/dsk/c4t0d0

Hope you got it.

Cheers...
Satish.

[Byron Myers]

Besides fault tolerance, manual load balancing can be used with pv-links. For example, if you have two paths, say c1 and c2 to the same 4 disks, then use the c1 (controller 1) disks to access two disks - the pv-links here will be on c2 (controller 2). The other two disks go on c2 for the primary and c1 for the pv-links. This load balances access to two disks on c1 and the other two disks on c2.

[Charles McCary]

If already assigned vgchange can be used to change which path is primary / alternate - check out the man on vgchange