alternate link

[khilari]

Hi guys i have 2 disks in an xp1024 /dev/rdsk/c8t8d2 and /dev/rdsk/c13t4d0
now, i extended the volume group with c8t8d2. Now, how do i add the c13t4d0 as an alternate link to it without initializing it with pvcreate ????

[James R. Ferguson]

Hi Khalari:

An alternate link is only a different path to a physical device. Do NOT use 'pvcreate' as this will obliterate the physical volume!

To add an alternate (pvlink) link, simply do:

# vgextend /dev/vgNN /dev/dsk/cXtYdZ

To promote a secondary link to a primary one, simply 'vgreduce' the *primary* thereby promoting the _secondary_ link to a primary one and 'vgextend' the old primary link again.

The first path to a physical volume represented in '/etc/lvmtab' is the primary; the second path is a secondary.

LVM allows up to eight (8) paths to a single physical device --- one primary and seven (7) alternates.

Regards!

...JRF...

[khilari]

ya but when i do that it says its is not a block special file????... I just got a raw disk..... there is no block device file for it.... How do i get its block device file made inorder to add it to the volume group...

[Tim Nelson]

yes
vgextend /dev/vgxyz /dev/dsk/c13t4d0
or when you create the VG.
vgcreate /dev/vgxyz /dev/dsk/c8t8d2 /dev/dsk/c13t4d0

vgdisplay -v /dev/vgxyz

you will see c13t4d0 as an alt link.

no pvcreate needed, as this is the exact same disk you do not want to overwrite the VG header on the disk.

Food for thought. You first path and alt path do not have the same target and lun number ( t8d2 vs t4d0) it would be a really good practice to present the luns with the same lun number. Doing otherwise is just poor organization and may lead to mistakes.

[Torsten.]

I don't think that

/dev/rdsk/c8t8d2 (probably LUN 62?)

is an alternate to

/dev/rdsk/c13t4d0 (LUN 32?)

or vice versa.

Running "xpinfo" will likely clarify.

[khilari]

i have /dev/rdsk/c13t8d2 not /dev/dsk/c13t8d2, thats the whole point. U r giving me commands which will work with /dsk not /rdsk

[skt_skt]

check with xpinfo and confirm if those paths belogn to same LUN.

we did have same setup earlier. Same lun with two different T and D numbers for two paths.

[Torsten.]

If you don't have all device files, consider to use "insf".

[Siju Vadakkan]

/dev/rdsk/c8t8d2 and /dev/rdsk/c13t4d0 are two different disks.
Alternative link means two paths pointing to the SAME LUN(disk). So here u are having two disks.

rdsk - represents character device and pvcreate and diskinfo accepts character device files
dsk - represents block device file and vgcreate and vgextend accepts only block device files.

-----------------
How to find the alter native
----
#/usr/local/bin/xpinfo -f /dev/rdsk/c8t8d2 | grep CU:LDev

this will give is an output some thing like below

CU:LDev : 00:88
#/usr/local/bin/xpinfo -i | grep 00:88

the above command will give two device names, those are two device files pointing to same device , means alternative link.