mknod

[WW451512]

Hi All,

Wanted to know while creating a VG, why is creation of control file, /dev/vgxx/group, required (using mknod command) ?

Appreciate your valuable comments.

[Matti_Kurkela]

Mainly historical reasons/legacy compatibility ("it's always been done like this, and some applications expect it that way"), and because sometimes the sysadmin must choose the correct minor number for the VG and the system does not have a way to auto-detect the correct number.

For example: with Serviceguard, the minor numbers of the cluster VGs must be the same in each cluster node. But when you are setting up the cluster, the system has no way of knowing that the number for a particular VG must be the same as on some other HP-UX system (which will soon be added in the new cluster as another node).

In the latest releases of HP-UX 11.31, the creation of the control file is no longer necessary: the system will auto-create it if the sysadmin has not created it in advance.

MK

[Michal Kapalka (mikap)]

hi,

the simple answer ahy is to read the man page :

man mknod

check this article :

"how to create a VG "

http://forums11.itrc.hp.com/service/forums/questionanswer.do?threadId=1408560

#===========================================

from the man page :

DESCRIPTION
mknod creates the following types of files:

- Character device special file (first SYNOPSIS form),
- Block device special file (second SYNOPSIS form),
- FIFO file, sometimes called a named pipe (third SYNOPSIS form).


mikap

[Bhadresh]

Hi,

To select a particular volume group number or if you want to create the volume group the same way as in releases before March 2008, first create the volume group directory and the group file.

Example
# mkdir /dev/vg01
# mknod /dev/vg01/group c 64 0x010000
# vgcreate -s 8 -l 3 -p 16 -e 63535 /dev/vg01 /dev/dsk/c3t4d0

For more details have a look at following:
http://docs.hp.com/en/lvm-v2/L2_whitepaper_8.pdf

Regards,
Bhadresh

[WW451512]

Hi Again,

"How to create VG" is NOT what I want...It is the significance/purpose of file /dev/vgxx/group created by mknod that I am looking for.

Thanks..

[Viktor Balogh · Accepted solution]

Hi,

see this thread:

http://forums11.itrc.hp.com/service/forums/questionanswer.do?threadId=1342008

"The group special file, or control file, provides the means by which LVM kernel and LVM
commands communicate within the volume group you create."

[N,Vipin]

By creating group file we are defining the menthod of communication to that device. Using this group file kernal will understand the type of device (ex. disk/tape/lan) and type of datatransfer it support (ex. charactor/block.

[WW451512]

Thanks a lot Viktor & Vipin for clearing the query.