Alternate disk paths

[Prashant Zanwar]

Hi,
For system to know Alternate path to disks, what additional package is needed to be on the system? Or What kernel driver is taking care of the same?

Regards
Prashant

[James R. Ferguson]

Hi:

The LVM driver handles alternate paths as part of its work. Alternate paths, otherwise known as 'pvlinks' can be seen with 'vgdisplay -v /dev/vgXX'.

Regards!

...JRF...

[Helen French]

No additional packages or special kernel drivers required. LVM take care of it all:

1) Check ioscan -fn output and find out your disks primary and alternate paths

2) Plan load balancing by sharing controllers (decide which controller should be primary for which disk)

3) Create primary paths with vgcreate
4) Create alternative paths with vgextend
5) Check with vgdisplay

[blal]

Hi

If dynamic multi pathing is there in your mind , then I think LVM does not have the feature.You have to go for Veritas.

Regds,
baiju

[Tim Sanko]

Unless you have a Symm (Powerpath will handle failure and load balancing) the best way I know is to use the online Veritas file systems.

We have measured EMC's offerrings and found them to be superior in load balancing.

Tim

[Hai Nguyen_1]

Prashant,

This feature is built into the LVM software. You do not have to do anything to enable it or to make it work.

Hai

[Stuart Abramson_2]

Prashant:

Hai Nguyen is correct. No special software required.

However, you should know in advance which disks are alternate paths, because you have to add them in yourself.

You have to say:

vgcreate vgname /dev/dsk/primary /dev/dsk/alternate.

On EMC disks you can use the "inq" command to tell you which disks are alternates.

On other disks, sometimes you just have to KNOW.

Stuart

[binil]

Hi Prasanth,
We don't reqire to use any additional package for this. HPUX OS will take care of that.

To know the alternate path of disks and confirm we need to use a few commands
1)
#ioscan -fnC disk
Then findout the device files for each disks. Match the addressing scenario cXtYdZ to idntify alternate device files (through alternate path) for the same disk.
2)
If it is already configured using LVM and you just wanted to see only, then issue


#strings /etc/lvmtab

Note: If u want to configure disks freshly for failover/Load balancing ,first you find out the devices files then create/extend volumegroup by giving appropriate address.

Regards
Binil

[Sundar_7]

Prashant,

Good to see you are active these days in ITRC :-)

1) U dont need to have any additional s/w for LVM alternate paths

2) With just LVM, we can only designate one more PV as the alternate links. with EMC powerpath we can designate more than one PV as the alternate path and also dynamic load balancing is possible with EMC powerpath.

3) One thing I would like to add is, to find out if a disk is really a alternate link or an another pv

# echo "0x2008?4D" | adb /dev/dsk/c?t?d?
2008: 669349393 040158183 669349393 1040158184
#
This will list some decimal numbers .

second and 4th are the SPU ID. the one that is ,displayed with uname -i command. the 3rd one is the PV ID and the last one is the VG ID.

if you take two device files and would like to find out if they are two different pvs or both the device files referring to the same PV, then run the above command and compare the PV ID, PV ID will be the same for both the disks

If PV ID is same for both the disks then you can designate one of them as alternate links

Let me know of any questsions

Sundar.