Alternate link for disk: I want to switch this config

[malki_3]

Hello everybody
I have a special configuration on one volum group that I want to improve
vgdisplay vg01
--- Volumes physiques ---
PV name /dev/dsk/c5t0d0
PV name /dev/dsk/c6t0d0 Alternate link
VG name /dev/vg01
..etc
With this configuration I have the second controller not used. It will be actived only when I have a problem with my first link (principal) (correct me if i said mistak)
What I need to do : changing the configuration for this link for possibiliy of load balancing
over two links

--- Volumes physiques ---
PV name /dev/dsk/c6t0d0 Alternate link
PV name /dev/dsk/c5t0d0
VG name /dev/vg01
thinks for yours requests

[Sridhar Bhaskarla]

Hi Malki,

You can use pvchange to change the behaviour temporarily. To make it permanent do a sequence of vgreduce and vgextend on each primary disk that you want to convert to alternate. In your case, you would do

#vgreduce vg01 /dev/dsk/c5t0d0
#vgextend vg01 /dev/dsk/c5t0d0

This will make c6t0d0 as the primary.

-Sri

[Jeff Schussele]

Hi malki,

What you should first do is back it up to be safe - twice would be better
Then what you should do is create the map file - again to be safe
vgexport -m vg01.map /dev/vg01
Then reduce out the current primary vgreduce /dev/vg01 /dev/dsk/c5....
Then re-add the primary - it will now be the alt
vgextend /dev/vg01 /dev/dsk/c5....
Then recreate the map file to reflect the new config
vgexport -m vg01.mapfile vg01

HTH,
Jeff

[James R. Ferguson]

Hi:

Switching alternate (pv) links can be done quite quickly. Simply 'vgreduce' the primary link. This will promote the secondary link to a primary. Then, 'vgextend' (back) the original primary link. It will become the secondary.

# vgreduce /dev/vg01 /dev/dsk/c5t0d0
# vgextend /dev/vg01 /dev/dsk/c560d0

Regards!

...JRF...

[Dan Yeatman]

You can use this method

# vgreduce /dev/vg01 /dev/dsk/c5t0d0
# vgextend /dev/vg01 /dev/dsk/c5t0d0

LVM determines the order - which device file is the primary path and which are the alternate(s) - based on the order the device files are listed in the /etc/lvmtab file. This is a binary file, however the file can be viewed using the "strings /etc/lvmtab" command.

OR using pvchange to temporarily change it

Manually switch a physical volume to use another controller path:

pvchange -s /dev/dsk/c6t0d0

To avoid the possibility of LVM switching back to the primary path, an additional command (called the "autoswitch" flag) can be executed:

pvchange -S n /dev/dsk/c6t0d0

When set to "n" (meaning "no"), LVM will NOT switch back to the primary path

Once the problem is resolved, a "pvchange -S y" will need to be executed to enable "autoswitch" feature for each device that had the autoswitch disabled.

Use "pvdisplay " to view the status of the autoswitch flag as well as other information about the physical volume status.


pvdisplay /dev/dsk/c6t0d0
--- Physical volumes ---
PV Name /dev/dsk/c6t0d0
VG Name /dev/vg00
PV Status available
Allocatable yes
VGDA 2
Cur LV 8
PE Size (Mbytes) 4
Total PE 4340
Free PE 3022
Allocated PE 1318
Stale PE 0
IO Timeout (Seconds) default
>>>>>>Autoswitch On

[Sanjay_6]

Hi Malki,

There is no benefit. LVM does not do load balancing using alternate links. There would be no benefit. you can still change the links from primary to alternate by doing a vgreduce and then a vgextend.

http://us-support.external.hp.com/cki/bin/doc.pl/sid=9f9738c915f1e3167a/screen=ckiDisplayDocument?docId=200000058669314

Hope this helps.

Regds