disconnecting FC cable

[Vic S. Kelan]

Hi
I have a freshly created VG that is connected via FC to a Clariion SAN I am preparing. I would like to pull out the FC cable to re-route it while the server and clarion are still running.

Will I get away with this by just doing a vgchange –a n vg06 and not mess up the volume group

[Steven E. Protter]

I find your approach a bit risky if there is anything on the cable already.

Since the vg is fresh, there may be no problem with the switch.

If this is a duplicate of an existing volume group, I think there may be major trouble with your plan.

I would like a bit more detail to be certain.

If you don't have the cable connected, how did you create vg06? Is there mirroring/pvlinks involved.?

SEP

[Mel Burslan]

if you deactivate the volume group prior to the disconnect, you will most probably get a media disconnect message in the syslog but since no process will try accessing the LUN(s) you should not see any adverse effects.

[Raj D.]

Hi Vic ,

Do you have only the "freshly created " vg on that FC . nothing else.

you can check out with ,

# ioscan -fnC fc
# ioscan -fnC disk [ check the path of the disks , if pointing to that FC ]

#strings /etc/lvmtab [ disks for that vg ]
--------------------------------------------

If yes ,hope you can go ahead like this :
---------------------------------------
1. Check with ioscan , the Fibre cable you are going to disconnect belongs to which FC card.

# ioscan -fnC fc
# fcmsutil /dev/td1 [ assuming td1 is the FC card, check details.]

2. Deactivate the vg.
3. #fcmsutil disable /dev/td1

[ you will get a message in syslog , that its disabled ]

4.Remove the cable and do necessary routing.
5.Connect the cable back ,
6. fcmsutil enable /dev/td1
7. Activate the vg .

Though I hv never done that , hope it will help.

Cheers ,
Raj.

[Sameer_Nirmal]

The LVM configuration gets loaded in the memory during system bootup and is handled by LVM device driver . The configuration is always checked by LVM device driver if it is clean or not. I am not sure about its frequency though.
The PVs under a VG (which is activated) use scsi device driver I/O timeout ( 30 Secs ) to let LVM know about its failure after 30 secs. This causes the error messages coming on console and in syslog. This would cause PV getting offline and you get error doing vgdisplay.

Hence if you de-activate the VG , it won't consider under LVM configuration checking ( mor or less real-time check though ) being offline.

So you can de-active the VG and do you work safely without any worry..

[Sameer_Nirmal]

Oops!!! forgot this
Just make sure other VGs are not using that FC port. Run ioscan and check which PVs (LUN) is attached to that FC. De-activate the VG to those PVs belongs.

[Vic S. Kelan]

HI All,
Thanks for all the help.
SEP, I connected one HBA to the new Clariion only. The only device that is connected by the fiber cable is the disk that makes up the newly created VG. Only that VG will be affected if I pull the FC.

Mel, thanks for the tip!

Raj D, yes I have only the freshly created vg and nothing else on the FC I want to disable, thanks for the steps!

Sameer, thanks no other VG is using this port except the new vg I want to deactivate before unplugging.

[Mahesh Kumar Malik]

Hi

If you have dual FC HBAs and Secure path installed, there is no issue. FC cable can be removed one by one for re-routing. syslog will log error message without affecting the server and SAN.

If HBA is single then you must deactivate vg before removing the cable

Regards
Mahesh

[Raj D.]

Hi Vic ,
Hope you can successfuly do the task now , as got good idea & understanding..

Good luck
and cheers,
Raj.