Switching to alternate link

[kenny chia]

Hi
I have the following message appearing in dmesg many times. I believe the fiber channel link to my FC30 is intermittent
----------------------dmesg-------
ALERT: fcT1 (0, 2037692986, 8/8) Fibre Channel Driver received an interrupt indicating a Link Failure. The Frame Manager Status Register is 0x980010d0.
-----------------------------------

Following is the ioscan output
----------------------------------------
fc 0 8/8 fcT1 CLAIMED INTERFACE HP Fibre Channel Mass Storage Adapter

lan 1 8/8.5 fcT1_cntl CLAIMED INTERFACE HP Fibre Channel Mass Storage Cntl
/dev/fcms1

fcp 0 8/8.8 fcp CLAIMED INTERFACE FCP Protocol Adapter

ext_bus 4 8/8.8.0.255.0 fcpdev CLAIMED INTERFACE FCP Device Interface

disk 3 8/8.8.0.255.0.0.0 sdisk CLAIMED DEVICE DGC C3400WDR5
/dev/dsk/c4t0d0 /dev/rdsk/c4t0d0
-----------------------------

vg01 primary link is /dev/dsk/c4t0d0 and the alternate link is /dev/dsk/c5t1d0
--------- output of vgdisplay -v vg01-----
--- Physical volumes ---
PV Name /dev/dsk/c4t0d0
PV Name /dev/dsk/c5t1d0 Alternate Link
PV Status available
Total PE 21256
Free PE 1
--------------------------------------------

Q:
So far the server has not switched to the alternate link. Will the server switch to the alternate link automatically?
If it does, when will it do so?

[SANTOSH S. MHASKAR]

Hi,

Once u add alternet link to a PV then
server immediately starts using it with main link.
U can check this by using following command.

From one session give following command

# sar -d 1 111

From other session give following

dd if=(some_file) of=/dev/null bs=1024k

where some_file can be any file in filesystem
or a block device file for LV with PV having alternet link,

So no question of switching to alternet link.
However if one of the link fails server use the
available link (either main or alternet).

[Robert Salter]

Hi,

There are timeout settingd for both the lvol and the pv, by doing a lvdisplay og the lovl you'll see what the timeout value is, doing a pvdisplay will give you it's timeout value.You can modify them by using 'lvchange' and 'pvchange' do a man on both to get a better understanding of the setting.

Also, if you're concerned that there may be an intermittent problem with the primary path, you can manually switch it to the alternate path by doing a pvchange -s /dev/dsk/c5t1d0. This will use the alternate path until you reboot the server or set it back to the primary path.

Robert

[Robert Salter]

I apologize for all the misspellings, the brain out ran the fingers.

[Sundar_7]

Kenny,

The default time out value for the PV is 60 secs. When an IO to the LV/PV timesout(i.e not acknowledged with 60 secs), LVM will mark that PV as failed and use the next alternate link.

A very good way to test this would be to schedule a downtime and pull one of the two fibre cables. LVM should detect the failure and switch to the alternate link.

If all of your PVs are accessible, then you know your LVM configuration is good.

Sundar.