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How to switch to alternative FC link

aaa_37
Occasional Contributor

How to switch to alternative FC link

Hi All,
I need to know following

1. If there are two FC paths (like c3t0d1 and c4t0d1) between disk enclosure and server, one will be primary and other will be alternate link. How can I switch between these two paths.

2. How can I know which is the primary link and which is alternative link

3. How can I know link is working fine or not

I am using N-Class server with F10 disk enclosure connected with FC.

Thanks in advance.

Venki
5 REPLIES
harry d brown jr
Honored Contributor

Re: How to switch to alternative FC link

Venki,

Do an "iosan -fn >/tmp/ioscan.txt" then "more /tmp/ioscan.txt". Look for the disk c3t0d1 and note the IO path. Do the same for c4t0d1. Then look at the back of your N-class and it will tell you what IO paths are where.

SEE the ATTACHED .bmp file for IO paths.

When you set up your VG you give BOTH paths (ie c2t0d1 and c4t0d1) and the system will make the first disk PATH primary and the second disk PATH the secondary.


live free or die
harry
Live Free or Die
Andrew_80
Advisor

Re: How to switch to alternative FC link

The way to switch is to do this:
# ioscan >/tmp/io.txt
# vi /tmp/io.txt and look for fcms or td (if you're using the new A5158 cards.
if you want to switch from c3 to c4 You have to disable the card which is connected to C3
# fcmsutil /dev/fcms# disable
OR
# fcmsutil /dev/td# disable
Before you do his look at your vgdisplay to make sure you have both links active, you should see somthing similar to this
--- Physical volumes ---
PV Name /dev/dsk/c3t0d2
PV Name /dev/dsk/c4t0d2 Alternate Link
When you disable the card you will only see c4t0d2 in your vgdisplay, after that you can enable it back
# fcmsutil /dev/fcms# enable


Good Luck
The Sky is the Limit
Virgil Chereches_2
Frequent Advisor

Re: How to switch to alternative FC link

1. You may switch between paths using "pvchange -s /dev/dsk/cxtydz"(see man pvchange) where cxtydz is the device driver of the disk you want to be primary.
2. You can find which of the disks is the primary and which is alternate by looking at the output of vgdisplay -v vgxx command.
3. You may find out the state of the link by looking at the output of "ioscan -fn" command. If something is wrong you will see a NO_HW asociated with the failed path.



Hope that will help,
Virgil.
Insu Kim
Honored Contributor

Re: How to switch to alternative FC link

1.How can I switch between these two paths.
> You can use "pvchange -s " to manually switch access to the device to the path.
or you can "vgreduce & vgextend" as well.

2. How can I know which is the primary link and which is alternative link.

> When you do "vgcreate vg_name ",
The first path will be the primary link to the volume and the second becomes an alternate link.

3. How can I know link is working fine or not

> If link is not working, "vgdisplay" or "dmesg" will show you that link has failure.

Hope this helps,
Never say "no" first.
Johannes_K
Occasional Advisor

Re: How to switch to alternative FC link

Hello all,

the pvchange -s command will lose it??s effect after the next reboot. If You want to swap the order permanently You need to change /etc/lvmtab as follows.

1. From the order of the devicefile in the "strings /etc/lvmtab" output You see primary link above the alternate.
2. swapping can be performed online by vgreduce??ing the primary and vgextend??ing it afterwards again. For example:
# vgreduce /dev/vg01 /dev/dsk/c0t1d4
# vgextend /dev/vg01 /dev/dsk/c0t1d4

This will reverse the order in the /etc/lvmtab. vgdisplay -v will display the result afterwards.