[dm-devel] Changing SAN vendors

[Allen, Jack]

  _____  

From: Allen, Jack 
Sent: Tuesday, February 03, 2009 6:45 PM
To: dm-devel at redhat.com
Subject: [dm-devel] Changing SAN vendors



Hello: 
        Our IT group has decided to switch SAN Vendors. The switch over
for a couple of systems has gone fine, but I have some questions on some
things that have changed.

        First a little information on how the switch over is taking
place. The old SAN is a EMC CX and the new SAN is a HP XP. The system is
connected to a SAN switch which is then connected to both SANs. We shut
down the system, and then rezone the switch/SAN to access the XP now
instead of the CX. The XP passes through all the I/O request to the CX.
When we know the data can be seen correctly, they do some commands that
copies the data from the CX to the XP and then the I/O takes place on
the XP from that point on. All this works fine.

        When only connected to the CX, I had /dev/mapper/mpath1 and
/dev/mapper/mpath2. After the reboot and rezoning /dev/mapper/mpath1 and
/dev/mapper/mpath2 are gone and /dev/mapper/mpath3 and
/dev/mapper/mpath4 are there. LVM finds the Volume Group and all Logical
Volumes with no problem.

        My question is what do I have to change in some configuration
file or what ever to make /dev/mapper/mpath1 and /dev/mapper/mpath2 be
in place instead of /dev/mapper/mpath3 and /dev/mapper/mpath4?

        I know this is not creating any real problem, but it is kind of
misleading, because it looks like 2 paths are missing.

----- 
Thanks 
Jack Allen 
=================================================================

    Well no one replied, so I will answer my on question in hopes that
it may help someone else. But I will ask another question and hope
someone will reply to it, because I have goggled and can not find the
answers.

    The Answer: The friendly names are kept in
/var/lib/multipath/bindings. Because the WWID changed multipathd created
new entries. All I had to do was remove the entries for the old WWID and
change the friendly name for the new WWID. Simple, but hard to locate
the file when no documents I could find to begin with tells you that is
where the friendly names are kept.

    The Question: The first system was running RH EL 5.2, but the next
system is running RH AS 4.7. There was no /var/lib/multipath directory,
therefore no bindings file. So I created both, and entered mpath0 and
mpath1 with the WWID, but it still uses mpath2 and mpath3. I know
multipathd are different version between the two RH Release. Is there
something else I need to change on the RH AS 4.7 system to make it use
the mpath0 and mpath1 names?

-----

Thanks:

Jack Allen

 

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