Changing SAN vendors

Changing SAN vendors

[Allen, Jack]

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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 


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RE: Changing SAN vendors

[Allen, Jack]

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  _____  

From: Allen, Jack 
Sent: Tuesday, February 03, 2009 6:45 PM
To: dm-devel@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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Re: Changing SAN vendors

[Tore Anderson]

* Allen, Jack

>     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?

I suggest you configure the names statically in /etc/multipath.conf
instead, this will work in both RHEL 4 and 5.  This will also allow you
to give the devices more descriptive names than just "mpathN".  For
instance:

multipaths {
  multipath {
    wwid 36006016034301f00b8934c11c241dd11
    alias oracle
  }
  multipath {
    wwid 36006016034301f001c578c8bab21dd11
    alias varwww
  }
}

Regards,
-- 
Tore Anderson
Redpill Linpro AS - http://www.redpill-linpro.com/

RE: Changing SAN vendors

[Allen, Jack]

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Hello:
    Still looking for an answer for RH AS 4.7.
 
    No body has any ideas?
 
-----
Thanks:
Jack Allen

  _____  

From: Allen, Jack 
Sent: Thursday, February 05, 2009 5:03 PM
To: device-mapper development
Subject: RE: [dm-devel] Changing SAN vendors


 


  _____  

From: Allen, Jack 
Sent: Tuesday, February 03, 2009 6:45 PM
To: dm-devel@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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Re: Changing SAN vendors

[Bryn M. Reeves]

Allen, Jack wrote:
> Hello:
>     Still looking for an answer for RH AS 4.7.
>  
>     No body has any ideas?

The mpath names change because the XP is exporting the storage with 
new WWIDs (multipath-tools name binding is all based on LUN WWIDs). 
The bindings are stored in a file that is normally automatically 
generated and maintained.

I think in your stiuation if you need to preserve the old names, your 
best option is to manually edit the bindings file and copy it between 
the hosts that need to have a common view of the storage.

The default location for the file is /var/lib/multipath/bindings, 
although if you have /var configured as a separate file system you 
should move it to /etc and configure the bindings_file option in 
multipath.conf to avoid problems when initialising multipath devices 
before /var is mounted.

You could also take the steps that Tore suggested and configure 
multipath entries in multipath.conf to map the devices but unless you 
are happy with giving them new names this isn't going to work as the 
current multipath-tools will give undefined behaviour if you use 
"mpathN" style names for aliases defined in multipath.conf.

Regards,
Bryn.

RE: Changing SAN vendors

[Allen, Jack]

 

-----Original Message-----
From: Bryn M. Reeves [mailto:bmr@redhat.com] 
Sent: Friday, February 13, 2009 5:29 AM
To: device-mapper development
Subject: Re: [dm-devel] Changing SAN vendors

Allen, Jack wrote:
> Hello:
>     Still looking for an answer for RH AS 4.7.
>  
>     No body has any ideas?

The mpath names change because the XP is exporting the storage with 
new WWIDs (multipath-tools name binding is all based on LUN WWIDs). 
The bindings are stored in a file that is normally automatically 
generated and maintained.

I think in your stiuation if you need to preserve the old names, your 
best option is to manually edit the bindings file and copy it between 
the hosts that need to have a common view of the storage.

The default location for the file is /var/lib/multipath/bindings, 
although if you have /var configured as a separate file system you 
should move it to /etc and configure the bindings_file option in 
multipath.conf to avoid problems when initialising multipath devices 
before /var is mounted.

You could also take the steps that Tore suggested and configure 
multipath entries in multipath.conf to map the devices but unless you 
are happy with giving them new names this isn't going to work as the 
current multipath-tools will give undefined behaviour if you use 
"mpathN" style names for aliases defined in multipath.conf.

Regards,
Bryn.

===========================================
Thanks.

I do have /var as a separate file system and as you said it may not be
mounted when multipathd first starts. I will mv the bindings file to
/etc and make the change in multipath.conf.

-----
Thanks:
Jack Allen