topic Re: Multipath on Redhat 4.3 in Operating System - Linux

Multipath on Redhat 4.3

OSSGeek — Sat, 20 Jun 2009 07:00:20 GMT

Hi,

I need to setup multipathing on Redhat 4.3 and EVA4000 storage but it seems HP's Multi-path Device Mapper Kit requires Redhat 4.5 and above!

Any help or ideas?

Thanks

Re: Multipath on Redhat 4.3

Colin Topliss — Sat, 20 Jun 2009 08:35:38 GMT

Don't use it?

Why not use the multipath software supplied with Linux - it works fine.

Attached is a doc I used to get mpathd running under RHEL4u2 (though I had to go to 4u4 not long after to get NFS file locking).

The only problems I have come across so far with the new EVAs is the number of paths you now see. We restrict it to the minumum that we can that still provides us with resilience. Had one sysem with 130 LUNs, an EVA that had 8 paths - so that gave me 1040 devices - and that caused me issues with multipath and devices! Juggled it so the total number of LUNs was less that 255 and all was OK!

Colin

Re: Multipath on Redhat 4.3

OSSGeek — Sat, 20 Jun 2009 09:41:28 GMT

Thank you colin for the great howto :-), I'll try it

Re: Multipath on Redhat 4.3

Colin Topliss — Sat, 20 Jun 2009 10:04:07 GMT

If it doesn't work for you then let me know and I'll see if I can work out why. I didn't encounter major issues that I remember....

Re: Multipath on Redhat 4.3

OSSGeek — Sat, 27 Jun 2009 07:12:27 GMT

Thanks colin, I could setup MPIO on a testing server without any problem and now want to set it up on a production Oracle RAC server.

Our ASM disk is defined as a raw device for /dev/sda and now I think I have to change the path to /dev/mapper/mpath0
need some more help how should I do this...

Thanks

Re: Multipath on Redhat 4.3

Colin Topliss — Sat, 27 Jun 2009 09:12:13 GMT

With ASM I don't think it cares. When asm starts up, it scans and notes the ASM stamped LUNs it can find, no matter what the path.

Note that there is a timing issue with the start sequence (if I remember correctly there is no dependancy between ocssd and asm, and sometimes one starts before the other is finished).

Colin.

Re: Multipath on Redhat 4.3

OSSGeek — Sat, 27 Jun 2009 10:04:26 GMT

You mean I don't need to run oracleasm createdisk for new path (/dev/mapper/) ?

Re: Multipath on Redhat 4.3

Colin Topliss — Sun, 28 Jun 2009 16:23:40 GMT

I sure don't remember doing it. If I recall, we added the LUNs with the /dev/sd* path, then scanned them in later (after a reboot) once multipathing was set up. Give it a whirl - the worst that will happen in that it will fail! :-)

Col

Re: Multipath on Redhat 4.3

Matti_Kurkela — Tue, 30 Jun 2009 05:53:42 GMT

You don't need to run "oracleasm createdisk" when changing the path, precisely because this is not a *new disk*. It is just a new *path* to access the same old disk.

In a multipathed configuration, paths may come and go, but as long as each necessary disk is accessible by at least one path, the application/database can keep running.

To make the ASM use /dev/mapper/mpath* devices, please see:
http://www.oracle.com/technology/tech/linux/asmlib/multipath.html

MK