topic Re: Removing PP and install Devic maper multipatth in Operating System - Linux

Removing PP and install Devic maper multipatth

MSwift — Tue, 26 Oct 2010 13:48:46 GMT

Greetings!

I am looking to remove EMC PowerPaath and install the device-maper-multipaath (rhel 5). Could someone let me know what steps/conf files things to look into to acheive this?

Thanks

M Swift

Re: Removing PP and install Devic maper multipatth

Jimmy Vance — Wed, 27 Oct 2010 00:04:20 GMT

A good place to start would be http://www.hp.com/go/devicemapper

Re: Removing PP and install Devic maper multipatth

MSwift — Wed, 27 Oct 2010 00:30:18 GMT

The Device mapper rpm already seems installed, but the config seems to use Powerpath now (need to know how to verify that). Also, the Powerpath software shoul be removed and the device-mapper-multipath should be configured. That is what i am looking for. Please Help.

Thanks

MSwift.

Re: Removing PP and install Devic maper multipatth

Jimmy Vance — Wed, 27 Oct 2010 00:33:03 GMT

The link I provided has docs on setting up device mapper. Can't help on the PowerPath stuff

Re: Removing PP and install Devic maper multipatth

Michal Kapalka (mikap) — Wed, 27 Oct 2010 04:16:06 GMT

hi,

check this link :

https://secure.linux.ncsu.edu/moin/RealmLinuxServers/Multipathing

mikap

Re: Removing PP and install Devic maper multipatth

Matti_Kurkela — Wed, 27 Oct 2010 05:58:51 GMT

Instructions for uninstalling EMC PowerPath can be found in its documentation (of course).

The documentation for EMC products is available at the EMC Powerlink website:
http://powerlink.emc.com
(registration required, works best using IE browser)

While you're using PowerPath, your LVM configuration should include a filter expression that makes LVM search for PVs on PowerPath devices (/dev/emcpower*) and local disks only. When you remove PowerPath, you should change that filter to prefer device-mapper multipath devices instead (/dev/mapper/mpath* if you use RHEL default names). Check the keywords "filter" and "preferred_names" in /etc/lvm/lvm.conf.

If you're using Oracle ASM for managing raw database disks, then a similar change must be made to ASM's ASM_DISKSTRING parameter.

While you already have dm-multipath installed, it's probably been disabled by a "blacklist everything" configuration setting in /etc/multipath.conf. Once you have removed PowerPath, your first task is to disable that blacklisting to enable dm-multipath. But that's documented in Chapter 3.1 ("Setting up dm-multipath") of this RedHat document:

http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html/DM_Multipath/index.html

MK

Re: Removing PP and install Devic maper multipatth

MSwift — Wed, 27 Oct 2010 13:30:03 GMT

Thanks.

When we have removed PP and installed DMM should a vgscan discover the vgs? since i assume now that /etc/lvm/lvm.conf would be the metadata file, if we take the PP filter out of the metadata file, we should be able to see all the PVs, which means the VGs will be there with no vgscan needed?? or would it require a reboot which would discover the devices and would also do a vgscan? Please advise...

Best Regards

MSwift.

Re: Removing PP and install Devic maper multipatth

Matti_Kurkela — Wed, 27 Oct 2010 14:18:10 GMT

A reboot would certainly do it, but vgscan should be enough to re-discover the VGs.

Once your configuration is complete, I would recommend that you reboot to verify that the system definitely boots correctly in the new configuration.

If your /var is a separate filesystem (= not part of the root filesystem), you should be aware of this:
https://access.redhat.com/kb/docs/DOC-5544
(RHN account required)

MK

Re: Removing PP and install Devic maper multipatth

MSwift — Wed, 27 Oct 2010 14:44:20 GMT

Thanks Matti!

I will try it. One more question. Is it a must to have Multipathd running to make the Device-mapper to work?

Best Regards

MSwift.

Re: Removing PP and install Devic maper multipatth

Matti_Kurkela — Thu, 28 Oct 2010 06:57:18 GMT

If one of your paths fails, then the multipathd is responsible for monitoring the failed path and telling the kernel when it works again. So yes, multipathd is rather important.

However, there is no problem in restarting multipathd while multipathed disks are in use.

(The dm-multipath module can use existing paths just fine without the help of multipathd, and it can even drop out paths that seem to have failed. But it won't automatically add new paths to existing multipath devices, or resume using failed paths once they've been repaired: that's what multipathd does.)

MK

Re: Removing PP and install Devic maper multipatth

MSwift — Thu, 28 Oct 2010 12:28:48 GMT

Thank you Sir!

MSwift