RHEL 5.3 & Multipathing question

Brian O'Mahony brian.omahony at curamsoftware.com
Thu Feb 18 04:37:48 CST 2010



-----Original Message-----
From: Eugene Vilensky [mailto:evilensky at gmail.com] 
Sent: Thursday, February 18, 2010 3:36 AM
To: Brian O'Mahony
Cc: linux-poweredge at dell.com
Subject: Re: RHEL 5.3 & Multipathing question


>Any reason you're not moving straight to 5.4? 5.5 is currently in
>beta.  This is the phase of the 5.x life cycle where major feature
>enhancements are still happening, and some neat enhancements in
>storage and reliability have come of late.

Yep. Other departments dictate the OS level for servers, and I don't have a whole lot of say in it. This is a clearcase 7.1.1 server, which is unvalidated currently (or if it is validate it is at an early point where the SCM team don't feel comfortable moving to it). So my hands are tied. Im still running various rhel3,4,4u6,5.1,5.2 systems as well as Debian 3.0 and 4.0 (not amiind to say the various legacy versions of AIX and solaris.)


>I have two onboard network ports and an Intel NIC with
> two ports. One from each is connected to our lan, and the other on each is
> connected to our SAN network, which is segregated from everything else.
>[snip]
>
> As I was reading more documentation, I came across multipathing, and I am
> wondering if it is needed in my case. The machine is going to be the only
> machine connected to the LUN presented by the PS6000. The LUN is 500Gb, and
> this will be chopped down further using the OS (either ext3 or ext4) into
> 10x50Gb logical volumes.
>

> Is multipath really needed and/or necessary in this case? Why?

Fault tolerance as well as round-robin load balancing.

Consider carefully your business and technical requirements.

Do you want to take advantage of multiple links for better throughput?

Do you care if a NIC/switch/port fails and you lose access to your
storage, lose in-flight data, and potentially corrupting the
filesystem (very unlikely with journaling) as well as application
data?

> I9m looking at setting it up anyways, but im in a bit of a rush and would
> rather not put things I don't fully understand on a production box.

I would not recommend this rationale for not doing something nor for
doing it wrong.

You can get started with some of the following documentation:

The dell tech report is here:
http://www.equallogic.com/resourcecenter/assetview.aspx?id=8727

For a deep dive on Red Hat 5.4 multipathing:
http://www.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5.4/html/DM_Multipath/

For reconfiguring certain settings on Red Hat 5 online, including
resizing LUNs and modifying multipath behavior, see:
http://www.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/html/Online_Storage_Reconfiguration_Guide/index.html

I'm sure there's folks on this list who can answer specific
implementation questions you may have, but those guides as well as the
usual manpages should get you started.

//$0.02
-Eugene



Thanks Eugene. Im going to go ahead with this this morning. Thanks to everyone that replied both on and off list. 


Im sure ill be back with questions later. :)

B


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