What no one ever tells you about cluster hardware redundancy


I was recently reminded about this, so I thought I’d post about it and share the knowledge.  I use mostly HP hardware, so in this setup, lets say we have two HP DL585 servers for use in a Windows cluster.  I also have dual fibre channel interfaces in each server.  Externally lets say we have two separate fibre channel switches.  For storage, its an MSA1500 external fibre channel SAN with over 1TB of RAID storage, partitioned for use in a cluster.  The MSA1500 has dual controllers and each controller has its own fibre chennel interface. 

To connect it all together, each server connects one of its two fibre channel interfaces to one physical SAN Switch.  The MSA1500 SAN controllers each get connected to a separate physical SAN switch.  The goal here is to optomize hardware redundancy and make this configuration as fault tolerant as possible.  But here is where the issue comes in. 

No one tells you that you need special software running on each node of the cluster to handle the hardware redundancy.  If you don’t have this software in place, what you will find is that Windows will see two SAN storage arrays.  One of them will be inaccessible since you can only have one physical connection active.  I had to call HP support and go through several explanations of what I was trying to accomplish with all the hardware redundance before I was told about the software I needed.  Its called MultiIO or “Multi Path IO”.  If you do a search on the HP support website, you will find HP MPIO Basic (there are two versions, basic is fine for most people).  Download this software and install on each node and amazingly you will find that things work much better.  From the documentation I saw, there is no indication of needing this software, but in this kind of highly resiliant configuration it is necessary to use MPIO to control the hardware redundancy. 

About Joe

I am the author of this blog, IT engineer, husband, father, and somewhat of a nerd.

Posted on February 26, 2008, in Products I use, Professional/Tech, Software and tagged , , , , , , , . Bookmark the permalink. Comments Off on What no one ever tells you about cluster hardware redundancy.

Comments are closed.

%d bloggers like this: