Wednesday, 8 May 2013

Host Integration (Power Path memoir):

Let me introduce you with the lead actors. We have two HOSTs (Solaris) configured for a fresh DB RAC installation, a SAN box (VNX) and finally the protagonist EMC Power Path. Let’s configure raid groups using Unisphrere (the best interface I have ever worked with). Create some LUNs and put them in a new storage group. Connect both SPs to your two SAN switches, also connect you DB servers fibers to these switches. Now do the zoning, it is up to you what type you choose. I have chosen hard zoning for this configuration. Let’s install EMC host agent on both the RAC nodes. Verify the agent status on Unisphere, now the hosts can be added to the storage group. Scan hosts for the LUN visibility. Now install power path for multipathing functionality. Once you have installed PP. You have to make sure that the pseudo names and logical names of LUNs are same on both nodes. This is a mandatory requirement for RAC. However if both machines are freshly build and you haven’t fiddle with host integration, everything will go fine. But if you have assigned and remove LUNs on hosts, then you have to work hard to fix pseudo name matching issue. Yes there are several methods on internet for fixing this mess up, but none of them worked for me.

 What we have done after fooling around for 1 ½ days is to rename the pseudo names. In my case one of my hosts was not getting correct name. You can try your luck and rename each LUN. There is a catch that all the renaming will be based on guessing because whenever you put 2a it will change itself to 2c but when you rename it to 2c it will not set to 2a. So you have to try few combinations and think outside the box to rename all LUNs. Once all LUNs are connected to hosts you can verify their paths by using powermt display dev=all command. All LUNs should have 2 paths access to both SPs. You can verify path status by disconnecting one cable at a time. The corresponding path will be displayed as dead. Now RAC can be configured on the attached LUNs. Here I like to mention that VNX is most amazing unified box I have ever worked with. All of its documentation is easily available and its interfaces and tools are amazingly user friendly. Please share if you have a similar experience.