Following the Storage Connectivity Guides

Just a friendly reminder out there to follow the connectivity guides for your SAN storage arrays.  Either it be EMC, HP, or some other storage vendor, each one has their own connectivity guidelines for different types of hosts and operating systems.  With the current simplicity that many of the storage arrays now have when creating and presenting luns for your hosts, it is easy to overlook the connectivity guides.  Many storage administrators may see the luns on their system, write a few blocks of data to it to test it, and assume that they are done with the storage configuration.  This may not be correct as there many times are additional steps to have your new luns perform optimally on your host and application. 

Each operating system will expect their luns to perform differently, depending on how the OS was written.  For example, using Windows 2003 and earlier with VNX (and formally, Clariion) storage, disks ended up off alignment with the blocks.  Certain blocks on the lun were actually split between two disks, so that any single IO written to them actually consumed 2 IO, one for each disk.  Since these blocks would be used over and over again, these IOs would add up, slowing down the performance of the lun drastically.  Reading the VNX connectivity guides, you would see to run the “diskpart” command in windows to line up the disk before you started to write data to it.  This would enforce the OS to line up the blocks on the disk so that no block would span multiple spindles, increasing the lun performance.

Other times, it comes down to a connectivity issue.  A common issue with some administrators is the “lun z” issue, found normally in Solaris. Some OSes will only work with certain HBAs, or require you to edit configuration files before the lun will work.  Again, all of these details are listed in the connectivity guide.
The connectivity guides are always found on the storage vendor’s website.  For reference, I will list a few here.

HP 3Par StorServ

VNX Connectivity Support by Product -> VNX Series

The connectivity guides for each platform should be follow for each lun that you present to your hosts.  They should also be periodically reviewed over time to find the latest results from the lab R&D and new versions of the software.  Following the Connectivity Guides will allow your storage run as effectivity as it can be and providing your hosts with the best possible storage available.