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
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
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.