Posted by: Denny Cherry
Hopefully by now everyone knows that they should be aligning your disks. Now when you use a Storage Array to present the LUNs to the server you may have the option of offsetting the LUN so that you don’t need to offset the disk. If you don’t plan on using any of the advanced clone or snapshot features within the array then this will be fine to do.
However if you plan on taking a clone, or snapshots, or using some sort of array to array based replication this can cause you some performance problems. The reason for this is that when you offset on the array, it simply creates the first block of the LUN at the 32nd block instead of the first block. This works great for a single LUN. However if you decide to take a clone of the LUN, the clone won’t be aligned as the clone will be copied starting at the first block. If the volume is aligned at the server level, the alignment will be copied to the clone and if the clone is mounted everything will respond as expected. However with the alignment set at the array when you mount the clone performance will not work as expected.
P.S. This is based on an EMC CX array. Different arrays will work differently.