In the SQL Server communities, it's common to hear people talking about HP SAN, EMC SAN, 3Par SAN, and so on as if there were such things as HP SAN, EMC SAN, etc.
Technically, SAN stands for Storage Area Network, but can be, and has been, used in two different ways. First, outside the storage communities, people often view everything beyond the drive at the OS level as the SAN with no regard to how that SAN is architected or configured as long as that drive is presented from some kind of SAN infrastructure. Typically, this is the way SQL Server professionals talk about SAN.
Within the storage communities, the interpretation is often different. To a storage engineer, there is a distinction between SAN and disk arrays: SAN is the network fabric that is made up of switches that provide your host a point-to-point path/link to the disks on some disk arrays. Disk arrays are the storage devices where physical disks are pooled together and managed by sophisticated software and additional controller hardware.
I personally have tried consciously to stick to the second interpretation, and refrained from using terms such as HP SAN or EMC SAN, primarily because this type of speaking adds no value, but introduces inaccuracies, and can be potentially misleading.
First of all, even if you interpret SAN broadly, it’s still probably wrong, or inaccurate, to speak of EMC SAN or IBM SAN, for instance, because it’s highly unlikely that the SAN environment is entirely made up of the EMC or IBM devices (I have not seen one anyway). The disk arrays may be from EMC or IBM, but the switches are often from Broacade or Cisco, or a mix of switches from different vendors. SAN is not a monolithic piece.
Although SAN in terms of the switch fabric can be a limiting factor, especially when it comes to throughput, disk arrays are often where the disk I/O performance is determined, especially when it comes to disk I/O latency. Identifying from what disk array a LUN is carved automatically puts us in a better position in our performance analysis.
Even if we stop being ‘picky’ and interpret EMC SAN to mean an EMC disk array behind a SAN fabric, the phrase is not specific enough to add as much value as identifying it to be an EMC DMX-3 disk array, for instance. Note that there can be many different models, makes, and versions of disk arrays behind a SAN, and their performance characteristics can be vastly different. It does not help to say that your drive is presented from an EMC SAN because two drives presented from the same SAN can perform very differently even with the same number of drives, same type of drives, and same RAID configuration. Many factors of the disk array heavily influence the performance of LUNs carved from the disk array.
Although different LUNs can be carved from the same disk array and these LUNs can be configured to have different performance characteristics, identifying the disk array allows one to understand why two LUNs of the same configuration have different performance characteristics, or at least gives one an opportunity to look for more information, and make the conversations easier with the storage folks.
Saying that a drive is from an EMC SAN is simply too generic to be useful, even if we are willing to ignore the fact that there is no such thing as an EMC SAN.
