I have a novice question about bandwidth on a SAN. I currently have 4 Hewlett-Packard Co. (HP) servers running Windows Storage Server 2003 (WSS2003) on a CX500. All the servers currently have 1 host bus adapter (HBA). I am aware that there is a loss of redundancy issue having only 1 HBA per server. If I were to add a second HBA per server, would I also gain bandwidth on the SAN? I have two 16 port Brocade switches.
I would recommend adding a second adapter for availability purposes and should you get a performance boost, consider that a bonus. In theory, when adding a second storage adapter to a server that is attached to a separate switch and fabric, it should be possible to improve bandwidth. However, there are some other factors to consider, including how the storage is configured, what the application workload is, and where a current bottleneck exists.
For example, if each server accesses a separate unique LUN, while a second adapter would add more bandwidth, you might not see a performance improvement. This would be the case if the LUN is being accessed via a single adapter path as well as if the adapter or the LUN are not the bottlenecks. Another example would occur if each server accesses multiple LUNs. If the LUNs are load balanced across adapters, there is the potential for performance improvement.
You should also consider what other traffic exists on the SAN and the switches. Exercise caution when configuring second adapters (storage or network NICs) on the same PCI bus to avoid bus contention.
This was first published in April 2005