HBA-to-server ratio for high availability

Do we need at least two HBAs per server in a SAN solution?
A best practice for high availability is to use redundancy or multiple adapters whether you are using a SAN, direct-attached, or IP-based storage solution. The question of how many host bus adapters (HBA) per server to have in your storage solution is dependent upon your particular performance and service requirements. If your servers do not need redundant paths to SAN storage, then a single HBA would be sufficient. The decision to use two or more HBAs should be based upon your required level of redundancy. For some applications, having two or more HBAs can be provide better performance and workload balancing, in addition to high availability. With the cost of adapters coming down, if you can afford a second adapter, it's a great way to provide some redundancy that might also have some system maintenance benefits by allowing you to isolate storage paths.
This was first published in September 2004

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