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HBAs: Are dual HBAs worth the investment?

We have a 150 server dual-fabric storage area network (SAN) currently in place. That will grow to 350+ servers before year-end. We have 10 terabytes (TB) of HDS arrays, soon to be 20 TB, going through two Cisco directors. Some of our servers have dual HBAs, but many do not. Management is balking at spending the extra funds to go with dual HBAs for all servers, basically saying to live with single HBAs for the time being. What are the pros and cons of this approach, as you see it? We can already see concerns with regard to things like future microcode upgrades, cache upgrades, unplanned outages, etc. What would you recommend (if money were no object)? Thanks in advance.

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A question for your management is what value they place on a specific application or server's availability and uptime. If a particular application or server can be offline and unavailable for some period of time for planned and unplanned outages, then a single HBA might be applicable. On the other hand, if the value of application availability exceeds the costs of an HBA; you need to work with your management so they will understand that the price of an HBA can be less than the cost for downtime. When possible, look for ways to build in redundancy including dual HBAs or network NICs unless there is no business reason or benefit to do so. It is important to consider the potential consequences to your customers and applications users.

Without knowing more details about your particular environment, applications, performance, physical layout, network and availability requirements, I hesitate to make any specific recommendation. However, generally speaking, I would look to see if some level of server consolidation using server virtualization is appropriate to reduce the number of physical servers, and thus, the number of HBAs and associated SAN ports. However, this would be dependent on the application's performance requirements as well as application and business needs for dedicated servers. With server consolidation comes the risk of putting too many eggs (or applications) in a basket (server), so be mindful of high availability and server failover capabilities.

What you may find is that some servers could be consolidated onto a larger, higher performance server with redundant 2 gigabit (Gb) or 4 Gb Fibre Channel (FC) adapters to reduce the total number of servers, and thus, adapters. Another consideration to explore is attaching some of the servers using iSCSI to access FC storage via your Cisco directors or third-party iSCSI-to-FC bridge/gateway/router eliminating the need for FC HBAs on your servers. Of course, you would need to have available Ethernet ports or add additional NICs to your servers if needed, thus there would be a cost tradeoff to consider.

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This was first published in June 2006

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