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|How big is too big?|
These initial SANs validated the touted benefits of networked storage. As the growth in the number of deployed ports and switches attests, most users have made SANs an integral part of their storage strategy. Benefits of SAN technology are derived from these three key advantages relative to the previous parallel SCSI technology:
- Enabling of increased distances for connectivity
- Ease of modification and expansion
- Support for a relatively large numbers of devices
Users typically begin to encounter greater challenges when they attempt to grow their SAN environment by two times or greater, or when they consider integrating newer products to interoperate within their existing infrastructure. Two fundamental issues are managing expansion in a nondisruptive manner, and ensuring that the resulting SAN will perform as expected. Among the variety of problems commonly encountered when growing a SAN are:
- Port availability for ISLs
- Planning for access requirements to avoid excessive hop count
- ISL saturation and imbalance
- Conflicting host bus adapter (HBA) capabilities and vendor support in heterogeneous environments
- Disruption to the production environment during transition to expanded design
- Management and security constraints
- Zoning complexities and potential for errors affecting the entire SAN
So what are the design goals to consider? A scalable SAN design has these four traits: the ability to add additional hosts and storage/tape devices without reconfiguring ISLs; the ability to increase port count without increasing hop count; the ability to add nodes with minimal placement criteria and lastly, the well thought-out application of fault isolation technologies, such as autonomous regions and zoning, which prevent a single event from disrupting an entire SAN.
This was first published in November 2003