As SAN fabrics increase in size and complexity they outgrow single switch, ring and mesh topologies. Enter the director-class SAN switch, which when used in a core-edge topology, can offer improved scalability, reliability and advanced features such as security and application support.
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In this interview, SearchStorage.co.UK bureau chief Antony Adshead speaks with Steve Pinder, principal consultant at GlassHouse Technologies (UK) about director-class SAN switch benefits. He also discusses how director-class SAN switches fit a fabric topology and the business drivers behind their increasing popularity.
You can listen to this interview as an MP3 download or a read transcript of the first question below.
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Using director-class SAN switches
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SearchStorage.co.UK: What is a director-class SAN switch and how does it differ from any other storage switch?
Pinder: A director-class storage switch in its most simple description is a switch that has more ports than a standard switch. Most SAN switches -- categorised as edge or midrange switches -- are purchased with 32, 48 or 64 ports, each of which allow connection to a host bus adapter (HBA) or storage array controller port. Director-class SAN switches, however, tend to be configured with at least 128 ports but can contain 512 ports or more.
Director-class SAN switches generally come in a large footprint and have slots where adapter cards can be installed. In this way a customer can purchase a director switch with a lower number of ports for their current requirements and purchase more ports as their requirement grows.
Director-class SAN switches shouldn't be compared only on the number of ports they contain. There are many other factors to take into account when considering a director-class SAN switch. These include price, reliability, serviceability and SAN topology.
Price: Director switches tend to be more expensive per port than standard switches. The additional cost per port pays for the added reliability and performance of the director-class SAN switch.
If you don't want the reliability or additional features of an enterprise-class switch, you can purchase a larger number of midrange switches and get the same number of ports at a cheaper price. This segmentation is similar to the storage array market where vendors categorise their arrays as high end or midrange. The high-end arrays are more expensive per gigabyte, but are once again more reliable and have additional features.
Reliability: Director-class SAN switches are also more reliable. Availability is a key indicator of reliability because it tells us the service availability of the switch. This is usually measured as a percentage, with the Holy Grail being 99.999% availability.
High availability: In order to achieve such high availability, director-class SAN switches are built with high-specification components and are made of parts than can be broken and replaced without affecting the performance of the switch. These are known as redundant or hot-swappable parts.
Serviceability: Serviceability measures what maintenance processes can be carried out on the equipment with the system having to be shut down or rebooted. Director-class SAN switches can have microcode upgraded or downgraded while they're still running. Standard switches must be rebooted when microcode is upgraded.
SAN topology: There are many topologies that can be implemented when configuring a storage network, including single switch, mesh, ring and core-edge. Many of these topologies were used when switch port counts were much lower. Director-class SAN switches allow you to simplify a SAN topology while still allowing a large number of ports to be configured.
Director-class SAN switches also allow for a single switch topology to be configured with up to 500 ports or a core-edge SAN with thousands of ports.