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.
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.
This was first published in April 2010