You can refer to EqualLogic array network connectivity design guidelines in this blog post: http://en.community.dell.com/techcenter/b/techcenter/archive/2013/02/05/equallogic-network-connectivity-guidelines-how-many-hops.aspx
In this discussion, I will cover a couple of topologies for connecting servers to an EqualLogic SAN.
Topology 1: Single switching layer
In this topology, servers directly connect to the switches connecting to the arrays. This is depicted first with two switches and then with four.
Topology 1a: Two switches
Topology 1b: Four switches
In the four switch topology, servers access volumes on pools that are closer in the network so there is a lower hop count. This provides better latency for server access to storage. The outer boxes illustrate optimal access mapping for servers to pools. However, servers within one box can access the storage pool in another box at a higher latency level.
Containing server access to pools does not impact application design significantly. For example, in virtualized environments each hypervisor host cluster can map to a single storage pool and not span pools. This keeps fail-over and load-balancing domains for virtual machines within a single manageable host cluster and storage pool. It also reduces the number of iSCSI connections required from hosts to pools and aids security by limiting host access to only certain pools.
This topology can be optimal for deployments up to 48 server hosts depending on:
Topology 2: Dual switching layers
In the second topology, servers connect to the switches connected to the storage via a second layer of switches. This layer is referred to as the access layer for this discussion. Two such topologies are depicted below.
Topology 2a: Six switches
Topology 2b: Eight switches
Also in topology 2b, it would be optimal to have the servers access volumes on pools that are closer in the network to provide a lower hop count.
In either topology, ensure that the aggregate bi-sectional bandwidth between the access layer and storage layer is at least equal to or greater than the aggregate bandwidth of all active array ports. In other words, the sum of bandwidth of all switch interconnect links between access and storage layer must be equal to or greater than the sum of bandwidth of all active array ports. This ensures that switch interconnect links between the layers don’t become a bottleneck for traffic to arrays.
This topology can be optimal for deployments up to 96 server hosts depending on:
The two above topologies are simple models to enable and scale server connectivity to the SAN. A larger hierarchical network model can be designed to scale the number of hosts and arrays even further.
Link to EqualLogic publications: http://en.community.dell.com/techcenter/storage/w/wiki/2631.storage-infrastructure-and-solutions-team.aspx
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