Dell PS4100 Technical Information download pdf (Page 45)

June 2012 Dell EqualLogic Configuration Guide v13.2 39

clustered storage traffic patterns used by the EqualLogic SAN architecture, switches that

support “cut-through” mode are not suitable for use in an EqualLogic SAN and may actually

result in lower overall SAN performance.

• Support for IEEE 802.3x flow control (passive and/or active) on ALL ports: Switches and

network interface controllers used in an EqualLogic SAN must be able to passively respond to

any “pause” frames received. If possible, you should use switches that have the ability to

transmit “pause” frames to external devices in the event that the device cannot adequately

forward traffic in a timely fashion.

• Support for Jumbo Frames: This is not a requirement. But, the use of jumbo frames may yield

desirable results. Most iSCSI SAN implementations should benefit from using jumbo frames.

The actual impact on SAN throughput when using jumbo frames will depend on your

workload’s I/O characteristics.

• Support for Rapid Spanning Tree protocol (IEEE 802.1w), or Cisco “portfast” functionality if

the SAN infrastructure will consist of more than two switches: For SAN infrastructures

consisting of more than 2 non-stacking switches, R-STP must be enabled on all ports used for

inter-switch trunks. All non-inter-switch trunk ports should be marked as “edge” ports or set to

“portfast”.

• Support for unicast storm control: iSCSI in general, and Dell EqualLogic SANs in particular can

send packets in a very “bursty” profile that many switches could misdiagnose as a virally

induced packet storm. Since the SAN should be isolated from general Ethernet traffic, the

possibility of actual viral packet storms occurring is non-existent. In an EqualLogic SAN, the

switches must always pass Ethernet packets regardless of traffic patterns.

• Support for Inter-Switch Trunking (IST) or Stacking: IST support is required to link all

switches in SAN infrastructure together. For stacking capable switches, the use of stacking

ports for IST is assumed. A good rule of thumb for stacking link bandwidth would be a

minimum 20 Gbps full-duplex.

• Support for vLAN functionality if SAN traffic is to share the same physical switch resources

with other (non-iSCSI SAN) network traffic.

Note: We recommend this strategy for small SAN environments only, where networking device

resources are limited. For larger SANs and datacenter environments we recommend using vLAN

functions only if Data Center Bridging (DCB) is implemented.

• Support for creating Link Aggregation Groups (LAG): For non-stacking switches, the ability to

bind multiple physical ports into a single logical link for use as an inter-switch trunk (IST) is

required. The switch should support designating one or more ports for IST (via Link

Aggregation Groups). The switch should support creation of LAGs consisting of at least eight

1Gbps ports or at least two 10Gbps ports.

4.3.1 Connecting SAN Switches in a Layer 2 Network

When more than one SAN switch is required, each switch connected to the array group members will

be in the same subnet. These switches must be interconnected to provide a single switched Ethernet

Note: For 1GbE SANs, using non-stacking switches to connect three or more EqualLogic

arrays into a single group may negatively impact SAN I/O throughput performance.

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Dell PS4100 Technical Information Page 45