Release Notes

PS Series SAN design
38 Dell PS Series Configuration Guide
• Support for unicast storm control: iSCSI in general, and PS Series 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 a PS Series SAN, the switches must always pass Ethernet
packets regardless of traffic patterns. Therefore, the switch should have the ability to disable unicast
storm control response.
• Support for stacking: A switch interconnection is required to link all switches in the SAN
infrastructure together. Some Ethernet switches feature dedicated stacking interfaces. A good rule of
thumb for a dedicated stacking link bandwidth would be a minimum 20 Gbps full-duplex. Depending
on your SAN availability requirements, stacking may or may not be a suitable solution for switch
interconnect.
• Support for VLAN functionality
Note: It is recommended to use a physically separated network dedicated to iSCSI traffic that is not shared
with other traffic. If sharing the same physical networking infrastructure is required, then use Data Center
Bridging (DCB) for PS Series SAN.
• Support for creating Link Aggregation Groups (LAG): For non-stacking switches, or where
stacking of switches does not support your availability requirements, the ability to bind multiple
physical ports into a single logical link for use as an interconnection is required. The switch should
support designating one or more ports for interconnection (via LAGs). The switch should support
creation of LAGs consisting of at least eight 1Gbps ports or at least two 10Gbps ports. Variants of
LAG (such as VLT, or vPC) may also be supported if the feature supports the spanning of data
streams across the interconnect variant. Please consult your network specialist to determine the
capabilities of these interconnect variants. At this time, Dell Networking’s VLT and Cisco’s vPC
support this requirement. Some versions of MLAG may not.
Note: For 1GbE SANs, using non-stacking switches to connect three or more PS Series arrays into a single
group may negatively impact SAN I/O throughput performance.
8.2.1 Connecting SAN switches in a Layer 2 network
PS Series storage requires that the SAN be configured as a single Layer 2 network. Layer 2 refers to the data
link layer in the OSI model (http://en.wikipedia.org/wiki/OSI_model). 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 fabric. Figure 4 shows the two common
methods for interconnecting switches, using either stacking switches or non-stacking switches.
Switch Interconnects