Release Notes

PS Series SAN design
39 Dell PS Series Configuration Guide
8.2.1.1 Stacking switches
Stacking switches provides a simple method for creating a switch interconnection within a Layer 2 network
infrastructure. Stacking is typically accomplished using a vendor proprietary, high-bandwidth, low-latency
interconnect that allows two or more switches to be connected in such a way that each switch becomes part
of a larger, virtual switch. Most stackable switches will provide a set of dedicated stacking ports or Installation
of an optional stacking module may be required. Some switches also provide virtual stacking modes using
standard Ethernet ports.
8.2.1.2 Non-stacking switches
Non-stacking switches do not have a dedicated switch interconnect. In this case to create an interconnect
between the switches you must utilize one or more ports on each switch to create a LAG. This type of switch
interconnection should use link aggregation functions (if provided by the switch) to aggregate multiple
Ethernet ports into a single, logical high bandwidth interconnect. There are several options depending on the
vendor of the switch. Table 34 describes the most common options.
Note: For best performance and reliability, use a dynamic link aggregation protocol such as LACP for all
interconnection paths between non-stacking switches (LAGs).
Link aggregation types
Link aggregation type
Notes
Static
Static link aggregation defines a set of links that provide a point to point
connection between two switches. These links may or may not provide failover
redundancy or traffic load management.
LACP
Link Aggregation Control Protocol is based on IEEE 802.3ad or IEEE 802.1AX.
LACP is a dynamic LAG technology that automatically adjusts to the appearance
or disappearance of links within the defined LACP group.
PAgP
Port Aggregation Protocol (PAgP) is a Cisco Systems® proprietary networking
protocol, which is used for the automated, logical aggregation of Ethernet switch
ports, known as an etherchannel. This means it can only be used between Cisco
switches and/or switches from licensed vendors.
Vendor Proprietary
Several switch vendors may provide additional link aggregation options that are
completely proprietary or may be extensions to one of the two previously
mentioned solutions. In most cases, this type of link aggregation solution is
designed to reduce or eliminate the need – and the overhead – of the Spanning
Tree Protocol that must be used in the two previous options. If available, these
proprietary options should be considered. They may be very useful in allowing the
network administrator to create a more efficient multi-switch layer 2 network
infrastructure for a SAN. Be aware that these proprietary solutions must support
the transmission of IEEE 802.1x flow control and jumbo frames (if used) to
properly support a PS Series SAN.
Examples of this type of interconnect include Dell Networking or Force10 Virtual
Link Trunking (VLT) and Cisco Virtual Port Channel (VPC).