Dell EqualLogic PS6100 series Configuration Manual page 75

Table 23 Link aggregation types
Link aggregation type
Static
LACP
PAgP
Vendor Proprietary
Using a LAG to Connect Stacked Switches
7.2.1.3
In some situations it may become necessary to expand the EqualLogic SAN by using more than one
single switch stack. For example, you can link multiple stacks by creating a multi-link LACP based LAG
between the switch stacks. A simplified stack plus LAG switch configuration is illustrated in Figure 20.
You should consider the following recommendations when designing this type of SAN:
•
If possible, use 10Gb connections for all links between each stack.
•
Distribute the links across multiple switches within each stack (this is known as a "cross-
stack" link aggregation group).
•
Use LACP or another type of dynamic link aggregation protocol.
•
Perform tests to determine the best hashing algorithm to use within the link aggregation
group (port channel).
Note: A multi-stack SAN infrastructure as described in this section may provide added
reliability to the SAN environment. But, it may also introduce additional latency and the
potential for lower throughput. The SAN designer will have to carefully consider the
performance and reliability implications.
March 2013
Notes
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.
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.
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.
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 an EqualLogic SAN.
Dell EqualLogic Configuration Guide v14.1 7-66