Technical information

June 2012 Dell EqualLogic Configuration Guide v13.2 38
• For best performance and reliability, we recommend that all interconnection paths between
non-stacking switches (LAGs) use a dynamic link aggregation protocol such as LACP
4.2.1 Quality of Service (QoS)
Quality of service is described as either of the following:
• The ability to provide different priority levels to different applications, users, or data flows, or to
guarantee a certain level of performance to a data flow.
• A network function implemented in some routers and switches that provides high priority for
certain types of latency-sensitive traffic (for example, VoIP) and lower priority for other types
of traffic (for example, web or http).
PS Series arrays are designed to provide I/O as fast as your network can support it. Therefore, using
QoS with iSCSI traffic does not produce expected or desirable results on the SAN. Also, QoS rules can
affect how well–or even whether–replication succeeds between PS Series groups. If you plan to use
QoS, Dell recommends that you use it only on VLANs that do not carry iSCSI traffic, or on WANs,
where bandwidth is shared with other applications and the PS Series array uses it for time-insensitive
replication traffic.
Dell recommends against using QoS on the SAN.
4.3 Ethernet Switches and Infrastructure
Any switch used in an EqualLogic SAN should meet the requirements listed in this section.
Note: A detailed and frequently updated list of recommended switches is maintained in a separate
document:
Validated Components List for EqualLogic PS Series SANs
http://www.delltechcenter.com/page/EqualLogic+Validated+Components
Note: The FS7500 NAS appliance requires the use of 1Gb switches that meet the requirements in
this section, and provide ports that can support dual 1000/100Mbs link speeds .
An EqualLogic SAN consists of one or more hosts connected to one or more PS Series arrays through
a switched Ethernet network. To support a high performance Dell EqualLogic SAN, switches must
meet the following general requirements:
• Low latency: Switches with relatively high latency may cause SAN throughput performance to
degrade, and under high load conditions they could increase the risk of dropped connections.
• Non-blocking backplane design: SAN Switches should be able to provide the same amount of
backplane bandwidth to support full duplex communication on ALL ports simultaneously.
• Adequate buffer space per switch port: In addition to supporting data transfers between the
hosts and the SAN, Dell EqualLogic arrays also use the SAN to support inter-array
communication and data load balancing. For this reason, the more buffer space per port that a
switch can provide the better. Due to the multitude of buffer implementations used by switch
vendors, Dell cannot provide definitive guidelines as to how much is enough. Port buffers
should be designed such that data is not lost when traffic reaches extreme levels. Due to the