Cisco 2970 - Catalyst Switch Manual de usuario descargar pdf (Pagina 9)

Cisco Catalyst 3750 and 2970 Switches: Using Switches with a PS Series Group

delay introduced by this action is dramatically less than the overhead caused by TCP/IP packet

retransmission.

See your switch and NIC documentation for information on enabling Flow Control, in addition to

Enabling the PortFast Option to Configure STP Edge Ports in this document.

Unicast Storm Control

A traffic “storm” occurs when a large outpouring of packets creates excessive network traffic that

degrades network performance. Many switches have traffic storm control features that prevent

ports from being disrupted by broadcast, multicast, or unicast traffic storms on physical interfaces.

These features typically work by discarding network packets when the traffic on an interface

reaches a percentage of the overall load (usually 80 percent, by default).

Because iSCSI traffic is unicast traffic and can typically utilize the entire link, it is recommended

that you disable unicast storm control on switches that handle iSCSI traffic. However, the use of

broadcast and multicast storm control is encouraged.

See your switch documentation for information on disabling unicast storm control, in addition to

Disabling Unicast Storm Control in this document.

Jumbo Frames

EqualLogic recommends that you enable Jumbo Frames on the switch ports that handle iSCSI

traffic. In addition, if a server is using a software iSCSI initiator and NIC combination to handle

iSCSI traffic, you must also enable Jumbo Frames on the NICs to obtain the performance benefit

(or reduce CPU overhead) and ensure consistent behavior.

Ethernet traffic is transported in units called frames. A standard Ethernet frame allows up to 1500

bytes of data to be transferred in a single Ethernet transaction. Jumbo Frames extend Ethernet

frames to 9000 bytes and allow more data to be transferred with each Ethernet transaction.

A PS Series storage array automatically supports standard Ethernet frames and Jumbo Frames up to

9000 bytes (9018 including the TCP header itself). (This is sometimes referred to as the “Alteon

standard.”) PS Series storage arrays also support path MTU, which is the ability to automatically

detect the maximum frame size between TCP/IP end points.

Note: To take advantage of Jumbo Frames, all devices in the network path between servers and

the PS Series group⎯including the switches and the NICs used to access volumes⎯must

have Jumbo Frames enabled.

Switches configured for Jumbo Frames will support both standard Ethernet frames and

Jumbo Frames. However, if a NIC is configured for Jumbo Frames, but the switch is not,

you may experience inconsistent behavior. The switch will function properly if the frames

are small, but once the NIC attempts to send frames larger than 1500 bytes, the switch will

not be able to handle the frames and will drop them. Also, if some switches are configured

for Jumbo Frames, but others are not, you may experience inconsistent behavior if routing

changes occur after the connection has been established.

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Cisco 2970 - Catalyst Switch Manual de usuario Pagina 9