CiSCSI SettingsThis appendix lists recommended and required settings when using iSCSI cards.Flow Control SettingsThis section provides information about flow control and the recommended flow control settings.Ethernet Flow Control802.3x flow control is a mechanism for temporarily pausing data transmission when a NIC, an HBA port,or a switch port is transmitting data faster than its target port can accept the data.Ethernet flow control allows a switch port to stop network traffic between two nodes by sending aPAUSE frame to another switch port or edge device. The PAUSE frame temporarily pauses transmissionuntil the port is again able to service requests.Switch Ports and Flow ControlRecommendations for using Ethernet Flow Control depends on the switch port hardware.• Ethernet Flow Control should be set to ON for switch ports connected to Storage Center storagesystem card ports.• Switch port settings for server NICs and other switch ports in the switch network should be set to ON.Flow ControlDell recommends the following settings as best practice when enabling flow control:• A minimum of receive (RX) flow control should be enabled for all switch interfaces used by servers orstorage systems for iSCSI traffic.• Symmetric flow control should be enabled for all server interfaces used for iSCSI traffic. StorageCenter automatically enables this feature.NOTE: To find best practices for iSCSI SAN switch configuration, go to the Switch ConfigurationGuides page.Jumbo Frames and Flow ControlSome switches have limited buffer sizes and can support either jumbo frames or flow control, but cannotsupport both at the same time. If you must choose between the two features, Dell recommendschoosing flow control.NOTE: All the switches listed in the Dell Storage Compatibility Matrix support both jumbo framesand flow control at the same time.However, if you use jumbo frames, be aware of the following:• To simplify troubleshooting initial deployments, make sure that all servers, switches, and storage arefully operational before enabling jumbo frames.• All devices connected through iSCSI must support 9K jumbo frames or larger.iSCSI Settings 179
