iSCSI performance considerations

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Set the following configurations to get the best performance from iSCSI.

To ensure the best performance:
  • Enable the TCP Large Send, TCP send and receive flow control, and Jumbo Frame features of the AIX® Gigabit Ethernet Adapter and the iSCSI Target interface.
  • Tune network options and interface parameters for maximum iSCSI I/O throughput on the AIX system as follows:
    • Enable the RFC 1323 network option.
    • Set up the tcp_sendspace, tcp_recvspace, sb_max, and mtu_size network options and network interface options to appropriate values.
      The iSCSI Software Initiator's maximum transfer size is 256 KB. Assuming that the system maximums for tcp_sendspace and tcp_recvspace are set to 262144 bytes, an ifconfig command used to configure a gigabit Ethernet interface might look like the following: 
      ifconfig en2 10.1.2.216 mtu 9000 tcp_sendspace 262144 tcp_recvspace 262144
    • Set the sb_max network option to at least 524288, and preferably 1048576.
    • Set the mtu_size to 9000.
    • For some iSCSI targets, the TCP Nagle algorithm must be disabled for best performance. Use the no command to set the tcp_nagle_limit parameter to 0, which will disable the Nagle algorithm.

For more information and additional tuning parameters, see TCP and UDP performance tuning.