Friday, October 14, 2005

Ethernet Jumbo Frame Configuration Procedure

Ethernet Jumbo Frame Configuration Procedure

No configuration changes are required in the iSCSI driver or in the
Solaris operating system to support jumbo frames. Instead,
configuration changes must be made in the Network Interface Card
(NIC), through the use of the configuration interface and tools that
are provided by the NIC manufacturer. Not all NICs support jumbo
frames, so check with your manufacturer to verify that this feature is
supported. Also, the network equipment (Ethernet switches, routers,
and so forth) between the host and the SN 5400 will have to be
configured to accept jumbo frames, because most equipment does not
support this capability by default.
Performance Improvement Techniques

These are the most likely reasons that iSCSI network performance is
lower than expected:

*

Flow control has not been enabled on the NIC card in the host.
*

Flow control has not been enabled on one or more of the switches
in the Ethernet network that is between the host and the SN 5400.

To see these problems, observe either the retransmit timeout or the
data packets retransmitted counters in the SN 5400. You can also
observe the TCP segments retransmitted counter: issue the netstat -s
command in Solaris.

Many NICs and switches are shipped with pause frames (flow control)
disabled. If you enable pause frames on all Gigabit Ethernet
interfaces (the host system and all network switches), then you will
help reduce dropped packets: a source of significant performance
degradation. By default, pause frames are enabled on the SN 5400 and
are not user-configurable.

If your server uses a Sun Gigabit Ethernet adapter NIC, then use this
procedure to enable flow control (by default, receive flow control is
disabled for the Sun adapter):

1.

Add this line to the /kernel/drv/ge.conf file (by default, this
file does not exist):

adv_pauseTX=1;

2.

Reboot the Solaris host.
3.

Issue this command to verify that adv_pauseTX is set properly:

ndd/dev/ge adv_pauseTX

The NIC should respond with a value of 1.

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