Dell Compellent Series 40 - Manual (Page 179)

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Viewing iSCSI Cards
Enabling Jumbo Frames
Note Not all cards support Jumbo Frames.
Enabling Jumbo Frames in the Storage Center controller can enhance network throughput
and reduce use of the CPU. A Jumbo Frame is 9000 bytes compared to normal size of 1500
bytes. Throughput for large file transfers, such as large multimedia or data files, is
increased by enabling larger payloads per packet. Larger payloads create more efficient
throughput and require fewer packets to be sent. Environments with ISCSI servers running
software initiators using standard or smarter NICs receive the biggest benefit from Jumbo
Frames. Enabling Jumbo Frames can speed up iSCSI performance by about 5 percent,
while reducing server CPU utilization by 2 percent to 3 percent.
Jumbo Frames are recommended only for LAN environments. Because TOE (TCP off-load
engine) cards or HBAs already do off-loading, CPU savings from Jumbo Frames is minimal.

To enable Jumbo Frames
1 In the system tree, select an iSCSI card.
2 From the shortcut menu, select Properties. The IO Card General Properties window
appears.
3 Set the Maximum Transmission Unit to 9000.
4 Click OK.
Enabling VLAN Tagging
Note Not all cards support VLAN tagging.
A virtual local area network (VLAN) is configured on a system switch. The four prominent
VLAN membership methods switches support are by port, Media Access Control (MAC)
address, protocol type, and subnet address. A VLAN consists of a network of computers
that behave as if connected to the same wire - even though they may actually be physically
connected to different segments of a LAN. Traffic on a single physical network can be
partitioned into virtual LANs by tagging each frame or packet with extra bytes to denote
which virtual network the packet belongs to. Several VLANs can co-exist within such a
network. This reduces the broadcast domain and aids network administration by separating
logical segments of a LAN (such as ISCSI SAN traffic).
System Manager does not know or need to know how VLAN membership is configured on
a switch. The Storage Center ISCSI I/O port is an end station to the VLAN. VLAN can be
enabled or disabled on an iSCSI port. The default is disabled. VLANs:
• Increase the number of broadcast domains but reduce the size of each broadcast
domain, which in turn reduces network traffic and increases network security (both of
which are hampered in cases of single large broadcast domains).
• Reduce management effort to create subnetworks.
• Reduce hardware requirement, as networks can be logically instead of physically
separated.
• Increase control over multiple traffic types.