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BP1037 Transitioning to DCB with EqualLogic PS series Storage Solutions 12
3 iSCSI in a converged data center
3.1 Challenge for iSCSI in a shared network
In a traditional, non-DCB Ethernet iSCSI environment, it is a recommended practice to have iSCSI
packets flow in a physically isolated SAN (with dedicated switches/ cabling, etc.), so that the iSCSI SAN
network traffic is minimally affected by other, lower priority Ethernet traffic. In virtualized
environments, it is a recommended practice to employ multiple NICs for traffic isolation (iSCSI,
vMotion, production, management, etc.) The main reason for this is to avoid latency issues,
unpredictable performance and security concerns. The rationale behind this is that sharing iSCSI
network traffic with other traffic causes congestion and competition for limited physical resources in
the network. This results in:
• Packet loss, creating non-deterministic performance
• TCP/IP error recovery is expensive from a predictable latency perspective
3.2 iSCSI TLV’s role in Enterprise iSCSI
For iSCSI SAN traffic to realize the maximum benefit within a DCB based network infrastructure, one
additional requirement needs to be implemented on top of support for PFC and ETS. This additional
capability is part of the DCBx standard and is called “TCP Application Type-Length-Value (TLV)”
support. This form of TLV allows the DCB infrastructure to apply unique ETS and PFC settings to
specific subsets of the TCP/IP traffic stream. This is accomplished by having the switch identify these
various sub-streams based on their TCP “socket” or “port” number which is always available in a
TCP/IP frame.
TLVs based on TCP sockets are not a required part of the standard, but it is very important to iSCSI
storage solutions. iSCSI – as a TCP-based application – has a standard TCP port number (port 3260)
and is specifically known as the “iSCSI TLV”. Over time, switch, NIC, CNA and router vendors who are
dedicated to providing the most efficient and flexible solutions for iSCSI network design, will
implement the iSCSI TLV.
3.3 Enterprise iSCSI solution example
Below is an example for enterprise iSCSI Solution that fully supports DCB. The solution includes the
elements below.
• PowerEdge servers (R710) in VMware cluster
• EqualLogic array (PS6010XVS)
• PowerConnect switch (B-8000e)
• Emulex Enterprise iSCSI HBAs