Information Technology Reference
In-Depth Information
What about Datacenter Ethernet or Converged Enhanced Ethernet?
Datacenter
Ethernet
(
DCE
) and
Converged
Enhanced
Ethernet
(
CEE
) are prestandard terms used to
describe a lossless Ethernet network. DCE describes Cisco's prestandard implementation of the
DCB standards; CEE was a multivendor eff ort of the same nature.
Because FCoE uses Ethernet, why use FCoE instead of NFS or iSCSI over 10 Gb Ethernet? The
answer is usually driven by the following two factors:
There are existing infrastructure, processes, and tools in large enterprises that are
designed for Fibre Channel, and they expect WWN addressing, not IP addresses. This pro-
vides an option for a converged network and greater efi ciency, without a “rip and replace”
model. In fact, early prestandard FCoE implementations did not include elements required
to cross multiple Ethernet switches. These elements, part of something called FCoE
Initialization Protocol (FIP), are part of the ofi cial FC-BB-5 standard and are required in
order to comply with the i nal standard. This means that most FCoE switches in use today
function as FCoE/LAN/Fibre Chan nel bridges. This makes them excellent choices to
integrate and extend existing 10 GbE/1 GbE LANs and Fibre Channel SAN networks. The
largest cost savings, power savings, cable and port reduction, and impact on management
simplii cation are on this layer from the ESXi host to the i rst switch.
◆
Certain applications require a lossless, extremely low-latency transport network model—
something that cannot be achieved using a transport where dropped frames are normal
and long-window TCP retransmit mechanisms are the protection mechanism. Now, this is
a very high-end set of applications, and those historically were not virtualized. However,
in the era of vSphere 5.5, the goal is to virtualize every workload, so I/O models that can
deliver those performance envelopes while still supporting a converged network become
more important.
◆
In practice, the debate of iSCSI versus FCoE versus NFS on 10 Gb Ethernet infrastructure is
not material. All FCoE adapters are converged adapters, referred to as converged network adapt-
ers (CNAs). They support native 10 GbE (and therefore also NFS and iSCSI) as well as FCoE
simultaneously, and they appear in the ESXi host as multiple 10 GbE network adapters and
multiple Fibre Channel adapters. If you have FCoE support, in effect you have it all. All protocol
options are yours.
A list of FCoE CNAs supported by vSphere can be found in the I/O section of the VMware
compatibility guide.
Understanding iSCSI
iSCSI brings the idea of a block storage SAN to customers with no Fibre Channel infrastructure.
iSCSI is an Internet Engineering Task Force (IETF) standard for encapsulating SCSI control and
data in TCP/IP packets, which in turn are encapsulated in Ethernet frames. Figure 6.12 shows
how iSCSI is encapsulated in TCP/IP and Ethernet frames. TCP retransmission is used to handle
dropped Ethernet frames or signii cant transmission errors. Storage trafi c can be intense rela-
tive to most LAN trafi c. This makes it important that you minimize retransmits, minimize
