Information Technology Reference
In-Depth Information
modern CPU, and the cost of iSCSI HBAs is usually less than the cost of slightly more CPU.
Keep the CPU overhead in mind as you craft your storage design, but don't let it be your sole
criterion.
Figure 6.14
h e iSCSI IETF
standard has
several diff erent
elements.
iSCSI network portal:
192.168.1.100
iSCSI network portal:
192.168.1.200
iSCSI connection (This is a
TCP connection between an
initiator and a target.)
iSCSI
initiator
iSCSI target
iSCSI network portal:
192.168.1.101
iSCSI session (In general, can be multiple
TCP connnections. This is called Multiple
Connections Per Session.)
iSCSI network portal:
192.168.1.201
iSCSI LUN
(In general, there
can be many iSCSI
LUNs behind a
single target,
though some
arrays use one
target per LUN.)
Figure 6.15
Some parts of the
stack are handled
by the adapter card
versus the ESXi
host CPU in various
implementations.
Software iSCSI
initiator with generic
network interface
card
Software iSCSI
initiator with TCP/IP
offload
Hardware iSCSI
initiator (iSCSI HBA)
SCSI port to OS
iSCSI
SCSI port to OS
SCSI port to OS
iSCSI
Host
Processing
TCP/IP
iSCSI
TCP/IP
TCP/IP
Adapter
Card
Adapter driver
Adapter driver
Ethernet
Ethernet
Ethernet
Media interface
Media interface
Media interface
Also note the difference between a dependent hardware iSCSI adapter and an independent
hardware iSCSI adapter. As the name suggests, the former depends on vSphere networking and
iSCSI coni guration, whereas the latter uses its own networking and iSCSI coni guration.
Prior to vSphere 5.0, one thing that remained the exclusive domain of the iSCSI HBAs was
booting from an iSCSI SAN. From version 5.0, vSphere includes support for iSCSI Boot Firmware
Table (iBFT), a mechanism that enables booting from iSCSI SAN with a software iSCSI initiator.
