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Chapter 2. iSCSI overview
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2.6.1 Software initiator
Many operating systems have iSCSI software initiators. An iSCSI software
initiator is an iSCSI driver that works with the OS TCP/IP stack, network drivers,
and NICs to provide iSCSI connectivity to other iSCSI devices via the IP network.
Since an iSCSI software initiator depends on the OS IP stack, if the IP stack fails
or is taken down by a user, access to the remote disk is lost. As a result, software
initiators are not ideal for usage to boot the server up. See Figure 2-8.
Figure 2-8 iSCSI software initiator
An iSCSI software initiator is an inexpensive alternative to an iSCSI HBA. It is
used to provide iSCSI support via software instead of a separate iSCSI HBA.
An iSCSI software initiator adds additional workload to the server processor,
TCP/IP stack and network driver to handle the additional SCSI protocol and data
traffic. Since the host CPU is responsible for processing TCP/IP requests, iSCSI
can suffer performance degradation - especially in high traffic settings. This
performance limitation is especially dramatic when compared with Fibre
Channel, which does not have TCP/IP overhead. However, iSCSI software
initiators are a potential fit for casual demands for storage access.
One method to address the performance problem is to increase the speed of
your host processor. Another method is to use a TCP/IP Offload Engine.
IP network
DS300
Server
iSCSI driver
TCP/IP
Network driver
NIC
Applications
Client systems
iSC
SI
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