Editing ISCSI (section)

==={{Anchor|ISOE-CARD}}Initiator===
{{Further|SCSI initiator}}
An ''initiator'' functions as an iSCSI client. An initiator typically serves the same purpose to a computer as a SCSI bus adapter would, except that, instead of physically cabling SCSI devices (like hard drives and tape changers), an iSCSI initiator sends SCSI commands over an IP network. An initiator falls into two broad types:

A software initiator uses code to implement iSCSI. Typically, this happens in a [[kernel (operating system)|kernel-resident]] device driver that uses the existing [[network card]] (NIC) and [[network stack]] to emulate SCSI devices for a computer by speaking the iSCSI protocol. Software initiators are available for most popular operating systems and are the most common method of deploying iSCSI.

A hardware initiator uses dedicated hardware, typically in combination with [[firmware]] running on that hardware, to implement iSCSI. A hardware initiator mitigates the overhead of iSCSI and [[Transmission Control Protocol|TCP]] processing and [[interrupt|Ethernet interrupts]], and therefore may improve the performance of servers that use iSCSI.
An iSCSI [[host bus adapter]] (more commonly, HBA) implements a hardware initiator. A typical HBA is packaged as a combination of a Gigabit (or 10 Gigabit) Ethernet [[network interface controller]], some kind of TCP/IP offload engine (TOE) technology and a SCSI bus adapter, which is how it appears to the operating system.
An iSCSI HBA can include [[Conventional PCI|PCI]] [[option ROM]] to allow [[booting]] from an iSCSI SAN.

An ''iSCSI offload engine'', or ''iSOE card'', offers an alternative to a full iSCSI HBA. An iSOE "offloads" the iSCSI initiator operations for this particular network interface from the host processor, freeing up CPU cycles for the main host applications. iSCSI HBAs or iSOEs are used when the additional performance enhancement justifies the additional expense of using an HBA for iSCSI,<ref>{{cite web|url=http://www.chelsio.com/chelsio-demonstrates-next-generation-40g-iscsi-at-snw-spring/ |title=Chelsio Demonstrates Next Generation 40G iSCSI at SNW Spring |publisher=chelsio.com |date=2013-04-03 |access-date=2014-06-28}}</ref> rather than using a software-based iSCSI client (initiator). iSOE may be implemented with additional services such as [[TCP offload engine]] (TOE) to further reduce host server CPU usage.