rfc3720.txt

一个学习iSCSI协议的文档

   The SCSI protocol has been mapped over various transports, including
   Parallel SCSI, IPI, IEEE-1394 (firewire) and Fibre Channel.  These
   transports are I/O specific and have limited distance capabilities.

   The iSCSI protocol defined in this document describes a means of
   transporting SCSI packets over TCP/IP (see [RFC791], [RFC793],
   [RFC1035], [RFC1122]), providing for an interoperable solution which
   can take advantage of existing Internet infrastructure, Internet
   management facilities, and address distance limitations.

2.  Definitions and Acronyms

2.1.  Definitions

   - Alias: An alias string can also be associated with an iSCSI Node.
     The alias allows an organization to associate a user-friendly
     string with the iSCSI Name.  However, the alias string is not a
     substitute for the iSCSI Name.

   - CID (Connection ID): Connections within a session are identified by
     a connection ID.  It is a unique ID for this connection within the
     session for the initiator.  It is generated by the initiator and
     presented to the target during login requests and during logouts
     that close connections.

   - Connection: A connection is a TCP connection.  Communication
     between the initiator and target occurs over one or more TCP
     connections.  The TCP connections carry control messages, SCSI
     commands, parameters, and data within iSCSI Protocol Data Units
     (iSCSI PDUs).

   - iSCSI Device: A SCSI Device using an iSCSI service delivery
     subsystem.  Service Delivery Subsystem is defined by [SAM2] as a
     transport mechanism for SCSI commands and responses.

   - iSCSI Initiator Name: The iSCSI Initiator Name specifies the
     worldwide unique name of the initiator.

   - iSCSI Initiator Node: The "initiator".  The word "initiator" has
     been appropriately qualified as either a port or a device in the
     rest of the document when the context is ambiguous.  All
     unqualified usages of "initiator" refer to an initiator port (or
     device) depending on the context.

   - iSCSI Layer: This layer builds/receives iSCSI PDUs and
     relays/receives them to/from one or more TCP connections that form
     an initiator-target "session".




Satran, et al.              Standards Track                    [Page 10]

RFC 3720                         iSCSI                        April 2004


   - iSCSI Name: The name of an iSCSI initiator or iSCSI target.

   - iSCSI Node: The iSCSI Node represents a single iSCSI initiator or
     iSCSI target.  There are one or more iSCSI Nodes within a Network
     Entity.  The iSCSI Node is accessible via one or more Network
     Portals.  An iSCSI Node is identified by its iSCSI Name.  The
     separation of the iSCSI Name from the addresses used by and for the
     iSCSI Node allows multiple iSCSI Nodes to use the same address, and
     the same iSCSI Node to use multiple addresses.

   - iSCSI Target Name: The iSCSI Target Name specifies the worldwide
     unique name of the target.

   - iSCSI Target Node: The "target".

   - iSCSI Task: An iSCSI task is an iSCSI request for which a response
     is expected.

   - iSCSI Transfer Direction: The iSCSI transfer direction is defined
     with regard to the initiator.  Outbound or outgoing transfers are
     transfers from the initiator to the target, while inbound or
     incoming transfers are from the target to the initiator.

   - ISID: The initiator part of the Session Identifier.  It is
     explicitly specified by the initiator during Login.

   - I_T nexus: According to [SAM2], the I_T nexus is a relationship
     between a SCSI Initiator Port and a SCSI Target Port.  For iSCSI,
     this relationship is a session, defined as a relationship between
     an iSCSI Initiator's end of the session (SCSI Initiator Port) and
     the iSCSI Target's Portal Group.  The I_T nexus can be identified
     by the conjunction of the SCSI port names; that is, the I_T nexus
     identifier is the tuple (iSCSI Initiator Name + ',i,'+ ISID, iSCSI
     Target Name + ',t,'+ Portal Group Tag).

   - Network Entity: The Network Entity represents a device or gateway
     that is accessible from the IP network.  A Network Entity must have
     one or more Network Portals, each of which can be used to gain
     access to the IP network by some iSCSI Nodes contained in that
     Network Entity.

   - Network Portal: The Network Portal is a component of a Network
     Entity that has a TCP/IP network address and that may be used by an
     iSCSI Node within that Network Entity for the connection(s) within
     one of its iSCSI sessions.  A Network Portal in an initiator is
     identified by its IP address.  A Network Portal in a target is
     identified by its IP address and its listening TCP port.




Satran, et al.              Standards Track                    [Page 11]

RFC 3720                         iSCSI                        April 2004


   - Originator: In a negotiation or exchange, the party that initiates
     the negotiation or exchange.

   - PDU (Protocol Data Unit): The initiator and target divide their
     communications into messages.  The term "iSCSI protocol data unit"
     (iSCSI PDU) is used for these messages.

   - Portal Groups: iSCSI supports multiple connections within the same
     session; some implementations will have the ability to combine
     connections in a session across multiple Network Portals.  A Portal
     Group defines a set of Network Portals within an iSCSI Network
     Entity that collectively supports the capability of coordinating a
     session with connections spanning these portals.  Not all Network
     Portals within a Portal Group need participate in every session
     connected through that Portal Group.  One or more Portal Groups may
     provide access to an iSCSI Node.  Each Network Portal, as utilized
     by a given iSCSI Node, belongs to exactly one portal group within
     that node.

   - Portal Group Tag: This 16-bit quantity identifies a Portal Group
     within an iSCSI Node.  All Network Portals with the same portal
     group tag in the context of a given iSCSI Node are in the same
     Portal Group.

   - Recovery R2T: An R2T generated by a target upon detecting the loss
     of one or more Data-Out PDUs through one of the following means: a
     digest error, a sequence error, or a sequence reception timeout.  A
     recovery R2T carries the next unused R2TSN, but requests all or
     part of the data burst that an earlier R2T (with a lower R2TSN) had
     already requested.

   - Responder: In a negotiation or exchange, the party that responds to
     the originator of the negotiation or exchange.

   - SCSI Device: This is the SAM2 term for an entity that contains one
     or more SCSI ports that are connected to a service delivery
     subsystem and supports a SCSI application protocol.  For example, a
     SCSI Initiator Device contains one or more SCSI Initiator Ports and
     zero or more application clients.  A Target Device contains one or
     more SCSI Target Ports and one or more device servers and
     associated logical units.  For iSCSI, the SCSI Device is the
     component within an iSCSI Node that provides the SCSI
     functionality.  As such, there can be at most, one SCSI Device
     within a given iSCSI Node.  Access to the SCSI Device can only be
     achieved in an iSCSI normal operational session.  The SCSI Device
     Name is defined to be the iSCSI Name of the node.





Satran, et al.              Standards Track                    [Page 12]

RFC 3720                         iSCSI                        April 2004


   - SCSI Layer: This builds/receives SCSI CDBs (Command Descriptor
     Blocks) and relays/receives them with the remaining command execute
     [SAM2] parameters to/from the iSCSI Layer.

   - Session: The group of TCP connections that link an initiator with a
     target form a session (loosely equivalent to a SCSI I-T nexus).
     TCP connections can be added and removed from a session.  Across
     all connections within a session, an initiator sees one and the
     same target.

   - SCSI Initiator Port: This maps to the endpoint of an iSCSI normal
     operational session.  An iSCSI normal operational session is
     negotiated through the login process between an iSCSI initiator
     node and an iSCSI target node.  At successful completion of this
     process, a SCSI Initiator Port is created within the SCSI Initiator
     Device.  The SCSI Initiator Port Name and SCSI Initiator Port
     Identifier are both defined to be the iSCSI Initiator Name together
     with (a) a label that identifies it as an initiator port
     name/identifier and (b) the ISID portion of the session identifier.

   - SCSI Port: This is the SAM2 term for an entity in a SCSI Device
     that provides the SCSI functionality to interface with a service
     delivery subsystem.  For iSCSI, the definition of the SCSI
     Initiator Port and the SCSI Target Port are different.

   - SCSI Port Name: A name made up as UTF-8 [RFC2279] characters and
     includes the iSCSI Name + 'i' or 't' + ISID or Portal Group Tag.


   - SCSI Target Port: This maps to an iSCSI Target Portal Group.

   - SCSI Target Port Name and SCSI Target Port Identifier: These are
     both defined to be the iSCSI Target Name together with (a) a label
     that identifies it as a target port name/identifier and (b) the
     portal group tag.

   - SSID (Session ID): A session between an iSCSI initiator and an
     iSCSI target is defined by a session ID that is a tuple composed of
     an initiator part (ISID) and a target part (Target Portal Group
     Tag).  The ISID is explicitly specified by the initiator at session
     establishment.  The Target Portal Group Tag is implied by the
     initiator through the selection of the TCP endpoint at connection
     establishment.  The TargetPortalGroupTag key must also be returned
     by the target as a confirmation during connection establishment
     when TargetName is given.

   - Target Portal Group Tag: A numerical identifier (16-bit) for an
     iSCSI Target Portal Group.



Satran, et al.              Standards Track                    [Page 13]

RFC 3720                         iSCSI                        April 2004


   - TSIH (Target Session Identifying Handle): A target assigned tag for
     a session with a specific named initiator.  The target generates it
     during session establishment.  Its internal format and content are
     not defined by this protocol, except for the value 0 that is
     reserved and used by the initiator to indicate a new session.  It
     is given to the target during additional connection establishment
     for the same session.

2.2.  Acronyms

   Acronym     Definition
   ------------------------------------------------------------
   3DES        Triple Data Encryption Standard
   ACA         Auto Contingent Allegiance
   AEN         Asynchronous Event Notification
   AES         Advanced Encryption Standard
   AH          Additional Header (not the IPsec AH!)
   AHS         Additional Header Segment
   API         Application Programming Interface
   ASC         Additional Sense Code
   ASCII       American Standard Code for Information Interchange
   ASCQ        Additional Sense Code Qualifier
   BHS         Basic Header Segment
   CBC         Cipher Block Chaining
   CD          Compact Disk
   CDB         Command Descriptor Block
   CHAP        Challenge Handshake Authentication Protocol
   CID         Connection ID
   CO          Connection Only