It can be used to transmit data over local area networks LANs , wide area networks WANs , or the Internet and can enable location-independent data storage and retrieval. It is a storage area network SAN protocol, allowing organizations to consolidate storage into storage arrays while providing clients such as database and web servers with the illusion of locally attached SCSI disks. By doing this, iSCSI takes a popular high-performance local storage bus and emulates it over a wide range of networks, creating a storage area network SAN. Although iSCSI can communicate with arbitrary types of SCSI devices, system administrators almost always use it to allow servers such as database servers to access disk volumes on storage arrays.
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It is also an error for an initiator to send more unsolicited data, whether immediate or as separate PDUs, than FirstBurstLength. The target reports the same error when the amount of data sent as a reply to an R2T does not match the amount requested. Text requests and responses are designed as a parameter negotiation vehicle and as a vehicle for future extension. The initiator uses the F Final flag bit in the text request header to indicate its readiness to terminate a sequence.
The target uses the F Final flag bit in the text response header to indicate its consent to sequence termination. Text Request and Responses also use the Target Transfer Tag to indicate continuation of an operation or a new beginning. A target that wishes to continue an operation will set the Target Transfer Tag in a Text Response to a value different from the default 0xffffffff.
An initiator willing to continue will copy this value into the Target Transfer Tag of the next Text Request. If the initiator wants to restart the current target negotiation start fresh will set the Target Transfer Tag to 0xffffffff.
Although a complete exchange is always started by the initiator, specific parameter negotiations may be initiated by the initiator or target. The iSCSI Target Server was observed to disconnect the session after it received a Text Request during a normal session, when the following conditions existed:.
Discovery-session - a session only opened for target discovery. All other requests MUST be rejected. The target MUST silently ignore any non-immediate command outside of this range or non-immediate duplicates within the range. During the discovery session, the iSCSI Target Server sends a response code of 0x00 success in response to a logout request with reason code 2 remove connection with recovery.
When receiving a Logout Request with the reason code of "close the connection" or "close the session", the target MUST terminate all pending commands, whether acknowledged via ExpCmdSN or not, on that connection or session respectively.
If the acceptor sends "Reject" as an answer the negotiated key is left at its current value or default if no value was set. If the current value is not acceptable to the proposer on the connection or to the session it is sent, the proposer MAY choose to terminate the connection or session.
Neither the initiator nor the target should attempt to declare or negotiate a parameter more than once during login except for responses to specific keys that explicitly allow repeated key declarations e.
An attempt to renegotiate or redeclare parameters not specifically allowed MUST be detected by the initiator and target. When it receives the previous parameters twice in the negotiation phase, the iSCSI Target Server proceeds with the login request.
StatSN is advanced after a Reject. Any key not understood by the acceptor may be ignored by the acceptor without affecting the basic function.
Skip to main content. Exit focus mode. The text request timed out and possibly terminated. The text request was answered with a Reject PDU. Related Articles In this article.
iSCSI (RFC 3720)
iSCSI Technology (Overview)
iSCSI Target Implementation Notes