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IBM TotalStorage DS300 and DS400 Best Practices Guide
iSCSI full feature phase
After a successful login process, normal SCSI commands, data and messages
can flow. Data and status for a given command must be sent over the same TCP
connection. This is called connection allegiance and is based on port and IP
number. Ordered command sets may use a different connection.
iSCSI data flows
Outgoing data (initiator to target) can be either solicited or unsolicited. Solicited
data must be sent in response to Ready to Transfer PDUs (R2T) from the target.
An initiator can send unsolicited data as part of a command or in a separate
PDU. All subsequent data PDUs have to be solicited.
Figure 2-3 shows the iSCSI data packet frame.
Figure 2-3 Data encapsulation of iSCSI frame
iSCSI connection termination
Connection terminations are exceptional events. Graceful connection shutdowns
occur when there are no outstanding tasks with allegiances to the connection. If
there are outstanding tasks, or tasks that have not yet sent status information,
recovery actions may be needed.
TCP/IP Packet
iSCSI Data Packet
Ethernet
Header
IP TCP
Ethernet
Header
CRC
IP TCP
Data
iSCSI SCSI
CRC
Data
CRC
Preamble
Destination
Address
Source
Address
Type
IP
TCP
Data
FCS
46 - 1500 bytes
8
6
6
2
4
Opcode
Opcode Specific Fields
Length of Data (after 40 byte header)
LUN or Opcode-specific fields
Initiator Task Tag
Opcode Specific Fields
Data Field .....
Source Port
Destination Port
Sequence Number
Acknowledgement Number
Window
Checksum
Options & Padding
Urgent Pointer
Well-known Ports:
21 FTP
22 Telnet
25 SMTP
80 http
5003 iSCSI
iSCSI encapsulated
TCP Header
Summary of Contents for TotalStorage DS300
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