摘自：
Cisco MDS switches support the iSCSI immediate data and unsolicited data features if requested by the initiator during the login negotiation phase. Immediate data is iSCSI write data contained in the data segment of an iSCSI command protocol data unit (PDU), such as combining the write command and write data together in one PDU. Unsolicited data is iSCSI write data that an initiator sends to the iSCSI target, such as an MDS switch, in an iSCSI data-out PDU without having to receive an explicit ready to transfer (R2T) PDU from the target. These two features help reduce I/O time for small write commands because it removes one round-trip between the initiator and the target for the R2T PDU. As an iSCSI target, the MDS switch allows up to 64 KB of unsolicited data per command. This is controlled by the FirstBurstLength parameter during iSCSI login negotiation phase
上文百度翻译如下：
在登录协商阶段，如果发起程序请求，Cisco MDS交换机支持iSCSI即时数据和主动请求的数据功能。即时数据是包含在ISCSI命令协议数据单元（PDU）的数据段中的ISCSI写数据，例如将写命令和写数据组合在一个PDU中。未经请求的数据是指发起程序发送到iSCSI目标（如MDS交换机）的iSCSI写入数据，该数据在iSCSI数据输出PDU中，无需从目标接收显式准备传输（R2T）PDU。这两个特性有助于减少小写命令的I/O时间，因为它消除了R2T PDU的发起程序和目标之间的一次往返。作为一个iSCSI目标，MDS交换机允许每个命令最多64 KB的未经请求的数据。这是在iscsi登录协商阶段由firstburstlength参数控制的。