iSCSI数据传输数据包开销 [英] iSCSI data transport packet overhead

问题描述

这个问题与 iSCSI Packet Header 重叠，但是我希望提供一个比所提供的更具体的答案对于那个我更具体的问题.

This question is admittedly overlapping with iSCSI Packet Header but I hope for a more specific answer than provided for that one for my more specific question.

问题:在读取或写入数据的传输中，iSCSI和SCSI引入了多少开销?

Question: How much overhead is introduced by iSCSI and SCSI in the transfer of the data to read or write?

我知道这是在数据输入和数据输出传输数据包中完成的，并且我知道TCP/IP和以太网会产生开销，但是iSCSI/SCSI需要额外的开销吗?我知道SCSI协议数据单元(PDU)是通过某种算法打包到TCP数据报中的，但是我不确定该算法.

I understand that this is done in the Data-In and Data-Out transport packets and I understand there is overhead from TCP/IP and Ethernet, but what additional overhead is needed by iSCSI/SCSI? I recognize that SCSI Protocol Data Units (PDU) are packed into TCP datagrams by some algorithm, but I'm unsure of that algorithm.

我意识到发起者和目标之间需要进行完整的对话，而我将忽略这一部分.因此，我只想知道在执行读或写命令后发送的数据包.

I realize there is a full conversation that needs to happen between the initiator and target and I will ignore that part. So, I only want to know about the data packets sent following a read or write command.

推荐答案

阅读以下内容是正确的.但是对于写操作(如果未启用立即数据)，目标需要额外的字节来发送另一个称为R2T的PDU，即48字节.由于大多数iSCSI连接都是本地的，并且TCP/IP具有CRC，因此很少使用摘要.

For a read the below is correct. But for a write (if immediate data is not enabled) there are extra bytes required for the target to send another PDU called R2T which is 48 bytes. The digest is rarely used because most iSCSI connections are local and TCP/IP has a CRC.

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