iSCSI存储协议摘要
iSCSI（Internet SCSI）是IEFT于2003年发布的存储协议，至今已经超过10年。相比较已有20年历史的FC协议算是后生晚辈，但却在以飞快的速度蚕食FC SAN的市场份额。目前，几乎所有存储厂商都已经提供基于iSCSI协议的块存储设备、存储解决方案和技术支持。
iSCSI协议的负载数据是SCSI命令，而传输则基于久经考验的TCP/IP协议。参照OSI七层网络模型，iSCSI位于第五层会话层，将第七层的SCSI协议包封装映射到第四层的TCP协议包在以太网上进行传输。
SCSI协议是一种客户端/服务器模式的协议，iSCSI在协议封装上大量沿用了SCSI命令的语义，以及Initiator和Target的概念。在一个交互会话中，会话的发起方称为Initiator，而服务方称为Target。IQN（iSCSI Qualified Name）则是用来标识Initiator和Target身份的唯一标识符。
在部署成本方面，FC SAN需要采购专门的光纤、HBA和Fabric，有些特殊需求下还需要采购昂贵的协议分析仪，iSCSI SAN可以充分利用现有的更廉价的LAN网络资源来进行部署。
在安全性方面，由于iSCSI基于TCP/IP协议，因此可以使用IPSec对传输内容进行加密。iSCSI也可以在登陆阶段使用CHAP对会话双方进行身份认证。
在网络隔离性方面，iSCSI可以直接使用VLAN技术对网络进行逻辑分割，或者直接使用独立交换机对网络进行物理分割。
在软件定义的数据中心里，iSCSI SAN也能够更容易地直接部署在基于OpenFlow的虚拟化网络中，实现软件定义的存储。
受益于以太网技术、HBA硬件卸载技术、iSCSI软件技术的高速发展，iSCSI SAN与FC SAN原有的性能差距正在减小。
- 主流操作系统以及存储厂商能够提供成熟、高性能的iSCSI Initiator多路径支持，能够实现端口聚合和负载均衡，防止单点故障。
- 具备TCP卸载和iSCSI卸载特性得到HBA硬件厂商的广泛支持，使iSCSI SAN可以提供更低延迟的存储服务。
- iSER（iSCSI Extensions of RDMA）基于RDMA技术将CPU在内存复制、U-K通信上的性能损耗降到最低，同时特别针对iSCSI协议在TCP层面进行了优化，大幅提升了iSCSI设备的服务能力。
- 10GbE以太网技术的成熟，使iSCSI SAN满足更严苛的性能需求。40GbE和100GbE的以太网设备也在研发中。DCB无损网络机制使得以太网的冲突概率大大降低，使以太网环境更加适合高速率数据传输，以及更好地QoS，iSCSI SAN也能够减少由于丢包带来的性能损耗。
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The iSCSI storage protocol is a storage networking protocol that enables the transport of storage data over IP networks. iSCSI is used to facilitate data storage and retrieval in storage area networks (SANs). iSCSI storage protocol is a block-level storage protocol that uses SCSI commands to manage storage data. CBD topical products iSCSI storage protocol is widely used in enterprise storage environments.
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The iSCSI storage protocol allows for the transport of data over a network using the SCSI protocol. iSCSI is typically used to connect storage real properties Emmetsburg devices to servers, making it possible to store and access data on a storage device as if it were local to the server. iSCSI can be used to connect a server to a storage array, or to connect a server to a storage device located on another server.
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