iSCSI, or Internet Small Computer Systems Interface, is a protocol designed to facilitate data transfer over IP networks between servers and storage devices. By encapsulating SCSI commands within IP packets, iSCSI enables the integration of storage systems into an IP network, effectively allowing data to be managed and accessed as though it were directly connected to the server.
At its core, iSCSI works by taking traditional SCSI commands and encapsulating them into IP packets for transmission across a network. These packets are sent to an iSCSI target, typically a storage device or array, which processes the commands. The target interacts with the storage hardware to read or write data as instructed, then encapsulates the response data into IP packets to be sent back to the iSCSI initiator, usually a server or host that made the original request.
iSCSI Main Pros & Cons
One of the primary benefits of iSCSI is its cost-effectiveness. By utilizing existing IP network infrastructure, iSCSI eliminates the need for specialized hardware like Fibre Channel SANs, which can be expensive. This makes iSCSI an appealing option for businesses looking to build or expand their storage systems without incurring significant additional costs. Additionally, the flexibility of iSCSI allows for straightforward integration into existing networks, enabling scalable and adaptable storage solutions that can grow with an organization’s needs.
One of the main disadvantages of iSCSI, particularly for critical or resource-intensive applications, is its higher latency. This issue arises because wrapping SCSI packets around TCP/IP protocols introduces some overhead. Ensuring quality of service and adequate performance on mixed networks can also be challenging. For example, if your VoIP, software iSCSI, email, and Microsoft Word documents are all using the same connection without some form of QoS (Quality of Service), the results may be unsatisfactory. This is one advantage of Fibre Channel SANs, as they almost exclusively carry disk traffic, minimizing the likelihood of other types of network traffic interfering with performance.
iSCSI Initiator
The iSCSI initiator functions like an iSCSI client. It operates with a PC similar to a SCSI bus adapter, but instead of using a physical cable to communicate with SCSI devices, the iSCSI initiator transmits data over the network. There are two types of initiators:
- Software Initiator: A software iSCSI initiator uses code to emulate iSCSI. This is typically implemented through a software driver that utilizes existing networking hardware to connect SCSI devices to a PC via the iSCSI protocol. Software iSCSI initiators are available for most operating systems, such as the iSCSI Windows Initiator, and are the most commonly used method for setting up iSCSI.
- Hardware Initiator: A hardware iSCSI initiator uses dedicated hardware, usually with integrated software. This type of initiator eliminates the overhead associated with iSCSI and reduces the risk of network interruptions. Consequently, servers using a hardware iSCSI initiator may experience improved performance.
