Three common storage technologies and iSCSI protocols

1. Common Storage Technology

Das:direct attached Storage, directly attached storage, the storage device is connected directly to the server via a SCSI interface cable, and the storage device does not have any operating system. It relies on servers, where storage devices stack up hardware devices. Das can also be referred to as SAS (server attached storage, which is servers attached storage).

Das has the following characteristics:

1, Das device does not have any operating system, the file system is located on the server side, so is the block level of data transmission

2, it is connected with the server through the SCSI interface cable, therefore, it will increase the server I/O operation, consume CPU, reduce network and service performance.

3. Data sharing of multiple systems is not supported

Das storage devices are generally suitable for small and midsize businesses

Nas:network attached Storage, network attached storage, NAS is a file-level data storage based on IP protocol, supporting the existing network technology, such as Ethernet, FDDI and so on. NAS devices are completely data-centric, completely isolate storage devices and servers, centralize data management, and effectively free up bandwidth, greatly improving overall network performance.

NAS device is a special data storage server, it embedded system software, can provide NFS, smb/cifs file sharing.

Features of NAS devices:

1, because the NAS device embedded system, so the data is file-level transmission

2, because it is a separate storage server, it is only responsible for data transmission, reduce the server I/O operation, therefore, greatly improve the network performance.

3. NAS supports standard network file system and supports cross-platform storage.

4, the server only stores data, can achieve centralized management data

NAS storage devices for small to midsize businesses

San:storage area Network, a shared high-speed storage network, where storage devices are located on the backend of the server, and the storage devices and servers are generally connected by optical-brazing (FC) switches, so the transfer rate is faster. Of course, it is possible to continue the transmission through the IP network, but this is very demanding for network bandwidth. For Sans, the storage device and the server are completely detached, and the server can be centrally managed through a light-brazing switch (or IP network) connected to various storage devices in different regions.

Features of the San:

1, because the file system is located on the server, itself does not have any operating system, so the data is in a block-level way to transfer

2, because the storage server uses optical interface, so the transmission rate is fast, high

3, can be different areas of the server through the optical brazing switch to connect, centralized management

4, because the storage device is located in different regions, so it can realize the large capacity storage data sharing

Because the component set of SAN Systems is more expensive, it is suitable for large enterprises

There are 2 ways to implement a SAN: one is called Fc-san, the San system is implemented through a light-brazing switch, and the other is called Ip-san, which implements the San system through an existing IP network.

The two ways to implement a SAN are as follows:

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Comparison of three storage technologies

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SCSI protocol

The Scsi:small computer system INTERFACE,SCSI was originally an I/O technology designed specifically for small computer systems, but was widely used to implement DAS and the underlying technology as a SAN due to its architecture and protocol advantages.

All SCSI devices are connected by a bus, which is called the SCSI bus. The SCSI bus is the path through which data is transferred between SCSI devices. The SCSI bus is also known as the SCSI channel. The SCSI bus eventually connects to the SCSI controller, which is also known as the host adapter (HBA), which controls the communication between all devices on the SCSI bus and the calculator. The controller can be either a card that plugs into an available slot, or it can be built into the motherboard.

As a result, the SCSI controller and SCSI devices are connected as shown in the following way:

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A terminator on the end of the SCSI bus is used to reduce the signal that interacts with each other, maintaining a constant voltage on the SCSI chain.

SCSI ID

A standalone SCSI bus can support 8 or 16 SCSI target devices (which can be called target) according to specifications, and each SCSI target device must have a unique identifier (ID) to function correctly. The SCSI ID is actually the address of these target devices.

A narrow SCSI bus allows a maximum of 8, wide SCSI buses to allow up to 16 different SCSI target devices to connect to it. However, the general SCSI controller needs to use an ID, so the ID theory that can be used is less than the actual one.

LUNs

You can also connect multiple logical devices (such as disks, volume groups, and so on) under each SCSI target device (target), so that each logical device has a LUN (Logical Unit number) to identify itself, in order for the system to differentiate between each logical device. Each SCSI ID has a maximum of 32 LUNs, which starts from 0 by default (although 0 is occupied), and each LUN corresponds to a logical device.

SCSI Communication Model

SCSI is a C/s architecture in which the client side is called the Initiator (initiator) and the server is called Target. The SCSI protocol adopts layered thinking, and the SCSI protocol cluster can be divided into four layers from top to bottom: device-specific command set, shared command set, transport protocol, Internet layer. and the SCSI data transfer is done in block mode.

iSCSI protocol

This article is from the "Linux Learning path" blog, so be sure to keep this source http://xslwahaha.blog.51cto.com/4738972/1617781

Three common storage technologies and iSCSI protocols