1-Storage/SAN overview and introduction.

In this post let me talk about an introduction or overview about what is Storage Area Network that is well-known  by (SAN) terminology so that we can know what is the purpose of the SAN and what are the components that build the SAN. As the name imply, the SAN is used for the storage purpose, this means that its main purpose is to provide a way used to exchange data between two devices, at which one device access the other device for storage purpose, this means that one device access the other device to either store/write data at the disks installed on the second device(storage device) or to read data  that is already stored at the disks installed on the second device, so the SAN is used to help the two devices to exchange data between each others via its infrastructure. But before talk about the SAN let’s talk briefly about the other methods used to allow the devices (computer system and storage device) to exchange data (read and write operations). The data can be read or written from or to the storage device in multiple forms:

  1. Block: The block is considered as sequence or collection of bytes or bits and has fixed length or size, so when the computer system need to read or write data from or to the storage device, it use certain I/O protocol to do this task, the protocol that we can use at this situation is block-based I/O protocol (i.e it is a protocol that read or write data from or to the storage device in terms of blocks with fixed length or size), an example for the block-based protocol is Small Computer System Interface (SCSI) protocol, Fibre Channel (FC) and Fibre Channel over Ethernet (FCoE).
  2. File: The file is considered as sequence or collection of data with any length or size, so when the computer system need to read or write data from or to the storage device, it use certain I/O protocol to do this task, the protocol that we can use at this situation is File-based I/O protocol   (i.e it is a protocol that read or write data from or to the storage device as it is with any length or size not required to read the data in terms of blocks with fixed length or size), an example for the File-based protocol is Common Internet File System (CIFS), Network File System (NFS) and Server Message Block (SMB).

There are multiple ways we can use to allow the computer system to read or write data from or to the storage device:

  1. Network Attached Storage (NAS): This storage is used when we need to implement the File-based storage system, this means that we use it when we need to implement simple storage system from both implementation and management point of view, as well when we need to exchange bulk of data, so implementing such storage system is considered as the simplest and less cost method to achieve what we need exactly, so from this explanation we can deduce that the advantages of the NAS storage is to allow exchange bulk of data, easy to implement and manage, and requires low cost to be implemented, example for the File-based protocol is CIFS, NFS, SMB, … as mentioned before, the below figure shows simple topology about the NAS storage:Network-Attached-Storage
  2. Direct Attached Storage (DAS): As the name implies, the computer system or server is directly attached/connected to the storage device, at which the server is attached/connected to the storage device using one of the I/O techniques SCSI, FC, FCoE, …, this means that only this server can exchange data with this storage device, so this server is the only computer system that can read or write from or to this storage device, this means that there is no storage sharing offered at this type, as well if you need to make backup for the data stored at the storage device you need to have additional connection to another storage device so this requires more cost than the NAS storage, so we can deduce that the disadvantages of this type is it requires more cost, not easy neither from both implementation nor management point of view, as well it is not supporting storage/file sharing among the other computer systems/servers  and requires more physical ports and cables to backup your connection, the below figure shows simple topology about the DAS storage: das1
  3. Storage Area Network (SAN): I will mention it in the next section.

The main question here, what is Storage Area Network (SAN) ?

The SAN is a network that is similar to the LAN at case of Ethernet/IP environment but its main purpose is to support the storage services, at which it is considered as a high speed network (i.e it is designed to support data to be exchanged with very high rate) and it consists of computer systems, servers, storage devices and storage elements, this means that it is built  by connecting the servers or computer systems with storage devices via storage elements such as switches, routers and directors, this means that the computer systems/servers and storage devices can communicate with each others via those storage elements, so the benefit here is there is no dedicated or limited connection between one server and one storage device because the SAN can serve any-to-any communication, this means that the servers or the computer systems can read or write data from or to multiple storage devices hence the limitations that we saw with the DAS are no longer valid here, regarding the first disadvantage (requires more cost) still exist here, as well it is not easy neither from both implementation nor management point of view, while the limitations that we mentioned before are no longer valid, the SAN is supporting any-to-any communication this means that storage device can be accessed by multiple computer systems not limited by only one computer system, as well if you need to backup your data, right now you have only one connection to the SAN that allows you communicate with all the storage devices connected to this SAN (as long as no some security limitations) so you can store your data at one storage device and backup the data at another storage device, hence no additional cables or ports are required to do this task, as well the storage/file sharing can be achieved and this is thanks to SAN. The below figure shows simple topology about the SAN storage:   SAN

Hope that the post is helpful.

Regards

Mostafa Hamza

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