Disk Attachment Technology FC vs SAS vs iSCSI

In this article I will try to brief about the methods used for attaching hard disk to servers. Mainly it can be separated into 3 categories as shown below
  •  Fibre Channel (FC)
  •  Serial-Attached SCSI (SAS)
  •  Internet SCSI (iSCSI)


Fibre Channel Disk Attachment

  • Fibre Channel (FC) is a high-speed disk attachment technology primarily used for storage networking.
  • It is designed to connect a large number of storage devices to a number of host servers across a Storage Area Network (SAN).
  • Fibre Channel is a transport Protocol (FCP) which transfers SCSI commands and data over Fibre Channel networks.
  • FC supports a much higher number of devices and much longer cable lengths than SCSI. It has become the preferred disk attachment technology in midrange and large scale data center solutions.
  • Host servers contain one or more FC Host Bus Adapters (HBA).

What is HBA?

HBA stands for Host Bus Adapters which are used for connectivity between servers and SAN Storage.


Serial Attched SCSI (SAS) disk attachment

  • SAS is a computer bus used to move data to and from computer storage devices such as hard drives and tape drives.
  • SAS depends on a point-to-point serial protocol that replaces the parallel SCSI bus technology, and uses the standard SCSI command set.
  • Typical SAS throughput is 6 Gbps full duplex. SAS has the capability to reach 24 Gbps if the host can drive it at that speed. When the first 6 Gbps connection is full, the next 6 Gbps connection is used, and so on, up to four connections.


iSCSI disk attachment

  • iSCSI stands for Internet Small Computer System Interface, an Internet Protocol (IP)-based storage networking standard for linking data storage facilities.
  • By carrying SCSI commands over IP networks, iSCSI is used to facilitate data transfers over intranets and to manage storage over long distances.
  • iSCSI can be used to transmit data over local area networks (LANs), wide area networks (WANs), or the Internet, and can enable location-independent data storage and retrieval.
  • IP SANs are a cheaper alternative to FC SANs. However, the lower cost of iSCSI also implies lower performance and scalability
  • A typical Ethernet network operates at 1 Gbps, whereas an FC SAN can run up to 8 Gbps. However you can improve the performance by using high bandwidth Ethernet Card. Migrating to 10 GbE can significantly increase the performance of an iSCSI infrastructure.