In this article, the next in our series 'Storage Basics', we are going to look at the Small Computer Systems Interface (SCSI). SCSI is a complex subject,
SCSI protocols are standards that exist to define how data is transferred from the data initiator (server) to the storage target (disk array). Until iSCSI, which stands for the Internet Small Computer Systems Interface, came along, it was not possible to transfer SCSI data where the distance between the storage initiator and storage target was ...
SCSI’s 25 meter transmission range is far short of the 10,000 meters offered by Fibre Channel and precludes it from being used in many storage area network applications. In fact, Fibre Channels 10,000 meter limit can be extended to 100 kilometers using special optic transceivers leaving SCSI way behind.
The SCSI bus, parallel in nature, can only support a single communication at a time, so subsequent sessions must wait their turn. SAS, or Serial Attached SCSI, does away with this limitation by automatically switching back and forth.
The SCSI commands are sent to a SCSI controller, and the controller diverts those SCSI commands to the SCSI storage device. The iSCSI protocol is bi-directional and can also return data in response to the original request.
How Does NVMe over Fibre Channel Work? Historically, SANs used three protocols to transfer data: internet small computer systems interface (iSCSI), serial attached SCSI (SAS), and Fibre Channel Protocol (FCP). But the shortcomings of these protocols became apparent when they proved unable to support the full potential of high speed solid state storage. The solution was NVMe, a new storage ...
Fibre Channel vs. SCSI SCSI is a standard interface used for computer-to-storage connectivity, but has limits related to local area network (LAN) storage performance and does not excel at supporting multiple host-to-storage device connections. SCSI is best for point-to-point connections or direct attached storage (DAS) interfacing.
But the reality is that SCSI-based SAS and AHCI-based SATA will be around for several years—although their roles may change. They will be necessary for compatibility with existing servers, storage, I/O devices, hardware, software, systems and deployments, as well as for near-term low-cost high-capacity commodity interfaces.
The term FCP, Fibre Channel Protocol, refers to the interface protocol for SCSI, or the FC-4 mapping. We’re talking about the inner-workings of FC here, not FCP.
SCSI interfaces with external computing components and is usually backwards-compatible. 2. SAS, or Serial Attached SCSI, evolved from SCSI and uses SCSI commands. SAS is a serial communication protocol that enables significantly higher speed data transfers than SCSI’s parallel protocol.
