Editing SCSI (section)

==={{Anchor|SERIAL-VARIANTS}}Modern SCSI===
Recent physical versions of SCSI{{mdashb}}[[Serial Attached SCSI]] (SAS), SCSI-over-[[Fibre Channel Protocol]] (FCP), and [[USB Attached SCSI]] (UAS){{mdashb}}break from the traditional parallel SCSI bus and perform data transfer via serial communications using [[point-to-point (telecommunications)|point-to-point]] links. Although much of the SCSI documentation talks about the parallel interface, all modern development efforts use serial interfaces. Serial interfaces have a number of advantages over parallel SCSI, including higher data rates, simplified cabling, longer reach, improved fault isolation and [[full-duplex]] capability. The primary reason for the shift to serial interfaces is the [[clock skew]] issue of high-speed parallel interfaces, which makes the faster variants of parallel SCSI susceptible to problems caused by cabling and termination.<ref>{{Cite web |url=http://www.infostor.com/index/articles/display/232832/articles/infostor/volume-9/issue-7/features/special-report/the-benefits-of-serial-attached-scsi-sas.html |title=The benefits of Serial Attached SCSI (SAS) |author=David Allen |date=2005-07-01 |access-date=2015-02-06}}</ref>

The non-physical [[iSCSI]] preserves the basic SCSI [[paradigm]], especially the command set, almost unchanged, through embedding of SCSI-3 over [[TCP/IP]]. Therefore, iSCSI uses ''logical connections'' instead of physical links and can run on top of any network supporting IP. The actual physical links are realized on lower [[OSI model|network layers]], independently from iSCSI. Predominantly, [[Ethernet]] is used which is also of serial nature.

SCSI is popular on high-performance workstations, servers, and storage appliances. Almost all RAID subsystems on servers have used some kind of SCSI hard disk drives for decades (initially Parallel SCSI, interim Fibre Channel, recently SAS), though a number of manufacturers offer [[SATA]]-based RAID subsystems as a cheaper option. Moreover, SAS offers compatibility with SATA devices, creating a much broader range of options for RAID subsystems together with the existence of [[nearline SAS]] (NL-SAS) drives. Instead of SCSI, modern desktop computers and notebooks typically use SATA interfaces for internal hard disk drives, with [[NVMe]] over PCIe gaining popularity as SATA can bottleneck modern [[solid-state drive]]s.