|
SCST is a GPL licensed SCSI target software stack. The design goals of this software stack are high performance, high reliability, strict conformance to existing SCSI standards, being easy to extend and easy to use. SCST does not only support multiple SCSI protocols (iSCSI, FC, SRP, ...) but also supports multiple local storage interfaces (SCSI pass-through, block I/O and file I/O) and also storage drivers implemented in user-space via the scst_user driver. In order to reach maximum performance SCST has been implemented as a set of kernel drivers. SCST is often combined with RAID, Deduplication and/or High-availability cluster software to augment its functionality. The SCST software stack is the basis software of many SAN systems. Several world records have been set with SAN systems based on SCST.〔(【引用サイトリンク】 publisher = Fusion-io )〕〔(【引用サイトリンク】 publisher = Fusion-io )〕〔(【引用サイトリンク】 publisher = HP )〕〔(【引用サイトリンク】 publisher = Kaminario )〕 SCST competes with LIO Target for the same purpose of providing a generic SCSI target module inside the Linux kernel.〔https://lwn.net/Articles/424004/〕 For the narrower purpose providing a Linux iSCSI target, the older IET and STGT modules also enjoy industry support.〔Florian Haas, "(Replicate Everything! Highly Available iSCSI Storage with DRBD and Pacemaker )", (Linux iSCSI: a Tale of Four Targets section) ''Linux Journal'' Issue #217, May 2012〕 SCST is now primarily developed by SanDisk personnel, after Fusion-io acquired in 2013 the start-up ID7 which initially developed SCST〔(【引用サイトリンク】url=http://www.fusionio.com/id7 )〕 and after SanDisk acquired Fusion-io in 2014. == Architecture == SCST consists of three groups of modules: * The SCST core, a protocol-independent engine for processing SCSI commands. * Target drivers which receive SCSI commands from a SCSI initiator, pass these SCSI to the SCST core and send back replies to the initiator. * Storage drivers a.k.a. device handlers which interact with the storage medium. The supported local storage interfaces are SCSI, block device, file and scst_user. scst_user is an SCST-specific protocol that allows efficient implementation of storage drivers in user space. Configuration of all these modules happens via a Sysfs interface. Although direct configuration of SCST via its Sysfs interface is convenient, the tool called scstadmin allows to control SCST via its sysfs interface and also to save and restore the SCST configuration. The following design aspects help SCST to reach the high performance this project is known for: * The number of threads per storage device that processes SCSI commands is configurable. * All target driver and storage driver functions invoked by the SCST core are asynchronous, at least when the Linux kernel allows this. It is e.g. not yet possible to perform asynchronous or direct I/O from inside the Linux kernel. * One Finite-state machine is associated with each SCSI command. This allows a single command thread to process multiple SCSI commands concurrently. * Even when using multiple threads per storage device all these threads share the same I/O scheduler. This sharing improves performance significantly when using e.g. the CFQ I/O scheduler. * A scatter-gather vector cache. This cache avoids having to allocate memory via the kernel for each SCSI command. * Lockless access to certain data structures needed to process SCSI commands. This also means that I/O has to be suspended before any of the data structures that are accessed without locking can be modified. * SCSI commands can be submitted by a target driver to the SCST core from softirq context. This results in a lower number of context switches compared to having to submit SCSI commands from thread context. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「SCST」の詳細全文を読む スポンサード リンク
|