mirror of
https://github.com/SCST-project/scst.git
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Vladislav Bolkhovitin
5d4789c8c0
git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@163 d57e44dd-8a1f-0410-8b47-8ef2f437770f
433 lines
20 KiB
HTML
433 lines
20 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<html>
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<head>
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<meta http-equiv="content-type"
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content="text/html; charset=ISO-8859-1">
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<title>SCST: Generic SCSI Target Middle Level for Linux</title>
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<meta name="Keywords"
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content="SCST, Linux, SCSI target, Qlogic, QLA2200, QLA2300, iSCSI, SCSI">
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</head>
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<body>
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<a href="http://sourceforge.net"> <img
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src="http://sourceforge.net/sflogo.php?group_id=110471&type=5"
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alt="SourceForge.net Logo" border="0" height="62" width="210"></a>
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<h1><small>Generic SCSI Target Middle Level for Linux</small><br>
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</h1>
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<p style="text-align: justify;">The SCSI target mid-level subsystem for
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Linux (SCST) is a subsystem of the Linux kernel that provides a
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standard framework for SCSI target drivers development. It is designed
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to
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provide unified, consistent interface between SCSI target drivers and
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Linux kernel and simplify target drivers development as much as
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possible. A system with a SCSI target device is able to share its local
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or virtual devices with other systems on a network with SCSI protocol
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support, e.g. SCSI bus, Fibre Channel, TCP/IP with iSCSI. This is
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commonly used for data storage virtualization.<br>
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</p>
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<p style="text-align: justify;">SCST has the following features:</p>
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<div style="text-align: justify;">
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</div>
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<p style="text-align: justify;">
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</p>
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<div style="text-align: justify;">
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</div>
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<ul style="text-align: justify;">
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<li>Simple, easy to use interface with target drivers. Particularly,
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SCST performs all required pre- and post- processing of incoming
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requests and all necessary error recovery.</li>
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<li>Undertakes most problems, related to execution contexts, thus
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practically eliminating one of the most complicated problem in the
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kernel drivers development. For example, a target driver for QLogic
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2200/2300 cards, which has all necessary features, is only ~2000 lines
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of code long.</li>
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<li> Very low overhead, fine-grained locks and simplest commands
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processing path, which allow to reach maximum possible performance and
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scalability. Particularly, incoming
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requests can be processed in the caller's context or in
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one of the internal SCST's tasklets, therefore no extra context
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switches
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required.</li>
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<li>Provides advanced per-initiator device visibility management (LUN
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masking),
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which allows different initiators see different set of devices
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with different access permissions. For instance, initiator A could see
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exported from
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target T devices Da and Db read-writable, and initiator B from the same
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target T could see devices Db read-only and Dc read-writable.<br>
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</li>
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<li> Emulates necessary functionality of SCSI host adapter, because
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from remote initiators point of view SCST acts as a SCSI host with
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its
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own devices. This is especially important in pass-through mode with one
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to many relationship, i.e. when
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multiple initiators can connect to the exported pass-through devices.
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You can find more deep elaboration why it is needed in <a
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href="http://www.mail-archive.com/linux-scsi@vger.kernel.org/msg06911.html">this</a>
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message in linux-scsi mailing list. Some of the emulated functions are
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the following:
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<ul>
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<li> Generation of necessary UNIT ATTENTIONs, their storage and
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delivery to all connected remote initiators. </li>
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<li> RESERVE/RELEASE functionality. </li>
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<li> CA/ACA conditions (not implemented yet). </li>
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<li> All types of RESETs and other task management functions. </li>
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<li> REPORT LUNS command as well as SCSI address space management
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in order to have consistent address space on all remote initiators,
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since local SCSI devices could not know about each other to report
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via REPORT LUNS command. Additionally, SCST responds with error on
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all commands to non-existing devices and provides access control, so
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different remote initiators could see
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different set of devices. </li>
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<li> Other necessary functionality (task attributes, etc.) as
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specified in SAM-2, SPC-2, SAM-3, SPC-3 and other SCSI standards. </li>
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</ul>
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</li>
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<li> Device handlers (i.e. plugins) architecture provides extra
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flexibility by allowing to make any additional
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requests processing, which is completely independent from target
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drivers and SCST core, like, for instance, device dependent exceptional
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conditions treatment, data caching or passing commands in the user
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space for device emulation. Example of such plugin is FILEIO device
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handler (see below) .<br>
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</li>
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<li> Complete SMP support.<br>
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</li>
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<li>Well documented.<br>
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</li>
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</ul>
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<div style="text-align: justify;">
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</div>
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<p style="text-align: justify;">Interoperability between SCST and local
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SCSI initiators (i.e. sd, st, etc.) is
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the additional issue that SCST is going to address (it is not
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implemented yet). It is necessary, because local SCSI initiators can
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change the state of the device, for example RESERVE the device, or some
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of its parameters and that could be done behind SCST, which could lead
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to various problems, including data corruption. Thus, RESERVE/RELEASE
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commands, locally generated
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UNIT ATTENTIONs, etc. should be intercepted and processed as if local
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SCSI initiators act as remote SCSI initiators connected to SCST.<br>
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</p>
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<p style="text-align: justify;">Interface between SCST and target
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drivers is based on work, done by <a href="http://www.iol.unh.edu/">University
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of New Hampshire Interoperability Labs (UNH IOL)</a> for the <a
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href="http://www.iol.unh.edu/consortiums/iscsi/index.html">UNH-iSCSI
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project</a>, which is currently developed on <a
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href="http://unh-iscsi.sourceforge.net/">SourceForge.net</a>.<br>
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</p>
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<p style="text-align: justify;">SCST supports the following I/O modes:<br>
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</p>
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<ul>
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<li>Pass-through mode with one to many relationship, i.e. when
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multiple initiators can connect to the exported pass-through devices,
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for virtually all SCSI devices types: disks
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(type 0), tapes (type 1), processors (type
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3), CDROMs (type 5), MO disks (type 7), medium changers (type 8) and
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RAID controllers (type 0xC)</li>
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<li>FILEIO mode, which allows to use files on file
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systems or block devices as virtual remotely available SCSI disks or
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CDROMs with benefits of the Linux page cache<br>
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</li>
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<li>BLOCKIO mode, which performs direct block IO with a block device,
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bypassing page-cache for all operations. This mode works ideally with
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high-end storage HBAs and for applications that either do not need
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caching between application and disk or need the large block throughput.</li>
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<li>User space mode using scst_user device handler, which allows to
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implement in the user space virtual SCSI devices in the SCST environment<br>
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</li>
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<li>"Performance" device handlers, which provide in pseudo
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pass-through mode a way for direct
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performance measurements without overhead of actual data transferring
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from/to underlying SCSI device<br>
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</li>
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</ul>
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<p style="text-align: justify;">The latest stable version is 0.9.5.
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Requires Linux kernel 2.6.14 or higher.
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Tested mostly on i386 and x86_64,
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but should also
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work on any other
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supported by Linux platform. More detail information you could find in
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the project's README file.
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</p>
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Starting from version 0.9.4 2.4 Linux
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kernels are not supported anymore. The latest
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stable
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version of SCST for 2.4 kernels is 0.9.3.1-24.
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<p style="text-align: justify;">If you have any questions you can ask
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them on the SCST SF.net page either using forum, or scst-devel mailing
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list.<br>
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</p>
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<a href="http://sourceforge.net/project/showfiles.php?group_id=110471">Download</a><br>
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<a href="http://www.sourceforge.net/projects/scst">SCST SF.net project
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page</a><br>
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<a href="ChangeLog.scst">Change Log</a><br>
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Documentation: <a href="doc/scst_pg.html">HTML</a>, <a
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href="doc/scst_pg.pdf">PDF</a>, <a href="doc/scst_user_spec.txt">scst_user
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interface description</a><br>
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Some nice SCST call graphs, created by Ming Zhang: <a
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href="doc/init_scst.png">init_scst</a>, <a
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href="doc/scst_cmd_thread.png">scst_cmd_thread</a>, <a
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href="doc/scst_mgmt_cmd_thread.png">scst_mgmt_cmd_thread</a>, <a
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href="doc/scst_mgmt_thread.png">scst_mgmt_thread</a><br>
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<p>The latest development version of SCST and target drivers is
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available directly from the
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project's SVN. The SCST release policy is to make stable releases
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twice a year, with the only exception if the current stable version
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contains a critical bug. Therefore on practice the development version
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in the SVN
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is usually more stable, than the "stable" one. You can access it using
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either <a href="http://svn.sourceforge.net/scst">web-based SVN
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repository viewer</a> or using anonymous access: </p>
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<p> <tt> svn co https://scst.svn.sourceforge.net/svnroot/scst<br>
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</tt></p>
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<p>More information about accessing SVN repository may be found <a
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href="http://sourceforge.net/docs/E09">here</a>.<br>
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</p>
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<p>History of the pre-SVN SCST development is available in SCST CVS
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repository, which is accessible using <a
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href="http://cvs.sourceforge.net/viewcvs.py/scst">web-based CVS
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repository viewer</a> or anonymous CVS access.<br>
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</p>
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<hr
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style="width: 100%; height: 2px; margin-left: 0px; margin-right: 0px;">
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<h1><small>SCST administration utility<br>
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</small></h1>
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<p>SCST administration utility "scstadmin" is developed by Mark
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Buechler. With it you can manually or automatically using either plain
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text config file, or MySQL database configure every aspect of SCST, for
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instance as part of the system startup/shutdown, including
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enabling/disabling target mode on your target SCSI controller.<br>
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</p>
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<p><a
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href="http://sourceforge.net/project/showfiles.php?group_id=110471">Download</a>
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</p>
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<hr
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style="width: 100%; height: 2px; margin-left: 0px; margin-right: 0px;">
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<h1><small>ISCSI target driver iSCSI-SCST<br>
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</small></h1>
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<div style="text-align: justify;">
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<p>ISCSI-SCST is a forked (with all respects) version of <a
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href="http://iscsitarget.sourceforge.net/">IET</a> with
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updates to work over SCST as well as with many improvements and
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bugfixes. The reason of fork is that the necessary changes are
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intrusive and with the current IET merge policy, where only simple
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bugfix-like patches, which doesn't touch the core code, could be
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merged, it is very unlikely that they will be merged in the main IET
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trunk.<br>
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</p>
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<p>ISCSI-SCST has the following major advantages over the mainline IET:<br>
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</p>
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<ul>
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<li>It uses full SCST power without loosing any existing feature
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(except, maybe, "illegal" from SCSI specifications point of view MPIO).
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Namely, you can use with it:</li>
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</ul>
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<ul style="list-style-type: circle; margin-left: 40px;">
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<li>Pass-through mode with one to many relationship, i.e. when
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multiple initiators can connect to the exported pass-through devices
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(see above). For instance, you can safely export your parallel SCSI
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tape or tape library on your iSCSI net and multiple initiators can
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share it without risk of data loss because of the shared usage.
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Existing "rawio" patch for IET supports only non-enforced 1:1
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relationship, so it is unsafe to use it in multiple initiators
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environments.<br>
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</li>
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<li>More advances devices visibility management, when different
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initiators can see different set of devices with different access
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permissions from the same target.</li>
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<li>O_DIRECT, i.e. "BLOCKIO on files", mode, which has all advantages
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of BLOCKIO, but also supports files on file systems. Sometimes, in the
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appropriate cases, this mode can make performance difference in 100% or
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even more.</li>
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<li>With 4KB blocks you can forget about abysmal write performance
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caused by misaligned partitions. All modern OS'es, including Windows
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starting from, at least, Windows 2000, work perfectly with 4KB block
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devices without any additional storage or handling overhead.</li>
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<li>Virtual CD/DVD-ROMs without necessity for manual patching.</li>
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<li>Ability to create target devices emulators in the user space.</li>
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<li>Ability to create multi-transport SCSI targets, which can export
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(possibly, the same) devices over multiple transports.</li>
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</ul>
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<ul>
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<li>It has many code improvements and cleanups, including stability
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and iSCSI RFC violations fixes. If you are an IET user and consider IET
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problemless, I'm sorry for the bad news. IET works well only on "fast"
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paths and regularly used branches, in many other less used cases IET
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has various problems, from simply ignoring error processing, as it is
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with memory allocations, to crashing itself with BUG() macro, as it is
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for malformed packets from initiators. ChangeLog file lists most
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noticeable fixes, but there were a lot of many other smaller ones.</li>
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</ul>
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<ul>
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<li>Due to its reworked IO architecture and SCST backend iSCSI-SCST
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has better performance in many cases. In future with upcoming SCST
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improvements, like zero-copy with Linux cache FILEIO, the performance
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difference is going to be even bigger. Currently in tests from a single
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initiator over a single connection on 1GbE hardware over FILEIO vdisk
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iSCSI-SCST with default settings usually outperforms tuned IET a on
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3-10% (by default IET has not too good settings, so it shows
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considerably worse results) or has the similar performance. The bigger
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difference is expected with 10GbE hardware or with higher number of
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initiators, since iSCSI-SCST has less commands processing overhead per
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command, hence put less load on CPU. If you find a case where
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iSCSI-SCST has worse performance, than IET, please report it to SCST
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mailing list scst-devel@lists.sourceforge.net, it will be greatly
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appreciated.</li>
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</ul>
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<p>Also, in contrast to IET, iSCSI-SCST is open for any new
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development, modifications and improvements, so people who want to fix
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or implement something new will not have to keep and maintain separate
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patches as it is currently necessary with IET. ISCSI-SCST is going to
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be actively developed and gain in the future new features like support
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for multiple connections per session, error recovery levels >0,
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etc., which eventually make it really "enterprise".<br>
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</p>
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<p>ISCSI-SCST is available for download from the <a
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href="http://svn.sourceforge.net/scst">SCST SVN repository</a>. See
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above how to setup access to it.<br>
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</p>
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<p>After some testing for month-two, iSCSI-SCST is going to be fully
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released.<br>
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</p>
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<p>If you are an IET user, please, before installation carefully read
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README files of both iSCSI-SCST and the SCST core. Especially pay
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attention that now the LUN information for iSCSI-SCST is configured not
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using iscsi-scstd.conf file in /etc, but using corresponding SCST
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facilities. This is because now the responsibilities are divided (as it
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should be) between the target driver (iSCSI-SCST) and the SCST core.
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The target driver is responsible for handling targets and their
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parameters, SCST core is responsible for handling backstorage.<br>
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</p>
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</div>
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<hr
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style="width: 100%; height: 2px; margin-left: 0px; margin-right: 0px;">
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<h1><small>Target driver for QLogic 2200/2300 cards<br>
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</small></h1>
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<div style="text-align: justify;">
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<p>This is ported and improved version of the "old" target driver for
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2.4 kernels (see below) to the in-tree 2.6 QLogic 2x00 initiator
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driver. The port was done by Nathaniel Clark. This is stable and
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functional driver with
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the larger feature set, than the parent driver has.</p>
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<p style="text-align: justify;">The latest version is 0.9.5. Requires
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Linux kernel version 2.6.16.x or higher and SCST version 0.9.5 or
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higher.
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Tested mostly on i386 and
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x86_64, but
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should work on any other supported by Linux platform.
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</p>
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<p style="text-align: justify;">You can find the latest development
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version of this driver in the SCST SVN. See above how to setup access
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to it.<br>
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</p>
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<p style="text-align: justify;"><a
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href="http://sourceforge.net/project/showfiles.php?group_id=110471">Download</a><br>
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<a href="ChangeLog.qla26">Change Log</a><br>
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</p>
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</div>
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<hr style="width: 100%; height: 2px;">
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<h1><small>Target driver for LSI/MPT cards</small></h1>
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Target driver LSI/MPT cards was originally developed by Hu Gang, then
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Erik Habbinga has continued the development. This driver is on the
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alpha stage and available for download from the <a
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href="http://svn.sourceforge.net/scst">SCST SVN repository</a>. See
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above how to setup access to it.<br>
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<br>
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<hr style="width: 100%; height: 2px;">
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<h1><small>SCSI RDMA Protocol (SRP) Target driver</small></h1>
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SCSI RDMA Protocol (SRP) Target driver is developed
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independently from SCST team. You can find instructions how to download
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and install it on this page: <a
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href="http://lists.openfabrics.org/pipermail/iwg/2007-March/000378.html">http://lists.openfabrics.org/pipermail/iwg/2007-March/000378.html</a><br>
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<br>
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<hr style="width: 100%; height: 2px;">
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<h1><small>Target driver for QLogic ISP chipsets<br>
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</small></h1>
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This is target driver for ISP QLogic chipsets commonly used in many
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SCSI and FC host bus adapters. Supported chipsets are listed in README
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file, incomplete list of supported HBA's is in doc/Hardware.txt. It is
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based on Matthew Jacob's multiplatform driver for ISP chipsets, which
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can be downloaded from <a
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href="ftp://ftp.feral.com/pub/isp/isp_dist.tgz">ftp://ftp.feral.com/pub/isp/isp_dist.tgz</a>.
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The update for SCST was made and supported by Stanislaw Gruszka.<br>
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<br>
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One major difference of this driver from the above target driver for
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QLogic 2200/2300 cards is that it supports 24xx series of chipsets.<br>
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<br>
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This driver is unstable and on the
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alpha stage. It is available for download from the <a
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href="http://svn.sourceforge.net/scst">SCST SVN repository</a>. See
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above how to setup access to it.<br>
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<br>
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<hr style="width: 100%; height: 2px;">
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<h1><small>Old target driver for QLogic 2200/2300 cards for 2.4 kernels<br>
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</small></h1>
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<div style="text-align: justify;">Old target driver for QLogic
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2200/2300
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cards is capable to work on 2.4 kernels. It has all required features
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and
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looks to be quite stable. It is designed to work in conjunction with
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the initiator
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driver, which is intended to perform all the initialization and
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shutdown tasks. In the current release as a base for the initiator
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driver was taken Red Hat's driver from the stock 2.4.20 kernel. Then it
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was patched to enable the target mode and provide all
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necessary callbacks, and it's still able to work as initiator only.
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Mode, when a host acts as the initiator and the target simultaneously,
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is also supported. This driver is obsoleted in favor of
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2.6-based driver (see above).<br>
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<br>
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The latest version is 0.9.3.4. Requires Linux kernel versions 2.4.20 or
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higher and SCST version 0.9.3-pre4 or higher. If you are lucky, it
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works also on 2.6 kernels, see README file
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for details. Tested on i386 only, but
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should work on any other supported by Linux platform.<br>
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<br>
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Currently it is not supported and listed here for historical reasons
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only.<br>
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<br>
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</div>
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<a href="http://sourceforge.net/project/showfiles.php?group_id=110471">Download</a><br>
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|
<a href="ChangeLog.qla">Change Log</a>
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|
<hr style="width: 100%; height: 2px;"><span style="font-weight: bold;"></span>
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<h1><small>Target drivers for Adaptec 7xxx and QLogic QLA12xx
|
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cards</small></h1>
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|
Target drivers for Adaptec 7xxx and QLogic QLA12xx cards have
|
|
been developed by Hu Gang and they available for download from <a
|
|
href="http://bj.soulinfo.com/%7Ehugang/scst/tgt/">http://bj.soulinfo.com/~hugang/scst/tgt/</a>.
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|
These drivers are not completed, but looks to be a good starting point
|
|
if you are going to use one of these cards.
|
|
SCST team don't have the appropriate hardware, therefore have not
|
|
tested and don't support these drivers. Send all questions to Hu Gang
|
|
<hugang
|
|
% soulinfo.com>. If some of these drivers don't compile for you, try
|
|
again with SCST version 0.9.3-pre2.<br>
|
|
<br>
|
|
<a href="http://bj.soulinfo.com/%7Ehugang/scst/tgt/">Download</a><br>
|
|
<br>
|
|
<hr style="width: 100%; height: 2px;">
|
|
<h1><small>Patches for UNH-iSCSI Target 1.5.03 and 1.6.00 to work over
|
|
SCST</small></h1>
|
|
SCST is much more advanced, than the internal mid-level of <a
|
|
href="http://sourceforge.net/projects/unh-iscsi">UNH-iSCSI target
|
|
driver</a>.
|
|
With SCST the iSCSI target benefits from all its features and gets
|
|
ability to use all its advantages, like high performance and
|
|
scalability, SMP support, required SCSI functionality emulation, etc.<br>
|
|
<br>
|
|
Since the interface between SCST and the target drivers is based on
|
|
work, done by UNH IOL, it was relatively simple to update UNH-iSCSI
|
|
target to work over SCST. Mostly it was "search and replace" job. The
|
|
built-in scsi_target remains available as a compile-time option.<br>
|
|
<br>
|
|
Requires Linux kernel versions 2.4.20 or
|
|
higher or 2.6.7 or higher and SCST version 0.9.2 or higher.<br>
|
|
<br>
|
|
Currently it is not supported and listed here for historical reasons
|
|
only.<br>
|
|
<br>
|
|
<a href="http://sourceforge.net/project/showfiles.php?group_id=110471">Download</a><br>
|
|
<br>
|
|
</body>
|
|
</html>
|