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Yan Burman 799ddae085 Merged revisions 5322-5326,5329-5340,5344-5371,5382-5407 via svnmerge from 
svn+ssh://yanb123@svn.code.sf.net/p/scst/svn/trunk

........
  r5322 | vlnb | 2014-03-05 05:27:21 +0200 (Wed, 05 Mar 2014) | 13 lines
  
  scst_vdisk: Make vdisk_nullio size configurable
  
  Keep the default size of vdisk_nullio devices at VDISK_NULLIO_SIZE. Add
  a sysfs attribute 'size' which is the size of a vdisk device in
  bytes. Make the size of vdisk_nullio devices configurable. Accept
  "size" and "size_mb" as creation parameters for vdisk_nullio
  devices. Generate a CAPACITY DATA HAS CHANGED unit attention after size
  changes. Refuse any attempt to change the size into a number that is
  not a multiple of the block size.
  
  Signed-off-by: Bart Van Assche <bvanassche@acm.org>
........
  r5323 | bvassche | 2014-03-06 09:29:00 +0200 (Thu, 06 Mar 2014) | 1 line
  
  scst_vdisk: Avoid that smatch complains about unreachable code
........
  r5324 | vlnb | 2014-03-07 06:02:39 +0200 (Fri, 07 Mar 2014) | 27 lines
  
  PERSISTENT RESERVE IN: Suppress a kernel warning for small output buffer sizes
  
  This patch suppresses the following error message and kernel warning:
  
  scst: ***ERROR***: Too big response data len 24 (max 8), limiting it to the max (dev iis)
  Call Trace:
   [<ffffffff818b1193>] ? dump_stack+0x41/0x56
   [<ffffffffa01c1a8f>] ? scst_set_resp_data_len+0x82/0xb1 [scst]
   [<ffffffffa01ca80f>] ? scst_pr_read_reservation+0xbf/0xc4 [scst]
   [<ffffffffa01b707b>] ? scst_persistent_reserve_in_local+0x140/0x1ce [scst]
   [<ffffffffa01b7cee>] ? scst_exec_check_blocking+0x57/0xf1 [scst]
   [<ffffffffa01b85f4>] ? scst_process_active_cmd+0x86c/0x136f [scst]
   [<ffffffffa01b913c>] ? scst_do_job_active+0x45/0x5b [scst]
   [<ffffffffa01b939c>] ? scst_cmd_thread+0x218/0x2b7 [scst]
   [<ffffffff8105292a>] ? wake_up_bit+0x23/0x23
   [<ffffffffa01b9184>] ? scst_cmd_tasklet+0x32/0x32 [scst]
   [<ffffffff81052355>] ? kthread_freezable_should_stop+0x51/0x51
   [<ffffffffa01b9184>] ? scst_cmd_tasklet+0x32/0x32 [scst]
   [<ffffffff81052400>] ? kthread+0xab/0xb3
   [<ffffffff81052355>] ? kthread_freezable_should_stop+0x51/0x51
   [<ffffffff818b4e3c>] ? ret_from_fork+0x7c/0xb0
   [<ffffffff81052355>] ? kthread_freezable_should_stop+0x51/0x51
  
  Reported-by: Roman Bogdanov <bogdanovr@gmail.com>
  Signed-off-by: Bart Van Assche <bvanassche@acm.org>
........
  r5325 | bvassche | 2014-03-08 15:30:29 +0200 (Sat, 08 Mar 2014) | 1 line
  
  nightly build: Update kernel versions
........
  r5326 | vlnb | 2014-03-13 05:50:37 +0200 (Thu, 13 Mar 2014) | 3 lines
  
  Update link to Gentoo HOWTO from Jurie Botha
........
  r5329 | vlnb | 2014-03-15 03:38:06 +0200 (Sat, 15 Mar 2014) | 3 lines
  
  Cleanup
........
  r5330 | vlnb | 2014-03-15 03:38:37 +0200 (Sat, 15 Mar 2014) | 3 lines
  
  Implement REPORT SUPPORTED TASK MANAGEMENT FUNCTIONS command
........
  r5331 | vlnb | 2014-03-15 03:40:57 +0200 (Sat, 15 Mar 2014) | 8 lines
  
  scst_vdisk: Remove an unused parameter from vdisk_fsync*()
  
  The "struct vdisk_cmd_params *p" parameter is neither used by vdisk_fsync(),
  vdisk_fsync_blockio() nor by vdisk_fsync_fileio() so remove it.
  
  Signed-off-by: Bart Van Assche <bvanassche@acm.org>
........
  r5332 | vlnb | 2014-03-15 03:42:06 +0200 (Sat, 15 Mar 2014) | 8 lines
  
  vdisk_blockio: Change default vendor name back to "SCST_BIO"
  
  In r5316 the default vendor name for vdisk_blockio devices was changed
  into "SCST_FIO". Change this back into "SCST_BIO".
  
  Signed-off-by: Bart Van Assche <bvanassche@acm.org>
........
  r5333 | vlnb | 2014-03-15 03:44:35 +0200 (Sat, 15 Mar 2014) | 8 lines
  
  vdisk_blockio: Add VERIFY implementation
  
  There is already an implementation of the VERIFY command for vdisk_fileio
  devices. Add an implementation for vdisk_blockio devices.
  
  Signed-off-by: Bart Van Assche <bvanassche@acm.org>
........
  r5334 | vlnb | 2014-03-15 04:01:17 +0200 (Sat, 15 Mar 2014) | 8 lines
  
  scst_vdisk: Implement COMPARE AND WRITE
  
  Ensure that COMPARE AND WRITE is executed atomically by serializing
  all COMPARE AND WRITE commands per device (SCST_SERIALIZED).
  
  Signed-off-by: Bart Van Assche <bvanassche@acm.org>
........
  r5335 | vlnb | 2014-03-15 04:09:17 +0200 (Sat, 15 Mar 2014) | 5 lines
  
  Fix URL to SCST website
  
  Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
........
  r5336 | vlnb | 2014-03-15 04:13:58 +0200 (Sat, 15 Mar 2014) | 3 lines
  
  Cleanup
........
  r5337 | bvassche | 2014-03-15 08:47:26 +0200 (Sat, 15 Mar 2014) | 1 line
  
  scripts/kernel-functions: Kernel 3.13.6 build fix
........
  r5338 | bvassche | 2014-03-16 15:38:50 +0200 (Sun, 16 Mar 2014) | 1 line
  
  srpt: Minor buid process terminology change
........
  r5339 | bvassche | 2014-03-18 17:35:13 +0200 (Tue, 18 Mar 2014) | 1 line
  
  ib_srpt: Avoid that session logout hangs sporadically
........
  r5340 | vlnb | 2014-03-19 06:28:46 +0200 (Wed, 19 Mar 2014) | 8 lines
  
  scst/README: Show how to read SCST sysfs attributes
  
  Make the behavior of SCST sysfs attributes more clear by adding
  examples in scst/README of code for reading and writing these attributes.
  
  Signed-off-by: Bart Van Assche <bvanassche@acm.org>
........
  r5344 | bvassche | 2014-03-20 17:13:50 +0200 (Thu, 20 Mar 2014) | 1 line
  
  ib_srpt: Simplify srpt_handle_cmd()
........
  r5345 | bvassche | 2014-03-20 17:14:45 +0200 (Thu, 20 Mar 2014) | 5 lines
  
  ib_srpt: Micro-optimize I/O context state manipulation
      
  All ioctx->state manipulations are serialized per command so it is
  not necessary to use locking to protect these manipulations.
........
  r5346 | bvassche | 2014-03-20 17:15:54 +0200 (Thu, 20 Mar 2014) | 8 lines
  
  ib_srpt: Handle GID change events properly
      
  The mlx4_core driver generates a GID change event after a port has been
  changed from IB into Ethernet mode. Avoid that this causes the following
  error message to appear in the system log:
      
  ib_srpt: ***ERROR***: received unrecognized IB event 18
........
  r5347 | bvassche | 2014-03-20 17:16:27 +0200 (Thu, 20 Mar 2014) | 1 line
  
  ib_srpt/Makefile: Add kerneldoc target
........
  r5348 | bvassche | 2014-03-20 17:17:04 +0200 (Thu, 20 Mar 2014) | 1 line
  
  ib_srpt: Fix an error reported by the kerneldoc tool
........
  r5349 | bvassche | 2014-03-20 17:18:06 +0200 (Thu, 20 Mar 2014) | 5 lines
  
  ib_srpt: Avoid that cmd_wait_list processing triggers command reordering
  
  Although harmless for SCSI commands with SIMPLE ordering, avoid that commands
  received before RTU can get reordered.
........
  r5350 | bvassche | 2014-03-20 17:18:38 +0200 (Thu, 20 Mar 2014) | 2 lines
  
  ib_srpt: Micro-optimize SRP_CMD parsing
........
  r5351 | bvassche | 2014-03-20 17:19:05 +0200 (Thu, 20 Mar 2014) | 1 line
  
  ib_srpt: Sync information unit memory only once
........
  r5352 | bvassche | 2014-03-20 17:19:34 +0200 (Thu, 20 Mar 2014) | 2 lines
  
  ib_srpt: Introduce a temporary variable in srpt_handle_new_iu()
........
  r5353 | bvassche | 2014-03-20 17:20:55 +0200 (Thu, 20 Mar 2014) | 2 lines
  
  ib_srpt: Micro-optimize polling
........
  r5354 | bvassche | 2014-03-20 17:22:19 +0200 (Thu, 20 Mar 2014) | 5 lines
  
  ib_srpt: Rework multi-channel support
  
  Store initiator and target port ID's once per nexus instead of in each
  channel data structure.
........
  r5355 | bvassche | 2014-03-20 17:23:16 +0200 (Thu, 20 Mar 2014) | 2 lines
  
  ib_srpt: Simplify channel state management code
........
  r5356 | bvassche | 2014-03-20 17:24:18 +0200 (Thu, 20 Mar 2014) | 5 lines
  
  ib_srpt: Defer destroying the QP until the TimeWait state has been left
  
  This is necessary to avoid that a login gets rejected due to reusing a
  queue pair number that has not yet been freed by the target side.
........
  r5357 | bvassche | 2014-03-20 17:25:34 +0200 (Thu, 20 Mar 2014) | 5 lines
  
  ib_srpt: Rework waiting for last WQE
  
  After having changed the queue pair state into "error", queue an additional
  work request instead of waiting for the last WQE event.
........
  r5358 | bvassche | 2014-03-20 17:26:48 +0200 (Thu, 20 Mar 2014) | 1 line
  
  srpt/session-management.txt: Document how sessions are managed by the ib_srpt driver
........
  r5359 | bvassche | 2014-03-20 18:10:19 +0200 (Thu, 20 Mar 2014) | 1 line
  
  scst_const.h: Make COMPARE_AND_WRITE definition available for kernel versions 3.6..3.11
........
  r5360 | vlnb | 2014-03-21 03:58:13 +0200 (Fri, 21 Mar 2014) | 3 lines
  
  In VERIFY commands BYTCHK 1x is not supported (yet)
........
  r5361 | bvassche | 2014-03-21 18:29:26 +0200 (Fri, 21 Mar 2014) | 1 line
  
  srpt/Makefile: Avoid that the build process depends on source control tools
........
  r5362 | vlnb | 2014-03-22 01:12:42 +0200 (Sat, 22 Mar 2014) | 3 lines
  
  Fix error recovery of internal commands
........
  r5363 | bvassche | 2014-03-24 13:53:00 +0200 (Mon, 24 Mar 2014) | 1 line
  
  ib_srpt: Clarify a kernel-doc comment
........
  r5364 | bvassche | 2014-03-24 13:55:56 +0200 (Mon, 24 Mar 2014) | 1 line
  
  ib_srpt: Add newline at the end of kernel warning statements
........
  r5365 | bvassche | 2014-03-24 13:57:39 +0200 (Mon, 24 Mar 2014) | 5 lines
  
  ib_srpt: Change the severity level of a log message
  
  Make sure that target port state changes get logged even with
  debugging disabled.
........
  r5366 | bvassche | 2014-03-24 13:59:27 +0200 (Mon, 24 Mar 2014) | 5 lines
  
  ib_srpt: Clean up srpt_destroy_ch_ib()
  
  All callers guarantee that the completion queue is empty so it is
  not necessary to invoke ib_poll_cq() from inside this function.
........
  r5367 | bvassche | 2014-03-24 14:01:07 +0200 (Mon, 24 Mar 2014) | 5 lines
  
  ib_srpt: Micro-optimize srpt_adjust_srq_wr_avail()
  
  The overhead of atomic_add_return() is lower than that of a
  spin_lock() / spin_unlock() pair, hence switch to the former.
........
  r5368 | bvassche | 2014-03-24 14:03:09 +0200 (Mon, 24 Mar 2014) | 20 lines
  
  ib_srpt: Fix a kernel warning
  
  Avoid that the following (very rare) kernel warning is reported
  when an ib_srpt target port is disabled while I/O is ongoing:
  
  WARNING: CPU: 3 PID: 12259 at srpt/src/ib_srpt.c:3334 srpt_xmit_response+0x165/0x300 [ib_srpt]()
  Unexpected command state 6
  Call Trace:
   [<ffffffff814a15dc>] dump_stack+0x4e/0x7a
   [<ffffffff8104bc5d>] warn_slowpath_common+0x7d/0xa0
   [<ffffffff8104bccc>] warn_slowpath_fmt+0x4c/0x50
   [<ffffffffa0771525>] srpt_xmit_response+0x165/0x300 [ib_srpt]
   [<ffffffffa082aacc>] scst_xmit_response+0xbc/0x560 [scst]
   [<ffffffffa083123d>] scst_process_active_cmd+0x29d/0x7b0 [scst]
   [<ffffffffa0832bd9>] scst_do_job_active+0x89/0x1a0 [scst]
   [<ffffffffa0832e4f>] scst_cmd_thread+0x15f/0x350 [scst]
   [<ffffffff810766cd>] kthread+0xed/0x110
   [<ffffffff814b312c>] ret_from_fork+0x7c/0xb0
  ---[ end trace 591f7af7d006fc0e ]---
........
  r5369 | bvassche | 2014-03-24 14:04:44 +0200 (Mon, 24 Mar 2014) | 5 lines
  
  ib_srpt: Add a kernel warning
  
  Invoking srpt_zerolength_write() before the queue pair has reached
  the error state is a bug, so complain loudly if that happens.
........
  r5370 | bvassche | 2014-03-24 14:07:43 +0200 (Mon, 24 Mar 2014) | 7 lines
  
  ib_srpt: Avoid waiting for missing error completions
  
  Apparently with mlx4 firmware up to and including 2.30.8000 it is not
  guaranteed that for a QP associated with an SRQ error completions are
  generated for all pending work requests. Avoid triggering
  srpt_pending_cmd_timeout() for missing error completions.
........
  r5371 | bvassche | 2014-03-25 18:19:00 +0200 (Tue, 25 Mar 2014) | 1 line
  
  nightly build: Update kernel versions
........
  r5382 | vlnb | 2014-03-26 04:31:52 +0200 (Wed, 26 Mar 2014) | 6 lines
  
  Black hole functionality added
  
  Scst_mutex intentially used directly in the sysfs handler, because
  comming sysfs improvements will allow that.
........
  r5383 | vlnb | 2014-03-26 05:18:03 +0200 (Wed, 26 Mar 2014) | 5 lines
  
  documentation: Document SCST_SERIALIZED and SCST_STRICTLY_SERIALIZED
  
  Signed-off-by: Bart Van Assche <bvanassche@acm.org>
........
  r5384 | vlnb | 2014-03-26 05:18:36 +0200 (Wed, 26 Mar 2014) | 3 lines
  
  Cleanup
........
  r5385 | vlnb | 2014-03-26 05:20:04 +0200 (Wed, 26 Mar 2014) | 9 lines
  
  scst_local: Remove two superfluous tests
  
  The to_scst_lcl_sess() macro is based on container_of() and hence never
  returns NULL. Hence remove the two tests that compare the result of that
  macro against NULL.
  
  Signed-off-by: Bart Van Assche <bvanassche@acm.org>
........
  r5386 | vlnb | 2014-03-26 05:21:25 +0200 (Wed, 26 Mar 2014) | 7 lines
  
  iscsi-scst: Introduce ARRAY_SIZE()
  
  This patch does not change any functionality.
  
  Signed-off-by: Bart Van Assche <bvanassche@acm.org>
........
  r5387 | vlnb | 2014-03-26 05:22:16 +0200 (Wed, 26 Mar 2014) | 8 lines
  
  scst: Clarify a comment
  
  The comment above scst_nexus_loss() is somewhat confusing so change
  it into something that is more clear.
  
  Signed-off-by: Bart Van Assche <bvanassche@acm.org>
........
  r5388 | vlnb | 2014-03-26 05:23:57 +0200 (Wed, 26 Mar 2014) | 9 lines
  
  scst_vdisk: Fix READ CAPACITY(10)
  
  SBC-2 defines the LBA as a 32-bit field that starts at offset 2 and
  not as a 64-bit field.
  
  Reported-by: Mike Christie <michaelc@cs.wisc.edu>
  Signed-off-by: Bart Van Assche <bvanassche@acm.org>
........
  r5389 | bvassche | 2014-03-26 13:56:13 +0200 (Wed, 26 Mar 2014) | 4 lines
  
  ib_srpt: Clean up srpt_handle_rdma_comp()
  
  This patch does not change any functionality.
........
  r5390 | bvassche | 2014-03-26 13:56:59 +0200 (Wed, 26 Mar 2014) | 4 lines
  
  ib_srpt: Clean up srpt_handle_send_err_comp()
  
  This patch does not change any functionality.
........
  r5391 | bvassche | 2014-03-26 13:58:25 +0200 (Wed, 26 Mar 2014) | 4 lines
  
  ib_srpt: Clean up srpt_handle_rdma_err_comp()
  
  This patch does not change any functionality.
........
  r5392 | bvassche | 2014-03-26 13:59:37 +0200 (Wed, 26 Mar 2014) | 5 lines
  
  ib_srpt: Suppress superfluous error messages
  
  Only complain about a missing completion for I/O contexts that are
  in a state where the ib_srpt driver is waiting for the HCA.
........
  r5393 | bvassche | 2014-03-26 14:00:43 +0200 (Wed, 26 Mar 2014) | 5 lines
  
  ib_srpt: Make srpt_abort_cmd() state checks more strict
  
  Complain if srpt_abort_cmd() is called for an I/O context that is
  being processed by SCST and not by the HCA.
........
  r5394 | vlnb | 2014-03-27 00:16:16 +0200 (Thu, 27 Mar 2014) | 3 lines
  
  Cosmetics
........
  r5395 | vlnb | 2014-03-27 01:51:36 +0200 (Thu, 27 Mar 2014) | 3 lines
  
  Reimplement dropping of TM requests in a more reliable manner
........
  r5396 | vlnb | 2014-03-27 03:57:08 +0200 (Thu, 27 Mar 2014) | 3 lines
  
  Possibility to specify SCSI target device name added
........
  r5397 | bvassche | 2014-03-27 10:27:45 +0200 (Thu, 27 Mar 2014) | 6 lines
  
  Fix two checkpatch complaints about whitespace
  
  Avoid that checkpatch reports the following error message:
  
  ERROR: "(foo*)" should be "(foo *)"
........
  r5398 | bvassche | 2014-03-27 10:34:27 +0200 (Thu, 27 Mar 2014) | 6 lines
  
  Avoid that checkpatch complains that return is not a function
  
  Avoid that checkpatch reports the following error message:
  
  ERROR: return is not a function, parentheses are not required
........
  r5399 | bvassche | 2014-03-27 10:39:53 +0200 (Thu, 27 Mar 2014) | 1 line
  
  scripts/generate-kernel-patch: Fix for kernel versions 3.7, 3.10, 3.12 and 3.13
........
  r5400 | vlnb | 2014-03-29 04:07:22 +0300 (Sat, 29 Mar 2014) | 3 lines
  
  Cleanup
........
  r5401 | bvassche | 2014-04-01 20:46:36 +0300 (Tue, 01 Apr 2014) | 1 line
  
  vdisk_blockio: Temporarily disable COMPARE AND WRITE support
........
  r5402 | bvassche | 2014-04-02 00:05:31 +0300 (Wed, 02 Apr 2014) | 1 line
  
  vdisk_blockio: Fix the (recently enabled) VERIFY command
........
  r5403 | bvassche | 2014-04-03 18:58:16 +0300 (Thu, 03 Apr 2014) | 1 line
  
  ib_srpt: RHEL 6.5 build fix
........
  r5404 | vlnb | 2014-04-04 03:57:30 +0300 (Fri, 04 Apr 2014) | 3 lines
  
  Fix typo in scst_report_supported_tm_fns() reported by Steve Magnani <steve.magnani@digidescorp.com>
........
  r5405 | bvassche | 2014-04-04 07:38:33 +0300 (Fri, 04 Apr 2014) | 1 line
  
  scripts/specialize-patch: Handle numbers surrounded by parentheses properly
........
  r5406 | bvassche | 2014-04-04 08:50:52 +0300 (Fri, 04 Apr 2014) | 1 line
  
  scripts/specialize-patch: Rework r5405
........
  r5407 | bvassche | 2014-04-04 08:56:25 +0300 (Fri, 04 Apr 2014) | 1 line
  
  nightly build: Update kernel versions
........


git-svn-id: http://svn.code.sf.net/p/scst/svn/branches/iser@5408 d57e44dd-8a1f-0410-8b47-8ef2f437770f
2014-04-06 08:13:25 +00:00

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<h1>Generic SCSI Target Subsystem for Linux</h1>
<p>The generic SCSI target subsystem for Linux (SCST) allows creation of sophisticated storage devices
from any Linux box. Those
devices can provide advanced
functionality, like replication, thin provisioning,
deduplication, high availability,
automatic backup, etc. Another class of such devices
are Virtual Tape Libraries (VTL)
as well as other disk-based backup solutions.</p>
<p>SCST devices can use any link which supports
SCSI-style data exchange: <strong>iSCSI</strong>, <strong>Fibre Channel</strong>, <strong>FCoE</strong>,
<strong>SAS</strong>,
<strong>InfiniBand (SRP)</strong>, <strong>Wide (parallel) SCSI</strong>, etc.</p>
<p>It might
well be that your favorite storage appliance is running SCST in the firmware.</p>
<p>SCST project consists from a set of subprojects: generic SCSI target mid-layer itself (SCST core)
with a set of device handlers as well as target drivers
and user space utilities.
<h1>Features of SCST Core</h1>
<ul>
<li><span>SCST core provides unified,
consistent interface between SCSI target drivers and
Linux kernel as well as between Linux kernel and storage backend
handlers, connecting target drivers with real or emulated storage backend.</span></li>
<li><span>SCST core performs all required pre- and post- processing of incoming requests as well as
necessary error recovery.</span></li>
<li><span>SCST core undertakes most problems, related to execution contexts, thus practically eliminating one of the most
complicated problem in the kernel drivers development. For example, target drivers for Marvell
SAS adapters or for InfiniBand SRP are less 3000 lines of code long.</span></li>
<li><span>Very low overhead and fine-grained locks allow to reach the
maximum performance and scalability. Particularly, incoming requests can be processed in
the caller's context or in one of the internal SCST core's tasklets without any
extra context switches.</span></li>
<li><span>Device handlers architecture allows various I/O
modes in backstorage handling. For example, pass-through device handlers allow to export real
SCSI hardware and vdisk device handler allows to export files as virtual disks.</span></li>
<li><span>Advanced per-initiator devices visibility management (LUN masking) allows different
initiators to see different set of devices with different access permissions. For instance,
initiator A could see exported from target T devices X and Y read-writable, and initiator B from
the same target T could see devices Y read-only and Z read-writable.
This feature is required for hardware targets, which don't have ability to create
virtual targets (SAS adapters, for instance).</span></li>
<li><span>SCST core emulates necessary functionality of SCSI host adapter, because from remote initiators' point of view
a SCSI target acts as a SCSI host with its own devices. This is especially important in pass-through mode with
one to many relationship, i.e. when multiple initiators can connect to the exported pass-through
devices. You can find more deep elaboration why it is needed in <a href="http://www.mail-archive.com/linux-scsi@vger.kernel.org/msg06911.html">this</a>
message in thread "Question for pass-through target design" in linux-scsi mailing list. Some of the emulated functions are the following:</span>
<ul>
<li><span>Generation of necessary UNIT ATTENTIONs, their storage and delivery to all connected
remote initiators.</span></li>
<li><span>RESERVE/RELEASE functionality.</span></li>
<li><span>All types of RESETs and other task management functions.</span></li>
<li><span>REPORT LUNS command as well as SCSI address space management in order to have consistent
address space on all remote initiators, since local SCSI devices could not know about each
other to report via REPORT LUNS command. Additionally, SCST core responds with error on all
commands to non-existing devices and provides access control, so different remote
initiators could see different set of devices.</span></li>
<li><span>Other necessary functionality (task attributes, etc.) as specified in SCSI standards.</span></li>
</ul>
</li>
<li><span>SCST core has multithreaded design and complete SMP support, so, if necessary, all your CPU cores will participate in the commands
processing.</span></li>
<li><span>Well documented.</span></li>
</ul>
<p>Interoperability between remote and local SCSI initiators (i.e. sd, st, etc.) is the additional issue that SCST is going to
address (it is not implemented yet). It is necessary, because local SCSI initiators can change the state of the
device, for example RESERVE the device, or some of its parameters and that could be done behind SCST, i.e. remote initiators
will not know about it, which could
lead to various problems, including data corruption. Thus, RESERVE/RELEASE commands, locally generated
UNIT ATTENTIONs, etc. should be intercepted and passed through SCST core.</p>
<p>You can find comparison of SCST with other SCSI targets on the <a href="comparison.html">Comparison</a> page.
Some highlights what it can mean for end users you can find on the <a href="target_iscsi.html">iSCSI-SCST</a> page.
<h1>SCST core supports the following I/O modes</h1>
<ul>
<li><span>Pass-through mode with one to many relationship, i.e. when multiple initiators can
connect to the exported pass-through devices, for virtually all SCSI devices types: disks (type 0),
tapes (type 1), processors (type 3), CDROMs (type 5), MO disks (type 7), medium changers (type 8) and RAID
controllers (type 0xC). In this mode you can, for instance, share your parallel SCSI tape or SATA
DVD-RW device to your iSCSI network.</span></li>
<li><span>FILEIO mode, which allows to use files on file systems or block devices as virtual
remotely available SCSI disks or CDROMs with benefits of the Linux cache.</span></li>
<li><span>BLOCKIO mode, which performs direct block IO with a block device, bypassing
page-cache for all operations. This mode works well with high-end storage HBAs and for applications that
either do not need caching between application and disk or need the large block throughput.</span></li>
<li><span>User space mode using scst_user device handler, which allows to implement in the
user space high performance virtual SCSI devices. Comparing with fully in-kernel dev handlers
this mode has very low overhead (few %%).</span></li>
<li><span>Performance testing device handlers as well as NULLIO mode to provide
a way for direct performance measurements without overhead of actual data
transfers from/to underlying SCSI devices.
</span></li>
</ul>
<h1>Certification</h1>
<p>SCST core engine has passed VMware certification as part of
<a href="http://scalecomputing.com/products">Scale&rsquo;s Intelligent Clustered Storage</a> technology developed by
<a href="http://scalecomputing.com">Scale Computing</a> as well as VMware and Microsoft certification as part of
storage arrays developed by <a href="http://www.open-e.com/">Open-E, Inc</a> and
<a href="http://www.starboardstorage.com">Starboard Storage</a>.</p>
<p>As of October 2012 SCST-based Hewlett-Packard ProLiant BL465c Gen8 earned the maximum
score 59.99@62 tiles in <a href="http://www.vmware.com/a/vmmark">VMmark Version 2.1.1</a>.</p>
</div>
<div id="rightbar">
<h1>Documentation</h1>
<p><a href="scst_pg.html">HTML</a></p>
<p><a href="scst_pg.pdf">PDF</a></p>
<p><a href="http://monklinux.blogspot.com/2012/02/scst-configuration-how-to-using-gentoo.html">Gentoo HOWTO</a></p>
<p><a href="iscsi-scst-howto.txt">HOWTO For iSCSI-SCST</a></p>
<p><a href="SCST_Gentoo_HOWTO.txt">Gentoo HOWTO For iSCSI-SCST</a></p>
<p><a href="http://alpinelinux.org/wiki/High_performance_SCST_iSCSI_Target_on_Linux_software_Raid" class="readmore">Alpine Linux HOWTO</a></p>
<p><a href="qla2x00t-howto.html">HOWTO For QLogic Target Driver</a></p>
<p><a href="sgv_cache.html">SCST SGV Cache Description</a></p>
<h1>Articles</h1>
<p><a href="http://marcitland.blogspot.com/2011/03/accelerating-vdi-using-scst-and-ssds.html">Accelerating VDI Using SCST and SSDs</a>
by Marc Smith</p>
<h1>SCST 0.9.6 graphs</h1>
<p><a href="images/init_scst.png">init_scst</a></p>
<p><a href="images/scst_cmd_thread.png">scst_cmd_thread</a></p>
<p><a href="images/scst_mgmt_cmd_thread.png">scst_mgmt_cmd_thread</a></p>
<p><a href="images/scst_mgmt_thread.png">scst_mgmt_thread</a></p>
<p>all by Ming Zhang</p>
<h1>QUESTIONS</h1>
<p>If you have any questions you can ask them via<br><a href="http://lists.sourceforge.net/lists/listinfo/scst-devel">
scst-devel mailing list</a><br><br>
See <a href="http://sourceforge.net/mail/?group_id=110471">mailing lists page</a> for more info about SCST mailing
lists.</p>
<h1></h1>
<p><a href="http://sourceforge.net/donate/index.php?group_id=110471">
<img src="http://images.sourceforge.net/images/project-support.jpg" width="88" height="32" border="0" alt="Support This Project"> </a></p>
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