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Message-ID: <4BC46D5A.9030003@vlnb.net>
Date: Tue, 13 Apr 2010 17:10:50 +0400
From: Vladislav Bolkhovitin <vst@...b.net>
To: linux-scsi@...r.kernel.org
CC: linux-kernel@...r.kernel.org,
scst-devel <scst-devel@...ts.sourceforge.net>,
James Bottomley <James.Bottomley@...senPartnership.com>,
Andrew Morton <akpm@...ux-foundation.org>,
FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
Mike Christie <michaelc@...wisc.edu>,
Jeff Garzik <jeff@...zik.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Bart Van Assche <bart.vanassche@...il.com>
Subject: Re: [PATCH][RFC 4/4/4/5] iSCSI-SCST's README file
This patch contains iSCSI-SCST's README file.
Signed-off-by: Vladislav Bolkhovitin <vst@...b.net>
---
README.iscsi | 585 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 585 insertions(+)
diff -uprN orig/linux-2.6.33/Documentation/scst/README.iscsi linux-2.6.33/Documentation/scst/README.iscsi
--- orig/linux-2.6.33/Documentation/scst/README.iscsi
+++ linux-2.6.33/Documentation/scst/README.iscsi
@@ -0,0 +1,585 @@
+iSCSI SCST target driver
+========================
+
+ISCSI-SCST is a deeply reworked fork of iSCSI Enterprise Target (IET)
+(http://iscsitarget.sourceforge.net). Reasons of the fork were:
+
+ - To be able to use full power of SCST core.
+
+ - To fix all the problems, corner cases issues and iSCSI standard
+ violations which IET has.
+
+See more info at http://iscsi-scst.sourceforge.net.
+
+Usage
+-----
+
+See in http://iscsi-scst.sourceforge.net/iscsi-scst-howto.txt how to
+configure iSCSI-SCST.
+
+In 2.0.0 usage of iscsi-scstd.conf as well as iscsi-scst-adm utility is
+obsolete. Use the sysfs interface facilities instead.
+
+It is recommended to use TEST UNIT READY ("tur") command to check if
+iSCSI-SCST target is alive in MPIO configurations.
+
+Also see SCST README file how to tune for the best performance.
+
+CAUTION: Working of target and initiator on the same host isn't fully
+======= supported. See SCST README file for details.
+
+Sysfs interface
+---------------
+
+Root of SCST sysfs interface is /sys/kernel/scst_tgt. Root of iSCSI-SCST
+is /sys/kernel/scst_tgt/targets/iscsi. It has the following entries:
+
+ - None, one or more subdirectories for targets with name equal to names
+ of the corresponding targets.
+
+ - IncomingUser[num] - optional one or more attributes containing user
+ name and password for incoming discovery user name. Not exist by
+ default and can be added through "mgmt" entry, see below.
+
+ - OutgoingUser - optional attribute containing user name and password
+ for outgoing discovery user name. Not exist by default and can be
+ added through "mgmt" entry, see below.
+
+ - iSNSServer - contains name or IP address of iSNS server with optional
+ "AccessControl" attribute, which allows to enable iSNS access
+ control. Empty by default.
+
+ - enabled - using this attribute you can enable or disable iSCSI-SCST
+ accept new connections. It allows to finish configuring global
+ iSCSI-SCST attributes before it starts accepting new connections. 0
+ by default.
+
+ - open_state - read-only attribute, which allows to see if the user
+ space part of iSCSI-SCST connected to the kernel part.
+
+ - trace_level - allows to enable and disable various tracing
+ facilities. See content of this file for help how to use it.
+
+ - version - read-only attribute, which allows to see version of
+ iSCSI-SCST and enabled optional features.
+
+ - mgmt - main management entry, which allows to configure iSCSI-SCST.
+ Namely, add/delete targets as well as add/delete optional global and
+ per-target attributes. See content of this file for help how to use
+ it.
+
+Each iSCSI-SCST sysfs file (attribute) can contain in the last line mark
+"[key]". It is automatically added mark used to allow scstadmin to see
+which attributes it should save in the config file. You can ignore it.
+
+Each target subdirectory contains the following entries:
+
+ - ini_groups - subdirectory defining initiator groups for this target,
+ used to define per-initiator access control. See SCST core README for
+ more details.
+
+ - luns - subdirectory defining LUNs of this target. See SCST core
+ README for more details.
+
+ - sessions - subdirectory containing connected to this target sessions.
+
+ - IncomingUser[num] - optional one or more attributes containing user
+ name and password for incoming user name. Not exist by default and can
+ be added through the "mgmt" entry, see above.
+
+ - OutgoingUser - optional attribute containing user name and password
+ for outgoing user name. Not exist by default and can be added through
+ the "mgmt" entry, see above.
+
+ - Entries defining default iSCSI parameters values used during iSCSI
+ parameters negotiation. Only entries which can be changed or make
+ sense are listed there.
+
+ - QueuedCommands - defines maximum number of commands queued to any
+ session of this target. Default is 32 commands.
+
+ - RspTimeout - defines the maximum time in seconds a command can wait for
+ response from initiator, otherwise the corresponding connection will
+ be closed. For performance reasons it is implemented as a timer,
+ which once in RspTimeout time checks the oldest command waiting for
+ response and, if it's older than RspTimeout, then it closes the
+ connection. Hence, a stalled connection will be closed in time
+ between RspTimeout and 2*RspTimeout. Default is 30 seconds.
+
+ - NopInInterval - defines interval between NOP-In requests, which the
+ target will send on idle connections to check if the initiator is
+ still alive. If there is no NOP-Out reply from the initiator in
+ RspTimeout time, the corresponding connection will be closed. Default
+ is 30 seconds. If it's set to 0, then NOP-In requests are disabled.
+
+ - enabled - using this attribute you can enable or disable iSCSI-SCST
+ accept new connections to this target. It allows to finish
+ configuring it before it starts accepting new connections. 0 by
+ default.
+
+ - rel_tgt_id - allows to read or write SCSI Relative Target Port
+ Identifier attribute. This identifier is used to identify SCSI Target
+ Ports by some SCSI commands, mainly by Persistent Reservations
+ commands. This identifier must be unique among all SCST targets, but
+ for convenience SCST allows disabled targets to have not unique
+ rel_tgt_id. In this case SCST will not allow to enable this target
+ until rel_tgt_id becomes unique. This attribute initialized unique by
+ SCST by default.
+
+ - tid - TID of this target.
+
+Subdirectory "sessions" contains one subdirectory for each connected
+session with name equal to name of the connected initiator.
+
+Each session subdirectory contains the following entries:
+
+ - One subdirectory for each TCP connection in this session. ISCSI-SCST
+ supports 1 connection per session, but the session subdirectory can
+ contain several connections: one active and other being closed.
+
+ - Entries defining negotiated iSCSI parameters. Only parameters which
+ can be changed or make sense are listed there.
+
+ - initiator_name - contains initiator name
+
+ - sid - contains SID of this session
+
+ - reinstating - contains reinstatement state of this session
+
+ - force_close - write-only attribute, which allows to force close this
+ session. This is the only writable session attribute.
+
+ - active_commands - contains number of active, i.e. not yet or being
+ executed, SCSI commands in this session.
+
+ - commands - contains overall number of SCSI commands in this session.
+
+Each connection subdirectory contains the following entries:
+
+ - cid - contains CID of this connection.
+
+ - ip - contains IP address of the connected initiator.
+
+ - state - contains processing state of this connection.
+
+Below is a sample script, which configures 1 virtual disk "disk1" using
+/disk1 image and one target iqn.2006-10.net.vlnb:tgt with all default
+parameters:
+
+#!/bin/bash
+
+modprobe scst
+modprobe scst_vdisk
+
+echo "add_device disk1 filename=/disk1; nv_cache=1" >/sys/kernel/scst_tgt/handlers/vdisk_fileio/mgmt
+
+service iscsi-scst start
+
+echo "add_target iqn.2006-10.net.vlnb:tgt" >/sys/kernel/scst_tgt/targets/iscsi/mgmt
+echo "add disk1 0" >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt/luns/mgmt
+
+echo 1 >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt/enabled
+echo 1 >/sys/kernel/scst_tgt/targets/iscsi/enabled
+
+Below is more advanced sample script, which configures more virtual
+devices of various types, including virtual CDROM and 2 targets, one
+with all default parameters, another one with some not default
+parameters, incoming and outgoing user names for CHAP authentification,
+and special permissions for initiator iqn.2005-03.org.open-iscsi:cacdcd2520,
+which will see another set of devices. Also this sample configures CHAP
+authentication for discovery sessions and iSNS server with access control.
+
+#!/bin/bash
+
+modprobe scst
+modprobe scst_vdisk
+
+echo "add_device disk1 filename=/disk1; nv_cache=1" >/sys/kernel/scst_tgt/handlers/vdisk_fileio/mgmt
+echo "add_device disk2 filename=/disk2; blocksize=4096; nv_cache=1" >/sys/kernel/scst_tgt/handlers/vdisk_fileio/mgmt
+echo "add_device blockio filename=/dev/sda5" >/sys/kernel/scst_tgt/handlers/vdisk_blockio/mgmt
+echo "add_device nullio" >/sys/kernel/scst_tgt/handlers/vdisk_nullio/mgmt
+echo "add_device cdrom" >/sys/kernel/scst_tgt/handlers/vcdrom/mgmt
+
+service iscsi-scst start
+
+echo "192.168.1.16 AccessControl" >/sys/kernel/scst_tgt/targets/iscsi/iSNSServer
+echo "add_attribute IncomingUser joeD 12charsecret" >/sys/kernel/scst_tgt/targets/iscsi/mgmt
+echo "add_attribute OutgoingUser jackD 12charsecret1" >/sys/kernel/scst_tgt/targets/iscsi/mgmt
+
+echo "add_target iqn.2006-10.net.vlnb:tgt" >/sys/kernel/scst_tgt/targets/iscsi/mgmt
+
+echo "add disk1 0" >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt/luns/mgmt
+echo "add cdrom 1" >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt/luns/mgmt
+
+echo "add_target iqn.2006-10.net.vlnb:tgt1" >/sys/kernel/scst_tgt/targets/iscsi/mgmt
+echo "add_target_attribute iqn.2006-10.net.vlnb:tgt1 IncomingUser1 joe2 12charsecret2" >/sys/kernel/scst_tgt/targets/iscsi/mgmt
+echo "add_target_attribute iqn.2006-10.net.vlnb:tgt1 IncomingUser joe 12charsecret" >/sys/kernel/scst_tgt/targets/iscsi/mgmt
+echo "add_target_attribute iqn.2006-10.net.vlnb:tgt1 OutgoingUser jim1 12charpasswd" >/sys/kernel/scst_tgt/targets/iscsi/mgmt
+echo "No" >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt1/InitialR2T
+echo "Yes" >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt1/ImmediateData
+echo "8192" >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt1/MaxRecvDataSegmentLength
+echo "8192" >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt1/MaxXmitDataSegmentLength
+echo "131072" >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt1/MaxBurstLength
+echo "32768" >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt1/FirstBurstLength
+echo "1" >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt1/MaxOutstandingR2T
+echo "CRC32C,None" >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt1/HeaderDigest
+echo "CRC32C,None" >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt1/DataDigest
+echo "32" >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt1/QueuedCommands
+
+echo "add disk2 0" >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt1/luns/mgmt
+echo "add nullio 26" >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt1/luns/mgmt
+
+echo "create special_ini" >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt1/ini_groups/mgmt
+echo "add blockio 0 read_only=1" >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt1/ini_groups/special_ini/luns/mgmt
+echo "add iqn.2005-03.org.open-iscsi:cacdcd2520" >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt1/ini_groups/special_ini/initiators/mgmt
+
+echo 1 >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt/enabled
+echo 1 >/sys/kernel/scst_tgt/targets/iscsi/iqn.2006-10.net.vlnb:tgt1/enabled
+
+echo 1 >/sys/kernel/scst_tgt/targets/iscsi/enabled
+
+The resulting overall SCST sysfs hierarchy with an initiator connected to
+both iSCSI-SCST targets will look like:
+
+/sys/kernel/scst_tgt
+|-- devices
+| |-- blockio
+| | |-- blocksize
+| | |-- exported
+| | | `-- export0 -> ../../../targets/iscsi/iqn.2006-10.net.vlnb:tgt1/ini_groups/special_ini/luns/0
+| | |-- filename
+| | |-- handler -> ../../handlers/vdisk_blockio
+| | |-- read_only
+| | |-- removable
+| | |-- resync_size
+| | |-- size_mb
+| | |-- t10_dev_id
+| | |-- threads_num
+| | |-- threads_pool_type
+| | |-- type
+| | `-- usn
+| |-- cdrom
+| | |-- exported
+| | | `-- export0 -> ../../../targets/iscsi/iqn.2006-10.net.vlnb:tgt/luns/1
+| | |-- filename
+| | |-- handler -> ../../handlers/vcdrom
+| | |-- size_mb
+| | |-- t10_dev_id
+| | |-- threads_num
+| | |-- threads_pool_type
+| | |-- type
+| | `-- usn
+| |-- disk1
+| | |-- blocksize
+| | |-- exported
+| | | `-- export0 -> ../../../targets/iscsi/iqn.2006-10.net.vlnb:tgt/luns/0
+| | |-- filename
+| | |-- handler -> ../../handlers/vdisk_fileio
+| | |-- nv_cache
+| | |-- o_direct
+| | |-- read_only
+| | |-- removable
+| | |-- resync_size
+| | |-- size_mb
+| | |-- t10_dev_id
+| | |-- type
+| | |-- usn
+| | `-- write_through
+| |-- disk2
+| | |-- blocksize
+| | |-- exported
+| | | `-- export0 -> ../../../targets/iscsi/iqn.2006-10.net.vlnb:tgt1/luns/0
+| | |-- filename
+| | |-- handler -> ../../handlers/vdisk_fileio
+| | |-- nv_cache
+| | |-- o_direct
+| | |-- read_only
+| | |-- removable
+| | |-- resync_size
+| | |-- size_mb
+| | |-- t10_dev_id
+| | |-- threads_num
+| | |-- threads_pool_type
+| | |-- threads_num
+| | |-- threads_pool_type
+| | |-- type
+| | |-- usn
+| | `-- write_through
+| `-- nullio
+| |-- blocksize
+| |-- exported
+| | `-- export0 -> ../../../targets/iscsi/iqn.2006-10.net.vlnb:tgt1/luns/26
+| |-- handler -> ../../handlers/vdisk_nullio
+| |-- read_only
+| |-- removable
+| |-- size_mb
+| |-- t10_dev_id
+| |-- threads_num
+| |-- threads_pool_type
+| |-- type
+| `-- usn
+|-- handlers
+| |-- vcdrom
+| | |-- cdrom -> ../../devices/cdrom
+| | |-- mgmt
+| | |-- trace_level
+| | `-- type
+| |-- vdisk_blockio
+| | |-- blockio -> ../../devices/blockio
+| | |-- mgmt
+| | |-- trace_level
+| | `-- type
+| |-- vdisk_fileio
+| | |-- disk1 -> ../../devices/disk1
+| | |-- disk2 -> ../../devices/disk2
+| | |-- mgmt
+| | |-- trace_level
+| | `-- type
+| `-- vdisk_nullio
+| |-- mgmt
+| |-- nullio -> ../../devices/nullio
+| |-- trace_level
+| `-- type
+|-- sgv
+| |-- global_stats
+| |-- sgv
+| | `-- stats
+| |-- sgv-clust
+| | `-- stats
+| `-- sgv-dma
+| `-- stats
+|-- targets
+| `-- iscsi
+| |-- IncomingUser
+| |-- OutgoingUser
+| |-- enabled
+| |-- iSNSServer
+| |-- iqn.2006-10.net.vlnb:tgt
+| | |-- DataDigest
+| | |-- FirstBurstLength
+| | |-- HeaderDigest
+| | |-- ImmediateData
+| | |-- InitialR2T
+| | |-- MaxBurstLength
+| | |-- MaxOutstandingR2T
+| | |-- MaxRecvDataSegmentLength
+| | |-- MaxXmitDataSegmentLength
+| | |-- NopInInterval
+| | |-- QueuedCommands
+| | |-- RspTimeout
+| | |-- enabled
+| | |-- ini_groups
+| | | `-- mgmt
+| | |-- luns
+| | | |-- 0
+| | | | |-- device -> ../../../../../devices/disk1
+| | | | `-- read_only
+| | | |-- 1
+| | | | |-- device -> ../../../../../devices/cdrom
+| | | | `-- read_only
+| | | `-- mgmt
+| | |-- rel_tgt_id
+| | |-- sessions
+| | | `-- iqn.2005-03.org.open-iscsi:cacdcd2520
+| | | |-- 10.170.75.2
+| | | | |-- cid
+| | | | |-- ip
+| | | | `-- state
+| | | |-- DataDigest
+| | | |-- FirstBurstLength
+| | | |-- HeaderDigest
+| | | |-- ImmediateData
+| | | |-- InitialR2T
+| | | |-- MaxBurstLength
+| | | |-- MaxOutstandingR2T
+| | | |-- MaxRecvDataSegmentLength
+| | | |-- MaxXmitDataSegmentLength
+| | | |-- active_commands
+| | | |-- commands
+| | | |-- force_close
+| | | |-- initiator_name
+| | | |-- luns -> ../../luns
+| | | |-- reinstating
+| | | `-- sid
+| | `-- tid
+| |-- iqn.2006-10.net.vlnb:tgt1
+| | |-- DataDigest
+| | |-- FirstBurstLength
+| | |-- HeaderDigest
+| | |-- ImmediateData
+| | |-- IncomingUser
+| | |-- IncomingUser1
+| | |-- InitialR2T
+| | |-- MaxBurstLength
+| | |-- MaxOutstandingR2T
+| | |-- MaxRecvDataSegmentLength
+| | |-- MaxXmitDataSegmentLength
+| | |-- OutgoingUser
+| | |-- NopInInterval
+| | |-- QueuedCommands
+| | |-- RspTimeout
+| | |-- enabled
+| | |-- ini_groups
+| | | |-- mgmt
+| | | `-- special_ini
+| | | |-- initiators
+| | | | |-- iqn.2005-03.org.open-iscsi:cacdcd2520
+| | | | `-- mgmt
+| | | `-- luns
+| | | |-- 0
+| | | | |-- device -> ../../../../../../../devices/blockio
+| | | | `-- read_only
+| | | `-- mgmt
+| | |-- luns
+| | | |-- 0
+| | | | |-- device -> ../../../../../devices/disk2
+| | | | `-- read_only
+| | | |-- 26
+| | | | |-- device -> ../../../../../devices/nullio
+| | | | `-- read_only
+| | | `-- mgmt
+| | |-- rel_tgt_id
+| | |-- sessions
+| | | `-- iqn.2005-03.org.open-iscsi:cacdcd2520
+| | | |-- 10.170.75.2
+| | | | |-- cid
+| | | | |-- ip
+| | | | `-- state
+| | | |-- DataDigest
+| | | |-- FirstBurstLength
+| | | |-- HeaderDigest
+| | | |-- ImmediateData
+| | | |-- InitialR2T
+| | | |-- MaxBurstLength
+| | | |-- MaxOutstandingR2T
+| | | |-- MaxRecvDataSegmentLength
+| | | |-- MaxXmitDataSegmentLength
+| | | |-- active_commands
+| | | |-- commands
+| | | |-- force_close
+| | | |-- initiator_name
+| | | |-- luns -> ../../ini_groups/special_ini/luns
+| | | |-- reinstating
+| | | `-- sid
+| | `-- tid
+| |-- mgmt
+| |-- open_state
+| |-- trace_level
+| `-- version
+|-- threads
+|-- trace_level
+`-- version
+
+Troubleshooting
+---------------
+
+If you have any problems, start troubleshooting from looking at the
+kernel and system logs. In the kernel log iSCSI-SCST and SCST core send
+their messages, in the system log iscsi-scstd sends its messages. In
+most Linux distributions both those logs are put to /var/log/messages
+file.
+
+Then, it might be helpful to increase level of logging. For kernel
+modules you should make the debug build by enabling CONFIG_SCST_DEBUG.
+
+If after looking on the logs the reason of your problem is still unclear
+for you, report to SCST mailing list scst-devel@...ts.sourceforge.net.
+
+Work if target's backstorage or link is too slow
+------------------------------------------------
+
+In some cases you can experience I/O stalls or see in the kernel log
+abort or reset messages. It can happen under high I/O load, when your
+target's backstorage gets overloaded, or working over a slow link, when
+the link can't serve all the queued commands on time,
+
+To workaround it you can reduce QueuedCommands parameter for the
+corresponding target to some lower value, like 8 (default is 32).
+
+Also see SCST README file for more details about that issue and ways to
+prevent it.
+
+Performance advices
+-------------------
+
+1. If you use Windows XP or Windows 2003+ as initiators, you should
+consider to decrease TcpAckFrequency parameter to 1. See
+http://support.microsoft.com/kb/328890/ or google for "TcpAckFrequency"
+for more details.
+
+2. See how to get the maximum throughput from iSCSI, for instance, at
+http://virtualgeek.typepad.com/virtual_geek/2009/01/a-multivendor-post-to-help-our-mutual-iscsi-customers-using-vmware.html.
+It's about VMware, but its recommendations apply to other environments
+as well.
+
+3. ISCSI initiators built in pre-CentOS/RHEL 5 reported to have some
+performance problems. If you use it, it is strongly advised to upgrade.
+
+4. If you are going to use your target in an VM environment, for
+instance as a shared storage with VMware, make sure all your VMs
+connected to the target via *separate* sessions, i.e. each VM has own
+connection to the target, not all VMs connected using a single
+connection. You can check it using SCST sysfs interface. If you
+miss it, you can greatly loose performance of parallel access to your
+target from different VMs. This isn't related to the case if your VMs
+are using the same shared storage, like with VMFS, for instance. In this
+case all your VM hosts will be connected to the target via separate
+sessions, which is enough.
+
+5. Many dual port network adapters are not able to transfer data
+simultaneously on both ports, i.e. they transfer data via both ports on
+the same speed as via any single port. Thus, using such adapters in MPIO
+configuration can't improve performance. To allow MPIO to have double
+performance you should either use separate network adapters, or find a
+dual-port adapter capable to to transfer data simultaneously on both
+ports. You can check it by running 2 iperf's through both ports in
+parallel.
+
+6. Since network offload works much better in the write direction, than
+for reading (simplifying, in the read direction often there's additional
+data copy) in many cases with 10GbE in a single initiator-target pair
+the initiator's CPU is a bottleneck, so you can see the initiator can
+read data on much slower rate, than write. You can check it by watching
+*each particular* CPU load to find out if any of them is close to 100%
+load, including IRQ processing load. Note, many tools like vmstat give
+aggregate load on all CPUs, so with 4 cores 25% corresponds to 100% load
+of any single CPU.
+
+7. See SCST core's README for more advices. Especially pay attention to
+have io_grouping_type option set correctly.
+
+Compilation options
+-------------------
+
+There are the following compilation options, that could be commented
+in/out in the kernel's module Makefile:
+
+ - CONFIG_SCST_DEBUG - turns on some debugging code, including some logging.
+ Makes the driver considerably bigger and slower, producing large amount of
+ log data.
+
+ - CONFIG_SCST_TRACING - turns on ability to log events. Makes the driver
+ considerably bigger and leads to some performance loss.
+
+ - CONFIG_SCST_EXTRACHECKS - adds extra validity checks in the various places.
+
+ - CONFIG_SCST_ISCSI_DEBUG_DIGEST_FAILURES - simulates digest failures in
+ random places.
+
+Credits
+-------
+
+Thanks to:
+
+ * Ming Zhang <blackmagic02881@...il.com> for fixes
+
+ * Krzysztof Blaszkowski <kb@...mikro.com.pl> for many fixes
+
+ * Alexey Kuznetsov <kuznet@....inr.ac.ru> for comments and help in
+ debugging
+
+ * Tomasz Chmielewski <mangoo@...g.org> for testing and suggestions
+
+ * Bart Van Assche <bart.vanassche@...il.com> for a lot of help
+
+Vladislav Bolkhovitin <vst@...b.net>, http://scst.sourceforge.net
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