1 .\" Copyright (c) 2013 Edward Tomasz Napierala
2 .\" Copyright (c) 2015-2017 Alexander Motin <mav@FreeBSD.org>
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32 .Nd CAM Target Layer / iSCSI target subsystem
34 To compile this driver into the kernel,
35 place the following line in your
36 kernel configuration file:
37 .Bd -ragged -offset indent
42 Alternatively, to load the driver as a
43 module at boot time, place the following line in
45 .Bd -literal -offset indent
51 subsystem provides SCSI target devices emulation.
52 It supports features such as:
56 Disk, CD-ROM and processor device emulation
60 SCSI task attribute support (ordered, head of queue, simple tags)
62 SCSI implicit command ordering support
64 Full task management support (abort, query, reset, etc.)
66 Support for multiple ports, initiators, targets and backing stores
68 Support for VMWare VAAI and Microsoft ODX offload (COMPARE AND WRITE,
69 XCOPY, POPULATE TOKEN/WRITE USING TOKEN, WRITE SAME and UNMAP)
71 Persistent reservation support
73 Extensive VPD/mode/log pages support
75 Featured error reporting, error injection and basic SMART support
77 High Availability clustering support with ALUA
79 All I/O handled in-kernel, no userland context switch overhead
84 subsystem includes multiple frontends to provide access using different
85 transport protocols and implementations:
86 .Bl -tag -width cfumass
88 Provides access for local system via virtual initiator mode
92 Provides access for remote systems via target mode
94 SIMs, such as Fibre Channel
99 Provides access for remote systems via USB Mass Storage Class
100 Bulk Only (BBB) Transport.
102 Internal frontend used to receive requests from other node ports in
103 High Availability cluster.
105 Provides access for local user-level applications via
113 provides access for remote systems via iSCSI protocol.
115 Internal frontend used to receive requests from Third Party Copy engine,
116 implementing copy offload operations.
121 subsystem includes two backends to create logical units using different
122 kinds of backing stores:
123 .Bl -tag -width ramdisk
125 Stores data in ZFS ZVOLs, files or raw block devices.
127 Stores data in RAM, that makes it mostly useful for performance testing.
128 Depending on configured capacity can work as black hole, thin or thick
132 The following variables are available as both
137 .Bl -tag -width indent
138 .It Va kern.cam.ctl.debug
139 Bit mask of enabled CTL log levels:
140 .Bl -tag -offset indent -compact
142 log commands with errors;
146 log data for commands other then READ/WRITE.
149 .It Va kern.cam.ctl.ha_id
150 Specifies unique position of this node within High Availability cluster.
151 Default is 0 -- no HA, 1 and 2 -- HA enabled at specified position.
152 .It Va kern.cam.ctl.ha_mode
153 Specifies High Availability cluster operation mode:
154 .Bl -tag -offset indent -compact
156 Active/Standby -- primary node has backend access and processes requests,
157 while secondary can only do basic LUN discovery and reservation;
159 Active/Active -- both nodes have backend access and process requests,
160 while secondary node synchronizes processing with primary one;
162 Active/Active -- primary node has backend access and processes requests,
163 while secondary node forwards all requests and data to primary one;
165 All above modes require established connection between HA cluster nodes.
166 If connection is not configured, secondary node will report Unavailable
167 state; if configured but not established -- Transitioning state.
169 .It Va kern.cam.ctl.ha_peer
170 String value, specifying method to establish connection to peer HA node.
171 Can be "listen IP:port", "connect IP:port" or empty.
172 .It Va kern.cam.ctl.ha_link
173 Reports present state of connection between HA cluster nodes:
174 .Bl -tag -offset indent -compact
178 configured but not established;
182 .It Va kern.cam.ctl.ha_role
183 Specifies default role of this node:
184 .Bl -tag -offset indent -compact
190 This role can be overridden on per-LUN basis using "ha_role" LUN option,
191 so that for one LUN one node is primary, while for another -- another.
192 Role change from primary to secondary for HA modes 0 and 2 closes backends,
193 the opposite change -- opens.
194 If there is no primary node (both nodes are secondary, or secondary node has
195 no connection to primary one), secondary node(s) report Transitioning state.
196 State with two primary nodes is illegal (split brain condition).
197 .It Va kern.cam.ctl.iscsi.debug
198 Verbosity level for log messages from the kernel part of iSCSI target.
199 Set to 0 to disable logging or 1 to warn about potential problems.
200 Larger values enable debugging output.
202 .It Va kern.cam.ctl.iscsi.maxtags
203 The number of outstanding commands to advertise to each iSCSI initiator.
204 Current implementation is not very accurate, so do not set this below 2.
206 .It Va kern.cam.ctl.iscsi.ping_timeout
207 The number of seconds to wait for the iSCSI initiator to respond to a NOP-In
209 In the event that there is no response within that time the session gets
211 Set to 0 to disable sending NOP-In PDUs.
222 subsystem first appeared in
227 subsystem was originally written by
228 .An Kenneth Merry Aq Mt ken@FreeBSD.org .
229 Later work was done by
230 .An Alexander Motin Aq Mt mav@FreeBSD.org .