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CTL(4)                 FreeBSD Kernel Interfaces Manual                 CTL(4)

NAME
     ctl - CAM Target Layer

SYNOPSIS
     To compile this driver into the kernel, place the following line in your
     kernel configuration file:

           device ctl

     Alternatively, to load the driver as a module at boot time, place the
     following line in loader.conf(5):

           ctl_load="YES"

DESCRIPTION
     The ctl subsystem provides SCSI target devices emulation.  It supports
     features such as:

        Disk, CD-ROM and processor device emulation
        Tagged queueing
        SCSI task attribute support (ordered, head of queue, simple tags)
        SCSI implicit command ordering support
        Full task management support (abort, query, reset, etc.)
        Support for multiple ports, initiators, targets and backing stores
        Support for VMWare VAAI and Microsoft ODX offload (COMPARE AND WRITE,
         XCOPY, POPULATE TOKEN/WRITE USING TOKEN, WRITE SAME and UNMAP)
        Persistent reservation support
        Extensive VPD/mode/log pages support
        Featured error reporting, error injection and basic SMART support
        High Availability clustering support with ALUA
        All I/O handled in-kernel, no userland context switch overhead

     The ctl subsystem includes multiple frontends to provide access using
     different transport protocols and implementations:

     camsim   Provides access for local system via virtual initiator mode
              CAM(4) SIM.

     camtgt   Provides access for remote systems via target mode CAM(4) SIMs,
              such as Fibre Channel isp(4) and mpt(4).

     cfumass  Provides access for remote systems via USB Mass Storage Class
              Bulk Only (BBB) Transport.

     ha       Internal frontend used to receive requests from other node ports
              in High Availability cluster.

     ioctl    Provides access for local user-level applications via ioctl(2)
              based API.

     iscsi    Provides access for remote systems via the iSCSI protocol using
              cfiscsi(4).

     tpc      Internal frontend used to receive requests from Third Party Copy
              engine, implementing copy offload operations.

     The ctl subsystem includes two backends to create logical units using
     different kinds of backing stores:

     block    Stores data in ZFS ZVOLs, files or raw block devices.

     ramdisk  Stores data in RAM, that makes it mostly useful for performance
              testing.  Depending on configured capacity can work as black
              hole, thin or thick provisioned disk.

SYSCTL VARIABLES
     The following variables are available as both sysctl(8) variables and
     loader(8) tunables:

     kern.cam.ctl.debug
             Bit mask of enabled CTL log levels:
                   1       log commands with errors;
                   2       log all commands;
                   4       log data for commands other then READ/WRITE.
             Defaults to 0.

     kern.cam.ctl.ha_id
             Specifies unique position of this node within High Availability
             cluster.  Default is 0 -- no HA, 1 and 2 -- HA enabled at
             specified position.

     kern.cam.ctl.ha_mode
             Specifies High Availability cluster operation mode:
                   0       Active/Standby -- primary node has backend access
                           and processes requests, while secondary can only do
                           basic LUN discovery and reservation;
                   1       Active/Active -- both nodes have backend access and
                           process requests, while secondary node synchronizes
                           processing with primary one;
                   2       Active/Active -- primary node has backend access
                           and processes requests, while secondary node
                           forwards all requests and data to primary one;
             All above modes require established connection between HA cluster
             nodes.  If connection is not configured, secondary node will
             report Unavailable state; if configured but not established --
             Transitioning state.  Defaults to 0.

     kern.cam.ctl.ha_peer
             String value, specifying method to establish connection to peer
             HA node.  Can be "listen IP:port", "connect IP:port" or empty.

     kern.cam.ctl.ha_link
             Reports present state of connection between HA cluster nodes:
                   0       not configured;
                   1       configured but not established;
                   2       established.

     kern.cam.ctl.ha_role
             Specifies default role of this node:
                   0       primary;
                   1       secondary.
             This role can be overridden on per-LUN basis using "ha_role" LUN
             option, so that for one LUN one node is primary, while for
             another -- another.  Role change from primary to secondary for HA
             modes 0 and 2 closes backends, the opposite change -- opens.  If
             there is no primary node (both nodes are secondary, or secondary
             node has no connection to primary one), secondary node(s) report
             Transitioning state.  State with two primary nodes is illegal
             (split brain condition).

SEE ALSO
     cfiscsi(4), cfumass(4), ctladm(8), ctld(8), ctlstat(8)

HISTORY
     The ctl subsystem first appeared in FreeBSD 9.1.

AUTHORS
     The ctl subsystem was originally written by Kenneth Merry
     <[email protected]>.  Later work was done by
     Alexander Motin <[email protected]>.

FreeBSD 11.1-RELEASE-p4         March 29, 2017         FreeBSD 11.1-RELEASE-p4
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