/etc/target/saveconfig.json is the default location for storing the configuration of the Linux kernel target, also known as LIO. Since the target is in the kernel, tools like targetctl or targetcli must be used to save and restore the configuration across reboots.
Generating or modifying this file by hand, or with other tools, is also supported. This fills a gap for users whose needs are not met by the targetcli configuration shell, who cannot use the rtslib Python library, and yet also wish to avoid directly manipulating LIO's configfs interface.
The configuration file is in the "json" text format, which is both human- and machine-readable. Its format is very closely modeled on the layout and terminology that LIO uses. Attributes may be string, boolean, or numeric values. All sizes are expressed in bytes.
Top Level Summary
storage_objects describes mappings of resources on the local machine that can be used to emulate block devices.
fabric_modules describes settings for LIO fabrics -- the hardware or software protocols that transport SCSI commands -- such as iSCSI or Fibre Channel over Ethernet (FCoE).
targets describes the SCSI target endpoints that export storage objects over a fabric.
All storage objects must contain name and plugin values. Each name must be unique for all storage objects of its plugin type.
plugin must be one of: fileio, block, pscsi, or ramdisk.
Objects with plugin value of fileio must also contain dev, which is the full path to the file that is backing the storage object. Optional fileio attributes are wwn (string), write_back (boolean), and size (number). If the file given in dev does not exist, then size must be present, and a backing file of that size will be created.
Objects with plugin value of block must also contain dev, which is the full path to the block device that is backing the storage object. Optional block attributes are wwn (string), write_back (boolean), and readonly (boolean).
Objects with plugin value of pscsi must also contain dev, which is the full path to the SCSI device that is backing the storage object. There are no optional attributes.
Objects with plugin value of ramdisk must also contain size (number), which is the size in bytes of the ramdisk. Optional ramdisk attributes are wwn (string), and nullio (boolean).
All storage object definitions may also contain an attributes object. This contains LIO attribute values, all of which are also optional. Please see LIO documentation for more information on these.
This section is limited to setting discovery authentication settings for fabrics that support it (currently just iscsi). Objects here should contain name (e.g. "iscsi"), userid, password, mutual_userid, and mutual_password string values.
Target configuration is modeled on iSCSI, in which a named target can contain multiple sub-configurations called Target Port Groups (TPGs). LIO follows this model for describing configuration even for fabrics that do not support TPGs.
Objects in targets contain just three attributes: wwn is the world-wide name the target has been given. This may start with "iqn", or "naa", for example. fabric is the name of the fabric module this target is exported over. Allowed values for this depend on the system configuration, but examples include "iscsi", "loopback", and "tcm_fc". tpgs is a list of objects describing 1 or more TPGs, described below.
TPG object attributes are all optional. Values not supplied will be set to default values. tag (number) allows the tpg tag to be specified. enable (bool, default to true) allows the TPG to be disabled or enabled. luns, portals, and node_acls contain further lists of objects, descibed below. Finally, userid, password, mutual_userid, and mutual_password allow main-phase authentication values to be set for fabrics (like iSCSI) that support TPG-level authentication. (Please see targetcli(8) for details on TPG versus ACL-based authentication.) Finally, TPGs can also contain optional attributes and parameters lists, see LIO documentation for more information.
This list of objects maps storage objects to the TPG. index is a TPG-unique number for the assignment, which may be used as the LU number for fabrics that do not support ACL mappings. storage_object is a string linking back to a storage object, of the format "/backstores/<plugin>/<name>", where <plugin> and <name> correspond to a storage object defined under storage_objects.
Portals describe connection endpoints for iSCSI targets. Required values are ip_address (string) and port (number). iser (boolean) is an optional value to enable iSER. offload (boolean) is an optional value to enable hardware offload.
This contains information about explicit initiator LUN mappings. node_wwn (string) must be present. Authentication may also be set on a per-ACL basis with userid, password, mutual_userid, and mutual_password, similar to TPGs. mapped_luns is a list of mapped luns, described below. Finally, node_acls can contain an optional attributes list.
Objects in mapped_luns contain three required attributes. write_protect (boolean) sets the write-protect status of the mapped LUN. tpg_lun (number) corresponds to an existing entry in the TPG's luns list. index is the LU number that the mapped LUN will claim.
Since tools generate this file, one good way to understand its format is to use a tool like targetcli to configure a target, then run saveconfig, and view the resulting json file.
Man page written by Andy Grover <firstname.lastname@example.org>.
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