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iscsi-scst.md

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Configuration

Following this article, you basically:

  1. Make sure for i in scst{,_vdisk,_disk,_user} qla2xxx_scst qla2x00tgt; do modprobe $i; done won't give any errors (whether in terminal or in dmesg). For good measure, replace modprobe with echo, and then copy the output into /etc/modules, so it would be loaded on boot.
  2. Use scstadmin -list_target, scstadmin -list_handler, scstadmin -list_target to see what you've got. None of these lists should be empty.
  3. Create a /etc/scst.conf file, where you set options for HANDLER and TARGET_DRIVER. An example can be seen in man scst.conf. Note: if you configure TARGET_DRIVER qla2x00t, then inside it, in sub-paragraph TARGET 00:11:…, where the 00:11:… is a WWN of FC ports, which can be looked up at /sys/class/fc_host/host*/port_name. These params can also be seen at systool -c fc_host -v of sysfsutils package.
  4. Execute scstadmin -conf /etc/scst.conf

On errors in dmesg, whenever you see stuff like sqatgt: Missing parameter foo, the foo some_value has to be added in the scst.conf. scstadmin will write those into mgmt file, but you shouldn't do it manually, there's scstadmin for writing there with the right syntax.

Misc

  • LUN (Logical Unit Numbers): a device, which can be read/written from/to.
  • SCST handler is kinda like an SCST plugin to handle particular type of devices. E.g. to read from block device there's one plugin, from a file system another, and for cdrom there's yet another one. handlers are configured in scst.conf with a HANDLER section (see man scst.conf for example).
  • SCSI initiator: an endpoint (e.g. a computer) that initiates a session against the target
  • SCSI target: an endpoint that accepts a session from initiators, and provides them with LUNs.
  • configuring is done by writing a config file and executing scstadmin -config myconfig. Internally scstadmin configures by writing stuff into various files under /sys/kernel/scst_tgt. Stuff similar to the following: echo "add_target my_target" > /sys/kernel/scst_tgt/targets/iscsi/mgmt.
  • no initiator configuration is required. While setting up target, you also pass a WWN or IQN or whatever identifier of initiator, and then upon enabling target it will connect to initiator and you shall see a new block device in lsblk.
  • scst-created disks can be seen in lsscsi output

Typical problems

  • missing target files (ones with WWN) at /sys/kernel/scst_tgt/targets/qla2x00t/: check that /sys/module/qla2xxx_scst/parameters/qlini_mode is disabled. If isn't, add a line options qla2xxx_scst qlini_mode="disabled" under a /etc/modprobe.d dir and reload the qla2xxx_scst driver.

Debugging

Upon rebuilding you do rmmod iscsi_scst scst and then modprobe iscsi_scst.