iSCSI introduction and usage

Zhu Lingshan

lszhu@suse.com

What is SCSI

Small Computer System Interface(SCSI) is a set of standards for physically

connecting and transferring data between computers and peripheral devices. The

SCSI standards define commands, protocols, electrical and optical interfaces.

SCSI is most commonly used for hard disk drives and tape drives, but it can

connect a wide range of other devices, including scanners and CD drives,

although not all controllers can handle all devices. The SCSI standard defines

command sets for specific peripheral device types; the presence of "unknown" as

one of these types means that in theory it can be used as an interface to almost

any device, but the standard is highly pragmatic and addressed toward

commercial requirements.

What is SCSI

SCSI Initiator: An endpoint that initiates a SCSI session, that is, sends a SCSI

command.

SCSI Target: Usually a disk or a storage array.

SCSI LUN: SCSI Logical Unit Number, the “real storage”, a SCSI target should

have at least one LUN: LUN0.

In SCSI terminology, communication takes place between an initiator and a

target. The initiator sends a command to the LUN, which then responds. SCSI

commands are sent in a Command Descriptor Block (CDB).

What is SCSI

Lsscsi shows [Host:Bus:Target:LUN], device type,

vendor, etc

lsscsi shows SATA devices, Because SATA uses SCSI

transport layer.

What is SCSI

What is iSCSI

What is iSCSI

Carry SCSI CBD in iSCSI PDU, benefit from IP networks.

Key words in iSCSI:

• ISID: The initiator part of the Session Identifier. It is explicitly specified by

the initiator during Login.

• I_T nexus: According to [SAM2], the I_T nexus is a relationship between a

SCSI Initiator Port and a SCSI Target Port.

• SSID (Session ID): A session between an iSCSI initiator and an iSCSI target

is defined by a session ID that is a tuple composed of an initiator part (ISID)

and a target part (Target Portal Group Tag). The ISID is explicitly specified by

the initiator at session establishment. The Target Portal Group Tag is implied

by the initiator through the selection of the TCP endpoint at connection

establishment.

What is iSCSI, key words:

• TSIH (Target Session Identifying Handle): A target assigned tag for a session

with a specific named initiator. The target generates it during session

establishment. Its internal format and content are not defined by this protocol,

except for the value 0 that is reserved and used by the initiator to indicate a

new session.

• ITT(Initiator Task Tag):The Initiator Task Tag is used to identify a task during

its execution even over sessions/connections.

• CID: connection ID.

• CmdSN: command sequence number.

• ExpStatSN: The expected status number, ExpStatSN is what the initiator uses

to tell the target what status response it thinks is the next one.

What is iSCSI, key words:

• StatSN:status sequence number, it is different from status also in the PDU.

Responses in transit from the target to the initiator are numbered. The StatSN

(Status Sequence Number) is used for this purpose. This helps the initiator

detect any missing StatSN(s) and issue a SNACK for the status

• ExpCmdSN: Next expected CmdSN from this initiator.

• MaxCmdSN: Maximum CmdSN from this initiator

iSCSI discovery 1/4:

iSCSI discovery 2/4:

iSCSI discovery 3/4:

iSCSI discovery 4/4:

How iSCSI carry SCSI commands

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Yast iSCSI target usage: discovery

Yast iSCSI target usage: add a target

Yast iSCSI target usage: add an initiaitor

Yast iSCSI target usage: login authentication

Yast iSCSI target usage: LUNs mapping

Targetcli overview

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Targetcli create backend storage

• Create a backend storage with a existed file:

backstores/fileio create name=iscsi_file file_or_dev=/home/lszhu/target.raw

• Create a backend storage with a file not existed, while you want to create the

file at the same time.

backstores/fileio create name=iscsi_file file_or_dev=/home/lszhu/target.raw

size=100M

• Create a backend storage with a block device

backstores/block/ create name=iscsi_sbc dev=/dev/sdc

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Targetcli create targets

/> iscsi/ create iqn.2017-03.suse.com.target

Created target iqn.2017-03.suse.com.target.

Created TPG 1.

Global pref auto_add_default_portal=true

Created default portal listening on all IPs (0.0.0.0), port 3260.

/>

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Targetcli create portals and luns

• Create a portal

/iscsi/iqn.20...m.target/tpg1> portals/ create ip_address=147.2.212.166

ip_port=3260

• Create a lun:

/iscsi/iqn.20...m.target/tpg1> luns/ create /backstores/block/iscsi_sdc

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Targetcli set demo mode

• Set to demo mode then every initiator can access the target without

authentication

/iscsi/iqn.20...m.target/tpg1> set attribute authentication=0

demo_mode_write_protect=0 generate_node_acls=1 cache_dynamic_acls=1

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Targetcli add an ACL

An ACL means you want some specific initiators granted the access to the targets,

others not.

1. /iscsi/iqn.20...m.target/tpg1> acls/ create iqn.2017-03.suse.com.lszhu.init

2. /iscsi/iqn.20...m.target/tpg1> cd acls/iqn.2017-03.suse.com.lszhu.init

3. /iscsi/iqn.20...om.lszhu.init> set auth userid=lszhu password=lszhu

mutual_userid=test mutual_password=test

4. /iscsi/iqn.20...om.lszhu.init> create mapped_lun=6

tpg_lun_or_backstore=lun0

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Q&A

Thanks