A slide show for Linuxfest Northwest 2019. Using openSUSE/SLES as an example, this shows how to set up targets (disc and tape) and initiators, and touches on some advanced subjects.

1. Lee Duncan
SUSE Labs iSCSI Hacker
lduncan@suse.com
Using iSCSI to share Disc and Tape
SAN for Dummies (or non-SAN Administrators)

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Learning about iSCSI on Linux
● My Background
– SCSI and iSCSI experience
– Worked for SUN, HP, GE, AT&T, now SUSE
– Co-maintainer of open-iscsi initiator
– Co-maintainer of Linux kernel initiator code
– Maintainer of targets and initiator for SUSE
– Other github projects (gonzoleeman)

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Learning about iSCSI on Linux
● Talking about today:
– What is iSCSI?
– What is the value of iSCSI?
– iSCSI Basics: Initiators, Targets, and Sessions
– iSCSI Tape
– iSCSI Services and systemd
– Advanced iSCSI topics
● iSNS, tcmu-runner, ...

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What is iSCSI?
● iSCSI is just SCSI over a transport, e.g. TCP/IP
– RFC3270: Initial IETF Request for Comment
– RFC3721/RFC3980/etc: Naming, etc
– RFC7143/RFC7144: Updates/replaces 3270 and friends
– Encapsulates SCSI commands and responses for
transport
● We get remote storage using non-storage transport

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What is SCSI?
● SCSI is just a way that a computer and disc can talk
– The Computer makes requests: this client initiates all
communication
– The Disc responds: it’s target serves disc data to the
computer
– All modern SCSI Discs and Tape speak SCSI-2/SCSI-3
● ATA is a subset of SCSI

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What is the Value of iSCSI?
● Free and open software
● Cheap: you do not need special hardware, other than
your network
● Well used: it is generally reliable/mature
● Well maintained
– New stuff still being added (e.g. tcmu_runner)
● Can be building block for larger storage systems

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iSCSI Basics: Initiators, Targets and Sessions
● iSCSi uses initiators, targets, and sessions
● Initiators and Targets have unique names
– iSCSI Qualified Name
● iqn.YYYY-MM.name-athority:unique-name
● A Session is an Initiator/Target connection
– Logs on, Logs off
● Packages to use:
– Use open-iscsi for our initiator (client)
– Use targetcli-fb for our target (server)

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iSCSI Basics: Topology (simple)
NetworkNetwork
Client*Client*
ServerServer
iSCSI InitiatoriSCSI Initiator
iSCSI TargetiSCSI Target
LULU
open-iscsi
targetcli-fb/LIO
iqn.yyyy-mm.name-authority:unique-name
iqn.yyyy-mm.name-authority:unique-name
Storage (or Tape)
Switch

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iSCSI Basics: Setting up the Target
● We need a target for the initiator to connect to
– Can be disc, partition, file, SCSI device, ...
● Things we care about for our target:
– Storage Where’s the bits?
– Name An IQN
– Access ACL, Location

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iSCSI Basics: Setting up the Target (cont)
● Two parts to a target (must be connected)
– Backstore
● Where the bits actually live
● Several different types (file, disc, tape, ...)
– Target front-end
● Our Name iqn.*
● Portal(s) Address(es) (IP:Port)
● LU(s) Points to backstore
● ACL(s) Initiator IQN(s)

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iSCSI Basics: Setting up the Target (cont)
● Let’s use the targetcli(1) command to configure out
target
– Use the “free branch” version
– Can be interactive or batch mode
– Must be root
– Shell-like
● Has a node hierarchy: root, directories, ...
● Commands depend on where you are in tree

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iSCSI Basics: Setting up the Target (cont)
iscsi vhost
/
loopbackbackstores xen-pvscsi
block fileio pscsi ramdisc rbd
An empty
targetcli tree
tcm_loop for kvm
guests
XEN
ParaVirt
SCSI

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iSCSI Basics: Setting up the Target (cont)
So how does that look on the command line?
Let’s look at an empty target subsystem …

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iSCSI Basics: Setting up the Target (cont)

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iSCSI Basics: Setting up the Target (cont)
● Let’s create the backstore first
● Use fileio – Size 10M
– Use backstore directory /alt/bs/
– Use/create backstore file bs.img
● Let’s let targetcli create the backstore
– It defaults to sparse files

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iSCSI Basics: Setting up the Target (cont)
● Then we will create the front-end
– We want the iscsi front end
– We will pick our own IQN (iscsi target name)
– We will allow connection from any initiator
– We will allow connection from any portal

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iSCSI Basics: Setting up the Target (cont)

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iSCSI Basics: Setting up the Target (cont)

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iSCSI Basics: Setting up the Target (cont)
Let’s look at what we created …
Then we will finish configuring the front end

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iSCSI Basics: Setting up the Target (cont)

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iSCSI Basics: Setting up the Target (cont)

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iSCSI Basics: Setting up the Target (cont)
● Now to configure the front end
– Set iSCSI attribute for demo mode
– Set iSCSI attribute for read-write demo mode
– Then create our Logical Unit (LU)
● The connect to the backend

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iSCSI Basics: Setting up the Target (cont)

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iSCSI Basics: Setting up the Target (cont)

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iSCSI Basics: Setting up the Target (cont)

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iSCSI Basics: Setting up the Target (cont)

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iSCSI Basics: Setting up the Target (cont)

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iSCSI Basics: Setting up the Target (cont)
Finally, let’s look at the result!

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iSCSI Basics: Setting up the Target (cont)

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iSCSI Basics: Setting up the Initiator
Now that we have a target disc, how to use it?
Perhaps we need an initiator

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iSCSI Basics: Setting up the Initiator
● The initiator uses the open-iscsi package
– Installed and enabled by default
● Can be configured using
– Command line: iscsiadm(1)

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iSCSI Basics: Setting up the Initiator (cont)
● Initiator uses two phases to connect:
– Discovery: find target(s) at IP:Port
– Login: connect to discovered target(s)
● Creates Sessions
● Command line
– iscsiadm(1)

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iSCSI Basics: Setting up the Initiator (cont)
● Using iscsiadm(1)
– First, we will enter the Discovery phase
– We will use the iSCSI protocol command SendTargets
– We will build up a database of Nodes found
– We can then use that database to establish session(s)

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iSCSI Basics: Setting up the Initiator (cont)

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iSCSI Basics: Setting up the Initiator (cont)

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iSCSI Basics: Setting up the Initiator (cont)

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iSCSI Basics: Setting up the Initiator (cont)

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iSCSI Basics: Setting up the Initiator (cont)

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iSCSI Basics: Setting up the Initiator (cont)

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iSCSI Basics: Setting up the Initiator (cont)

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iSCSI Basics: Setting up the Initiator (cont)

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iSCSI Basics: Setting up the Initiator (cont)

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iSCSI Basics: Setting up the Initiator (cont)

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iSCSI Basics: Setting up the Initiator (cont)

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iSCSI: Sharing a Tape Drive
● Very similar to sharing a disc
● We use pscsi (Pass-through SCSI) back-end
● The front-end stays the same
● We will set up the tape Target, then the Initiator

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iSCSI Tape: Setting up the Target

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iSCSI Tape: Setting up the Target (cont)

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iSCSI Tape: Setting up the Target (cont)

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iSCSI Tape: Setting up the Target (cont)

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iSCSI Tape: Setting up the Target (cont)

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iSCSI Tape: Setting up the Target (cont)

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iSCSI: Sharing a Tape Drive (cont)
● Now the Target is Set Up
● Let’s set up the Initiator
– Just like before, but on different host (no tape drive)

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iSCSI Tape: Setting up the Initiator

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iSCSI Tape: Setting up the Initiator (cont)

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iSCSI Tape: Setting up the Initiator (cont)

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iSCSI Tape: Setting up the Initiator (cont)

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iSCSI Tape: Setting up the Initiator (cont)

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iSCSI Services: Using systemd
● These days you have to understand/use systemd
● Systemd manages services
– iSCSI initiator Service(s)
– iSCSI target Service(s)
● Examples based on SUSE Linux
– other distros similar

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iSCSI Services: Using systemd (cont)
● Target (targetcli-fb) uses targetcli.service
● Does not really control a daemon
● Mostly just manages storing/recovering state

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iSCSI Services: Using systemd (cont)

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iSCSI Services: Using systemd (cont)
● Initiator uses three services
– The iscsid service manages the daemon
– The iscsi service manages sessions
● requires iscsid service
– The iscsiuio service manages CNA daemon
● For some Hardware-assisted iSCSI adapters
– The two daemon services are socket-activated
● This starts the service automatically, when needed!

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iSCSI Services: Using systemd (cont)

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iSCSI Services: Using systemd (cont)

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iSCSI Services: Using systemd (cont)
● Initiator has to modify the node database
– Only needed if we wish connection to persist across reboots
– Set the node connection startup value to automatic

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iSCSI Services: Using systemd (cont)

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iSCSI Services: Using systemd (cont)

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iSCSI Services: Using systemd (cont)

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iSCSI Services: Using systemd (cont)

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iSCSI: Advanced Topics
● Now that we have the basics down, what else is there?
– Access Control/Security
– iSNS – the iSCSI Directory Service
– YaST (mentioned for reference)
– tcmu-runner

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iSCSI: Advanced Topics (cont)
● Access Controls (i.e. security?)
– Different types
● Access (ACLs)
● Discovery
● Session/Login
– ACLs: Can control which IQNs (initiators) connect
– Discovery: Can set name/password for each target
– Session: Can set name/password for each target
● MUST be different than the Discovery set!
– Assumes a secure network!

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iSCSI: Advanced Topics (cont)
●
iSNS: iSCSI Directory Services
– See RFC 4171
– Answers the question: how do I find my iSCSI Storage
– Also provices Asynch Notification!
– Replaces need for knowing IQN and IP of target
– Now you just need IP/name of iSNS server
– Targets and Initiators register
– Initiators query to find Targets
– Uses open-isns and target-isns packages

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iSCSI: Advanced Topics (cont)
● What is tcmu-runner?
– TCM is another name for LIO
– tcm-user is another back end
– tcm-runner runs plugs in userspace
● Let’s look at the LIO/TCM Linux Target Architecture
– But just a tease ...

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iSCSI: Advanced Topics (cont)
vhost
loopback
iscsi
targetcli
Initiator
fileIO
block
pscsi
ramdisc
tcm-user
tcmu-runner
qcow2 qlfs
user
kernel
LIO Core

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iSCSI: That’s It!
● iSCSI is easy to set up on Linux
● Don’t be afraid of the command line
● You can roll your own SAN!

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iSCSI: For More Information
● https://www.open-iscsi.com
● https://github.com/open-iscsi/targetcli-fb
● https://github.com/open-iscsi/open-isns
● https://github.com/open-iscsi/target-isns
● https://github.com/open-iscsi/tcmu-runner
● https://build.opensuse.org – Open Build Service
● https://www.slideshare.net/LeeDuncan16/using-iscsi-lfnw

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● Contact:
lduncan@suse.com

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Credits
Template
Richard Brown
rbrown@opensuse.org
Design & Inspiration
openSUSE Design Team
http://opensuse.github.io/branding-guidelines/
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