What is iscsi in linux

What is iscsi in linux

Before we define iSCSI,we must know what is SCSI itself.

SCSI: Small Computer Systems Interface, i s a family of protocols for communicating with I/O devices( especially storage).

SCSI protocol is being used by servers to communicate with storages over various types of transports like SAS , SAS2 ,SATA, Parallel SSCSI , FC…etc.

for SAS or SATA we have the limitation in the distance that these cables support,while in Fibre Channel (FC) it can go for long distances ,but it is very costly.

1- SCSI is a client-server architecture, client is “initiator” while storage is “target”

2- initiator mostly is OS ( Windows, Linux, Unix) . Target mostly is storage like (NetApp,EMC,ZFS..etc ).

So, SCSI packets is being transported mostly by SAS ,SATA,and FC cables.

iSCSI : is transporting SCSI packets over TCP/IP, providing block-level access to storage devices over TCP/IP network.

So, initiators will have its own IP and targets as well ,all packets are being transported over normal IP networks

Initiators issue SCSI “commands” to request services from targets.

But how initiator(operating system ) can discover targets (storag)?

iSCSI discovery mechanism:

1- Send Targets : the target IP and Port is known to the initiator, a discovery session is established , then initiator sends SendTargets commands to get available iscsi targets from storage.

2- Static Configuration: the IP,Port and IQN of target are available for the initiator.

3- Zero-Configuration : the initiator doesn’t have any information about targets, a discovery messages are sent to Storage Name Server ( iSNS , SLP…etc), where all information regarding initiators and targets and access list.

iSNS: Internet Storage Name Server , is centeralized server that has iSCSI configurations of initiators and targets.

SLP : Service Location Protocol, is not widely implemented, but anyway it helps computers to find iSCSI services across network.

in iSCSI network, each component (initiator or target ) has its unique name,Lets have a look at naming types

iSCSI Naming: Three naming are supported by iSCSI

1- iqn ( iSCSI Qualified Name )format : iqn.yyyy-mm.ReversedDomain:String

2- eui :eui. (e.g. eui.02004567A425678D)

3- NAA Network Address Authority: naa. (e.g. naa.52004567BA64678D)

SCSI Transport Protocol	EUI-64	NAA	IQN
iSCSI	X	X	X
FCP ( Fibre Channel)	X
SAS	X

the initiator and target, both creates a session for communication as following

1- Discovery Session: opened to discover target only

2- Normal Operation Session: unrestricted session for I/O operations

iSCSI supports two separate security mechanisms:

1-in-band authentication between initiator and target at the iSCSI connection level.(like CHAP authentication), occurs during login into storage

2- packet protection by IPsec at the IP level.( all packets are secured )

iSCSI will do a login to storgae first(here we implement in-band authentication if needed ),after successfull login it will start exchanging packets ( here we can implement IPSec if needed)

Lets see how to configure Solaris and Linux as a client fro storages :

1- Solaris Configuration as a client to connect to iSCSI storage:

Assuming Storage IP is 10.10.10.151

Here is the sequence of commands to use:

# svcadm enable network/iscsi/initiator

# iscsiadm modify discovery –static enable

# iscsiadm modify discovery –sendtargets enable

# iscsiadm add discovery-address 10.10.10.151

# iscsiadm list discovery-address -v 10.10.10.151 (get iqn of target and use in next command)

# iscsiadm add static-config iqn.1986-03.com.sun:02:1859adc5-0f56-c7a4-a08a-dfad6332b09a,10.10.10.151

#iscsiadm list target -vS ( list iscsi devices and OS disk path)

2- Linux 7 Configuration as a client to connect to iSCSI storage:

# systemctl start iscsi iscsid ( enable iscsi daemon )

# cat /etc/iscsi/initiatorname.iscsi ( get you host iqn ,share it with storage admin)

# iscsiadm -m discovery -t sendtargets -p 10.10.10.151 ( query iqn of target ,it will be used in next command )

# iscsiadm -m node -T iqn.1986-03.com.sun:02:1859adc5-0f56-c7a4-a08a-dfad6332b09a -p 10.10.10.151 –login

# iscsiadm -m node -o update -n node.startup -v automatic ( enable auto startup )

# iscsiadm -m node -o update -n node.conn[0].startup -v automatic ( enable auto connection startup )

# iscsiadm –mode node -l all ( create all needed devices )

# iscsiadm -m session -P 2

# add line in /etc/fstab ,like: ( be sure you add _netdev ,it tells kernel the device is network device ,otherwise linux wll run into single user-mode if you reboot the machine )

/dev/sdb1 /ahmed xfs defaults,_netdev 0 0

1- RFC 3721 , 7143 (IETF Internet Engineering Task Force)

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How to Install and Configure iSCSI Storage Server on CentOS

For RHEL/CentOS 6/7 systems, use the yum command to install sg3_utils. For RHEL/CentOS 8 and Fedora systems, use the dnf command to install sg3_utils. New LUN’s can be scanned using the rescan-scsi-bus.sh script as follows.

How do I connect to iSCSI?

1. Open the iSCSI Initiator Properties dialog box: .
2. On the Discovery tab, click Discover Portal or Add Portal, and then enter the IP address of the iSCSI target port.
3. On the Targets tab, select the target you discovered, and then click Log on or Connect.

What is iSCSI in Linux?

Internet SCSI (iSCSI) is a network protocol s that allows you to use of the SCSI protocol over TCP/IP networks. It is good alternative to Fibre Channel-based SANs. You can easily manage, mount and format iSCSI Volume under Linux. It allows access to SAN storage over Ethernet.

Is iSCSI faster than NFS?

Neither iSCSI nor NFS is inherently faster (they have similar overheads, etc). But certainly some arrays are better at block or NFS than others. Same with host initiators.

Is iSCSI faster than SMB?

Windows SMB/CIFS network shares may be slightly faster than iSCSI for large file transfers. The opposite may be true for small file copies. Many variables such as source and target hardware may impact the performance, so your results may vary.

Do I need iSCSI initiator?

The need for a NIC-based TCP/IP offload engine (TOE) has declined as servers have gained more powerful processing cores. A hardware iSCSI initiator may still be useful for data protection, when booting a server from a local disk, or for security, if the card has built-in encryption capabilities.

How do I find my iSCSI IP address in Linux?

Determine the iSCSI port names using the # ifconfig -a command. Set the IP address for the iSCSI initiator ports. The initiator ports should be present on the same subnet as the iSCSI target ports. Note: Be sure to set the address for both iSCSI initiator ports.

How configure iSCSI LUN?

1. On the Local adapter list, select Microsoft® iSCSI Initiator.
2. On the Initiator IP list, select the IP address of the host.
3. On the Target Portal IP list, select the IP of one of the storage interfaces.
4. Click Enable CHAP log-on check box.

Where is iSCSI disk in Linux?

1. Enter the following command to discover the iSCSI target: iscsiadm —mode discovery —op update —type sendtargets —portal targetIP. .
2. Enter the following command to create all needed devices: iscsiadm —mode node -l all. .
3. Enter the following command to see all the active iSCSI sessions: iscsiadm —mode session.

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