Linux-IO Storage Configuration - ISCSI -En Oracle Linux 7

Linux-IO Storage Configuration

Oracle Linux 7 with both UEK R3 and RHCK uses the Linux-IO Target (LIO) to provide the block-storage SCSI target for FCoE, iSCSI, and Mellanox InfiniBand (iSER and SRP). You can manage LIO by using the targetcli shell provided in the targetcli package.
Fibre Channel over Ethernet (FCoE) encapsulates Fibre Channel packets in Ethernet frames, which allows them to be sent over Ethernet networks. To configure FCoE storage, you also need to install the fcoe-utils package, which provides the fcoemon service and the fcoeadm command.
The Internet Small Computer System Interface (iSCSI) is an IP-based standard for connecting storage devices. iSCSI encapsulates SCSI commands in IP network packets, which allows data transfer over long distances and sharing of storage by client systems. As iSCSI uses the existing IP infrastructure, it does not require the purchase and installation of fiber-optic cabling and interface adapters that are needed to implement Fibre Channel (FC) storage area networks.
A client system (iSCSI initiator) accesses the storage server (iSCSI target) over an IP network. To an iSCSI initiator, the storage appears to be locally attached.
An iSCSI target is typically a dedicated, network-connected storage device but it can also be a general-purpose computer.
Figure 16.1 shows a simple network where several iSCSI initiators are able to access the shared storage that is attached to an iSCSI target.

Figure 16.1 iSCSI Initiators and an iSCSI Target Connected via an IP-based Network

The diagram shows a simple Ethernet network where several iSCSI initiators are able to access the shared storage that is attached to an iSCSI target.

A hardware-based iSCSI initiator uses a dedicated iSCSI HBA. Oracle Linux supports iSCSI initiator functionality in software. The kernel-resident device driver uses the existing network interface card (NIC) and network stack to emulate a hardware iSCSI initiator. As the iSCSI initiator functionality is not available at the level of the system BIOS, you cannot boot an Oracle Linux system from iSCSI storage .
To improve performance, some network cards implement TCP/IP Offload Engines (TOE) that can create a TCP frame for the iSCSI packet in hardware. Oracle Linux does not support TOE, although suitable drivers may be available directly from some card vendors.
For more information about LIO, see http://linux-iscsi.org/wiki/Main_Page.

16.6.1 Configuring an iSCSI Target

To set up a simple iSCSI target on an Oracle Linux system:

Run the targetcli shell:

# targetcli
targetcli shell version 2.1.fb31
Copyright 2011-2013 by Datera, Inc and others.
For help on commands, type 'help'.

List the object hierarchy, which is initially empty:

/> ls
o- / ..................................................................... [...]
  o- backstores .......................................................... [...]
  | o- block .............................................. [Storage Objects: 0]
  | o- fileio ............................................. [Storage Objects: 0]
  | o- pscsi .............................................. [Storage Objects: 0]
  | o- ramdisk ............................................ [Storage Objects: 0]
  o- iscsi ........................................................ [Targets: 0]
  o- loopback ..................................................... [Targets: 0]

Change to the /backstores/block directory and create a block storage object for the disk partitions that you want to provide as LUNs, for example:

/> cd /backstores/block
/backstores/block> create name=LUN_0 dev=/dev/sdb
Created block storage object LUN_0 using /dev/sdb.
/backstores/block> create name=LUN_1 dev=/dev/sdc
Created block storage object LUN_1 using /dev/sdc.

The names that you assign to the storage objects are arbitrary.

Change to the /iscsi directory and create an iSCSI target:

/> cd /iscsi
/iscsi> create
Created target iqn.2013-01.com.mydom.host01.x8664:sn.ef8e14f87344.
Created TPG 1.

List the target portal group (TPG) hierarchy, which is initially empty:

/iscsi> ls
o- iscsi .......................................................... [Targets: 1]
  o- iqn.2013-01.com.mydom.host01.x8664:sn.ef8e14f87344 .............. [TPGs: 1]
    o- tpg1 ............................................. [no-gen-acls, no-auth]
      o- acls ........................................................ [ACLs: 0]
      o- luns ........................................................ [LUNs: 0]
      o- portals .................................................. [Portals: 0]

Change to the luns subdirectory of the TPG directory hierarchy and add the LUNs to the target portal group:

/iscsi> cd iqn.2013-01.com.mydom.host01.x8664:sn.ef8e14f87344/tpg1/luns 
/iscsi/iqn.20...344/tpg1/luns> create /backstores/block/LUN_0
Created LUN 0.
/iscsi/iqn.20...344/tpg1/luns> create /backstores/block/LUN_1
Created LUN 1.

Change to the portals subdirectory of the TPG directory hierarchy and specify the IP address and port of the iSCSI endpoint:

/iscsi/iqn.20...344/tpg1/luns> cd ../portals
/iscsi/iqn.20.../tpg1/portals> create 10.150.30.72 3260
Using default IP port 3260
Created network portal 10.150.30.72:3260.

If you omit the port number, the default value is 3260.
List the object hierarchy, which now shows the configured block storage objects and TPG:

/iscsi/iqn.20.../tpg1/portals> ls /
o- / ..................................................................... [...]
  o- backstores .......................................................... [...]
  | o- block .............................................. [Storage Objects: 1]
  | | o- LUN_0 ....................... [/dev/sdb (10.0GiB) write-thru activated]
  | | o- LUN_1 ....................... [/dev/sdc (10.0GiB) write-thru activated]
  | o- fileio ............................................. [Storage Objects: 0]
  | o- pscsi .............................................. [Storage Objects: 0]
  | o- ramdisk ............................................ [Storage Objects: 0]
  o- iscsi ........................................................ [Targets: 1]
  | o- iqn.2013-01.com.mydom.host01.x8664:sn.ef8e14f87344 ............ [TPGs: 1]
  |   o- tpg1 ........................................... [no-gen-acls, no-auth]
  |     o- acls ...................................................... [ACLs: 0]
  |     o- luns ...................................................... [LUNs: 1]
  |     | o- lun0 ..................................... [block/LUN_0 (/dev/sdb)]
  |     | o- lun1 ..................................... [block/LUN_1 (/dev/sdc)]
  |     o- portals ................................................ [Portals: 1]
  |       o- 10.150.30.72:3260 ............................................ [OK]
  o- loopback ..................................................... [Targets: 0]

Configure the access rights for logins by initiators. For example, to configure demonstration mode that does not require authentication, change to the TGP directory and set the values of the authentication and demo_mode_write_protect attributes to 0 and generate_node_acls cache_dynamic_acls to 1:
```
/iscsi/iqn.20.../tpg1/portals> cd ..
/iscsi/iqn.20...14f87344/tpg1> set attribute authentication=0 demo_mode_write_protect=0 \
generate_node_acls=1 cache_dynamic_acls=1
Parameter authentication is now '0'.
Parameter demo_mode_write_protect is now '0'.
Parameter generate_node_acls is now '1'.
Parameter cache_dynamic_acls is now '1'.
```
Caution
Demonstration mode is inherently insecure. For information about configuring secure authentication modes, see http://linux-iscsi.org/wiki/ISCSI#Define_access_rights.
Change to the root directory and save the configuration so that it persists across reboots of the system:
```
/iscsi/iqn.20...14f87344/tpg1> cd /
/> saveconfig
Last 10 configs saved in /etc/target/backup.
Configuration saved to /etc/target/saveconfig.json
```
targetcli saves the current configuration to the JSON-format file /etc/target/saveconfig.json.

For more information, see the targetcli(8) manual page.

16.6.2 Configuring an iSCSI Initiator

To configure an Oracle Linux system as an iSCSI initiator:

Install the iscsi-initiator-utils package:
```
# yum install iscsi-initiator-utils
```

Use the SendTargets discovery method to discover the iSCSI targets at a specified IP address:

# iscsiadm -m discovery -t sendtargets -p 10.150.30.72
10.150.30.72:3260,1 iqn.2013-01.com.mydom.host01.x8664:sn.ef8e14f87344

Note

An alternate discovery method is Internet Storage Name Service (iSNS).

The command also starts the iscsid service if it is not already running.
The following command displays information about the targets that is now stored in the discovery database:

# iscsiadm -m discoverydb –t st –p 10.150.30.72
# BEGIN RECORD 6.2.0.873-14
discovery.startup = manual
discovery.type = sendtargets
discovery.sendtargets.address = 10.150.30.72
discovery.sendtargets.port = 3260
discovery.sendtargets.auth.authmethod = None
discovery.sendtargets.auth.username = <empty>
discovery.sendtargets.auth.password = <empty>
discovery.sendtargets.auth.username_in = <empty>
discovery.sendtargets.auth.password_in = <empty>
discovery.sendtargets.timeo.login_timeout = 15
discovery.sendtargets.use_discoveryd = No
discovery.sendtargets.discoveryd_poll_inval = 30
discovery.sendtargets.reopen_max = 5
discovery.sendtargets.timeo.auth_timeout = 45
discovery.sendtargets.timeo.active_timeout = 30
discovery.sendtargets.iscsi.MaxRecvDataSegmentLength = 32768
# END RECORD

Establish a session and log in to a specific target:

# iscsiadm -m node -T iqn.2013-01.com.mydom.host01.x8664:sn.ef8e14f87344 \
  –p 10.150.30.72:3260 -l
Login to [iface: default, target: iqn.2003-01.org.linux-iscsi.localhost.x8664:
sn.ef8e14f87344, portal: 10.150.30.72,3260] successful.

Verify that the session is active, and display the available LUNs:

# iscsiadm -m session –P 3
iSCSI Transport Class version 2.0-870
version 6.2.0.873-14
Target: iqn.2003-01.com.mydom.host01.x8664:sn.ef8e14f87344 (non-flash)
 Current Portal: 10.0.0.2:3260,1
 Persistent Portal: 10.0.0.2:3260,1
  **********
  Interface:
  **********
  Iface Name: default
  Iface Transport: tcp
  Iface Initiatorname: iqn.1994-05.com.mydom:ed7021225d52
  Iface IPaddress: 10.0.0.2
  Iface HWaddress: <empty>
  Iface Netdev: <empty>
  SID: 5
  iSCSI Connection State: LOGGED IN
  iSCSI Session State: LOGGED_IN
  Internal iscsid Session State: NO CHANGE
.
.
.
  ************************
  Attached SCSI devices:
  ************************
  Host Number: 8 State: running
  scsi8 Channel 00 Id 0 Lun: 0
   Attached scsi disk sdb  State: running
  scsi8 Channel 00 Id 0 Lun: 1
   Attached scsi disk sdc  State: running

The LUNs are represented as SCSI block devices (sd*) in the local /dev directory, for example:

# fdisk –l | grep /dev/sd[bc]
Disk /dev/sdb: 10.7 GB, 10737418240 bytes, 20971520 sectors
Disk /dev/sdc: 10.7 GB, 10737418240 bytes, 20971520 sectors

To distinguish between target LUNs, examine their paths under /dev/disk/by-path:

# ls -l /dev/disk/by-path/
lrwxrwxrwx  1 root root  9 May 15 21:05
  ip-10.150.30.72:3260-iscsi-iqn.2013-01.com.mydom.host01.x8664:
  sn.ef8e14f87344-lun-0 -> ../../sdb
lrwxrwxrwx 1 root root  9 May 15 21:05
  ip-10.150.30.72:3260-iscsi-iqn.2013-01.com.mydom.host01.x8664:
  sn.ef8e14f87344-lun-1 -> ../../sdc

You can view the initialization messages for the LUNs in the /var/log/messages file, for example:

# grep sdb /var/log/messages
...
May 18 14:19:36 localhost kernel: [12079.963376] sd 8:0:0:0: [sdb] Attached SCSI disk
...

You can configure and use a LUN in the same way as you would any other physical storage device. For example, you can configure it as an LVM physical volume, file system, swap partition, Automatic Storage Management (ASM) disk, or raw device.
Specify the _netdev option when creating mount entries for iSCSI LUNs in /etc/fstab, for example:

UUID=084591f8-6b8b-c857-f002-ecf8a3b387f3     /iscsi_mount_point     ext4     _netdev   0  0

This option indicates the file system resides on a device that requires network access, and prevents the system from attempting to mount the file system until the network has been enabled.

Note

Specify an iSCSI LUN in /etc/fstab by using UUID=UUID rather than the device path. A device path can change after re-connecting the storage or rebooting the system. You can use the blkid command to display the UUID of a block device.
Any discovered LUNs remain available across reboots provided that the target continues to serve those LUNs and you do not log the system off the target.

For more information, see the iscsiadm(8) and iscsid(8) manual pages.

16.6.3 Updating the Discovery Database

If the LUNs that are available on an iSCSI target change, you can use the iscsiadm command on an iSCSI initiator to update the entries in its discovery database. The following example assume that the target supports the SendTargets discovery method
To add new records that are not currently in the database:

# iscsiadm --mode discoverydb –type st –p 10.150.30.72 –o new --discover

To update existing records in the database:

# iscsiadm -m discoverydb –t st –p 10.150.30.72 –o update --discover

To delete records from the database that are no longer supported by the target:

# iscsiadm -m discoverydb –t st –p 10.150.30.72 –o delete --discover

For more information, see the iscsiadm(8) manual page.

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