iSCSI:
internet SCSI(iSCSI):iSCSI主要是通过TCP/IP 的技术，将存储设备通过iSCSI target(iSCSI标的)功能，做成可以提供磁盘的服务器端，再通过iSCSI initiator(iSCSI 初始化用户)功能，做成能够挂载使用iSCSI target的客户端，如此便能通过iSCSI协议来进行磁盘的应用了。
iSCSI 是IETF制定的一项标准，它是一个供硬件设备使用的可以在IP协议的上层运行的SCSI指令集，这种指令集和
用于将SCSI数据块映射为以太网数据包，以此来实现在IP网络上运行SCSI协议，使其能够在诸如高速千兆以太网上进行路由选择.
从根本上说，iSCSI是一种基于IP Storage理论的新型存储技术，该技术将广泛使用的SCSI接口技术与IP网络技术相结合，可以在IP
网络上构建SAN。简单的说，iSCSI就是在IP网络上运行SCSI协议的一种网络存储技术。
iSCSI这个架构主要将存储设备与使用的主机分为俩个部分，分别是:
iSCSI target:就是存储设备端，存放磁盘RAID的设备，目前也能够将Linux主机仿真成iSCSI target,目的在于提供其他主机使用的磁盘。
iSCSI initiator：就是能够使用target的客户端，通常是服务器,想要连接到iSCSI target的服务器，也必须要安装iSCSI initiator的相关功能后才能使用iSCSI target提供的磁盘。
iSCSI的优势:
iSCSI沿用TCP/IP协议，而TCP/IP是在网络方面最通用、最成熟的协议，且IP网络的基础建非常完善，同时SCSI技术是被磁盘和磁带等设备
广泛采用的存储标准，这俩点是iSCSI的建设费用和维护成本非常低廉。
iSCSI支持一般的以太网交换机而不是特殊的光线通道交换机，从而减少了异构网络带来的风险。
iSCSI是通过IP封包传输存储命令，因此可以在整个Internet上传输数据，没有距离的限制。
iSCSI target(iSCSI标的)设置:(也就是服务端)
所需程序:RHEL7使用targetcli,targetd(RHEL6使用:scsi-target-utils(tgt) )
启动targetcli
systemctl start target
iSCSI target(iSCSI标的)的实际设置:
iSCSI就是通过一个网络接口，将既有的磁盘共享出去。
那么那些类型的磁盘可以共享呢，这包括:
使用dd命令所建立的大型文件可供仿真为磁盘(无须预先格式化)
使用单一分区(partition)共享为磁盘
使用单一完整的磁盘(无须预先分区)
使用磁盘整列共享(其实与单一磁盘相同方式)
使用软件磁盘阵列(software RAID)共享成单一磁盘
使用LVM的LV设备共享为磁盘ISCSI服务端配置:
ISCSI配置范例:(使用硬盘做存储端)
iSCSI target(iSCSI标的)的配置:(服务器端ip:192.168.1.118)
1.创建2个4GB的分区/dev/sdb1,/dev/sdb1
2. yum install target* -y
3. systemctl start target ; systemctl enable target
targetcli是用于管理iSCSI服务端存储的资源的专用配置命令,它能够提供类似于fdsik命令的交互式配置功能，
将iSCSI共享资源的配置内容抽象成"目录"的形式，我们只需将各类配置信息填入到相应的"目录"中既可。
/backstores/block是iSCSI服务端配置共享设备的位置。
4.进入target子系统:
[root@localhost ~]# targetcli
Warning: Could not load preferences file /root/.targetcli/prefs.bin.
targetcli shell version 2.1.fb37
Copyright 2011-2013 by Datera, Inc and others.
For help on commands, type 'help'.
/>
5. 创建block1,block2,分别对应/dev/sdb1,/dev/sdb2
[root@localhost ~]# targetcli
Warning: Could not load preferences file /root/.targetcli/prefs.bin.
targetcli shell version 2.1.fb37
Copyright 2011-2013 by Datera, Inc and others.
For help on commands, type 'help'.
/> 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]
/> /backstores/block create block1 /dev/sdb1
Created block storage object block1 using /dev/sdb1.
/> ls
o- / ......................................................................................................................... [...]
o- backstores .............................................................................................................. [...]
| o- block .................................................................................................. [Storage Objects: 1]
| | o- block1 ........................................................................ [/dev/sdb1 (3.7GiB) write-thru deactivated]
| o- fileio ................................................................................................. [Storage Objects: 0]
| o- pscsi .................................................................................................. [Storage Objects: 0]
| o- ramdisk ................................................................................................ [Storage Objects: 0]
o- iscsi ............................................................................................................ [Targets: 0]
o- loopback ......................................................................................................... [Targets: 0]
/> /backstores/block create block2 /dev/sdb2
Created block storage object block2 using /dev/sdb2.
/> ls
o- / ......................................................................................................................... [...]
o- backstores .............................................................................................................. [...]
| o- block .................................................................................................. [Storage Objects: 2]
| | o- block1 ........................................................................ [/dev/sdb1 (3.7GiB) write-thru deactivated]
| | o- block2 ........................................................................ [/dev/sdb2 (3.7GiB) write-thru deactivated]
| o- fileio ................................................................................................. [Storage Objects: 0]
| o- pscsi .................................................................................................. [Storage Objects: 0]
| o- ramdisk ................................................................................................ [Storage Objects: 0]
o- iscsi ............................................................................................................ [Targets: 0]
o- loopback ......................................................................................................... [Targets: 0]
/>
6. 创建target iqn.2019-04.com.test.www:disk
/> /iscsi create iqn.2019-04.com.test.www:disk
Created target iqn.2019-04.com.test.www:disk.
Created TPG 1.
Global pref auto_add_default_portal=true
Created default portal listening on all IPs (0.0.0.0), port 3260.
/>
/> ls
o- / ......................................................................................................................... [...]
o- backstores .............................................................................................................. [...]
| o- block .................................................................................................. [Storage Objects: 2]
| | o- block1 ........................................................................ [/dev/sdb1 (3.7GiB) write-thru deactivated]
| | o- block2 ........................................................................ [/dev/sdb2 (3.7GiB) write-thru deactivated]
| o- fileio ................................................................................................. [Storage Objects: 0]
| o- pscsi .................................................................................................. [Storage Objects: 0]
| o- ramdisk ................................................................................................ [Storage Objects: 0]
o- iscsi ............................................................................................................ [Targets: 1]
| o- iqn.2019-04.com.test.www:disk ..................................................................................... [TPGs: 1]
| o- tpg1 ............................................................................................... [no-gen-acls, no-auth]
| o- acls .......................................................................................................... [ACLs: 0]
| o- luns .......................................................................................................... [LUNs: 0]
| o- portals .................................................................................................... [Portals: 1]
| o- 0.0.0.0:3260 ..................................................................................................... [OK]
o- loopback ......................................................................................................... [Targets: 0]
/>
7.配置target iqn.2019-04.com.test.www:disk
(iSCSI协议是通过客户端名称进行验证的，也就是说用户在访问存储共享资源时不需要输入密码，只要iSCSI客户端的名称与服务端中
设置的访问控制列表中某一项名称条目既可，因此需要在iSCSI服务端的配置文件中写入一串能够验证用户信息的名称。acls参数目录用于存放能够访问iSCSI服务端共享存储资源的客户端名称)
/> cd /iscsi/iqn.2019-04.com.test.www:disk/tpg1/
/iscsi/iqn.20...www:disk/tpg1> ls
o- tpg1 ..................................................................................................... [no-gen-acls, no-auth]
o- acls ................................................................................................................ [ACLs: 0]
o- luns ................................................................................................................ [LUNs: 0]
o- portals .......................................................................................................... [Portals: 1]
o- 0.0.0.0:3260 ........................................................................................................... [OK]
/iscsi/iqn.20...www:disk/tpg1> acls/ create iqn.2019-04.com.test.www:xx (创建acls)
Created Node ACL for iqn.2019-04.com.test.www:xx
/iscsi/iqn.20...www:disk/tpg1> ls
o- tpg1 ..................................................................................................... [no-gen-acls, no-auth]
o- acls ................................................................................................................ [ACLs: 1]
| o- iqn.2019-04.com.test.www:xx ................................................................................ [Mapped LUNs: 0]
o- luns ................................................................................................................ [LUNs: 0]
o- portals .......................................................................................................... [Portals: 1]
o- 0.0.0.0:3260 ........................................................................................................... [OK]
/iscsi/iqn.20...www:disk/tpg1>
/iscsi/iqn.20...www:disk/tpg1> ls
o- tpg1 ..................................................................................................... [no-gen-acls, no-auth]
o- acls ................................................................................................................ [ACLs: 1]
| o- iqn.2019-04.com.test.www:xx ................................................................................ [Mapped LUNs: 0]
o- luns ................................................................................................................ [LUNs: 0]
o- portals .......................................................................................................... [Portals: 1]
o- 0.0.0.0:3260 ........................................................................................................... [OK]
/iscsi/iqn.20...www:disk/tpg1> luns/ create /backstores/block/block1
Created LUN 0.
Created LUN 0->0 mapping in node ACL iqn.2019-04.com.test.www:xx
/iscsi/iqn.20...www:disk/tpg1> luns/ create /backstores/block/block2 (使block与lun关联)
Created LUN 1.
Created LUN 1->1 mapping in node ACL iqn.2019-04.com.test.www:xx
/iscsi/iqn.20...www:disk/tpg1>
/iscsi/iqn.20...www:disk/tpg1> ls
o- tpg1 ..................................................................................................... [no-gen-acls, no-auth]
o- acls ................................................................................................................ [ACLs: 1]
| o- iqn.2019-04.com.test.www:xx ................................................................................ [Mapped LUNs: 2]
| o- mapped_lun0 ...................................................................................... [lun0 block/block1 (rw)]
| o- mapped_lun1 ...................................................................................... [lun1 block/block2 (rw)]
o- luns ................................................................................................................ [LUNs: 2]
| o- lun0 ............................................................................................. [block/block1 (/dev/sdb1)]
| o- lun1 ............................................................................................. [block/block2 (/dev/sdb2)]
o- portals .......................................................................................................... [Portals: 1]
o- 0.0.0.0:3260 ........................................................................................................... [OK]
/iscsi/iqn.20...www:disk/tpg1> ls
o- tpg1 ..................................................................................................... [no-gen-acls, no-auth]
o- acls ................................................................................................................ [ACLs: 1]
| o- iqn.2019-04.com.test.www:xx ................................................................................ [Mapped LUNs: 2]
| o- mapped_lun0 ...................................................................................... [lun0 block/block1 (rw)]
| o- mapped_lun1 ...................................................................................... [lun1 block/block2 (rw)]
o- luns ................................................................................................................ [LUNs: 2]
| o- lun0 ............................................................................................. [block/block1 (/dev/sdb1)]
| o- lun1 ............................................................................................. [block/block2 (/dev/sdb2)]
o- portals .......................................................................................................... [Portals: 1]
o- 0.0.0.0:3260 ........................................................................................................... [OK]
/iscsi/iqn.20...www:disk/tpg1> portals/ delete 0.0.0.0 3260 (删除默认的监听地址)
Deleted network portal 0.0.0.0:3260
/iscsi/iqn.20...www:disk/tpg1> portals/ create 192.168.1.118 3260 (创建新的监听地址)
Using default IP port 3260
Created network portal 192.168.1.118:3260.
/iscsi/iqn.20...www:disk/tpg1> ls
o- tpg1 ..................................................................................................... [no-gen-acls, no-auth]
o- acls ................................................................................................................ [ACLs: 1]
| o- iqn.2019-04.com.test.www:xx ................................................................................ [Mapped LUNs: 2]
| o- mapped_lun0 ...................................................................................... [lun0 block/block1 (rw)]
| o- mapped_lun1 ...................................................................................... [lun1 block/block2 (rw)]
o- luns ................................................................................................................ [LUNs: 2]
| o- lun0 ............................................................................................. [block/block1 (/dev/sdb1)]
| o- lun1 ............................................................................................. [block/block2 (/dev/sdb2)]
o- portals .......................................................................................................... [Portals: 1]
o- 192.168.1.118:3260 ..................................................................................................... [OK]
/iscsi/iqn.20...www:disk/tpg1>
/iscsi/iqn.20...www:disk/tpg1> exit (退出target子系统)
Global pref auto_save_on_exit=true
Last 10 configs saved in /etc/target/backup.
Configuration saved to /etc/target/saveconfig.json (刚才做到配置的保持位置,修改此配置文件的相关值，重启target服务后，既可修改target的配置)
[root@localhost ~]# iSCSI initiator(客户端)配置：
1.yum install iscsi* -y
iscsiadm是用于管理，查询，插入，更新或删除iSCSI数据库配置文件的命令行工具，用户需要先使用这个工具
扫描发现远程iSCSI服务端，然后查看找到的服务器上有哪些可用的共享存储资源。
2. 发现操作
[root@rhel002 ~]# iscsiadm -m discovery -t st -p 192.168.1.118
192.168.1.118:3260,1 iqn.2019-04.com.test.www:xx #服务端iscsi ACLS名称
[root@rhel002 ~]#
# -m discovery: 扫描并发现可用的存储资源
# -t st参数为执行扫描操作的类型
# -p xxx iSCSI服务端的IP地址
3.编辑/etc/iscsi/initiatorname.iscsi 文件，修改InitiatorName值
InitiatorName=iqn.2019-04.com.test.www:xx #注意此处应该设置的值为ISCSI服务端的 acls值
4.重启服务
[root@rhel002 ~]# systemctl restart iscsid
[root@rhel002 ~]# systemctl enable iscsid
5.登录服务端:
[root@rhel002 ~]# iscsiadm -m node -T iqn.2019-04.com.test.www:disk -p 192.168.1.118 -l
Logging in to [iface: default, target: iqn.2019-04.com.test.www:disk, portal: 192.168.1.118,3260] (multiple)
Login to [iface: default, target: iqn.2019-04.com.test.www:disk, portal: 192.168.1.118,3260] successful.
[root@rhel002 ~]#
# -m node :将客户端所在主机作为一台节点服务器
# -T xxxx :指定要使用的存储资源
# -l:进行登录验证
6.
[root@rhel002 ~]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 20G 0 disk
├─sda1 8:1 0 500M 0 part /boot
└─sda2 8:2 0 19.5G 0 part
├─rhel-swap 253:0 0 2G 0 lvm [SWAP]
└─rhel-root 253:1 0 17.5G 0 lvm /
sdb 8:16 0 3.7G 0 disk
sdc 8:32 0 3.7G 0 disk
sr0 11:0 1 3.6G 0 rom /mnt/cdrom
[root@rhel002 ~]#
这里的sdb,sdc 就是服务端的分区,对应服务端的luno,lun1
sdb,sdc可以当做本地的分区来使用,再对sdb,sdc进行分区格式化后，需要永久挂载时需注意,
/etc/fstab中相应的配置行的挂载参数需写成defaults,_netdev,范例如下；
/dev/sdb1 /mnt/netdisk xfs defaults,_netdev 0 0
如缺少_netdev值，则重启时，系统将无法成功启动
可以使用 lsscsi命令查看SCSI控制器设备的信息:
[root@rhel002 ~]# lsscsi
[2:0:0:0] disk VMware, VMware Virtual S 1.0 /dev/sda
[4:0:0:0] cd/dvd NECVMWar VMware SATA CD01 1.00 /dev/sr0
[34:0:0:0] disk LIO-ORG block1 4.0 /dev/sdb
[34:0:0:1] disk LIO-ORG block2 4.0 /dev/sdc
[root@rhel002 ~]#
iscsiadm -m session [-P #] 命令可以查看与服务端的连接属性,#取值范围为0-3,表示显示信息的详细程度，不带-P 选项的话默认为-P 0
[root@rhel002 ~]# iscsiadm -m session
tcp: [2] 192.168.1.118:3260,1 iqn.2019-04.com.test.www:disk (non-flash)
[root@rhel002 ~]# iscsiadm -m session -P 1
Target: iqn.2019-04.com.test.www:disk (non-flash)
Current Portal: 192.168.1.118:3260,1
Persistent Portal: 192.168.1.118:3260,1
**********
Interface:
**********
Iface Name: default
Iface Transport: tcp
Iface Initiatorname: iqn.2019-04.com.test.www:xx
Iface IPaddress: 192.168.1.117
Iface HWaddress: <empty>
Iface Netdev: <empty>
SID: 2
iSCSI Connection State: LOGGED IN
iSCSI Session State: LOGGED_IN
Internal iscsid Session State: NO CHANGE
[root@rhel002 ~]#
7.如何临时断开与服务端的指定连接 ：(重启客户端后还会连接)
iscsiadm -m node -T iqn.2019-04.com.test.www:disk -p 192.168.1.118 -u
# -u :卸载
[root@rhel002 ~]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 20G 0 disk
├─sda1 8:1 0 500M 0 part /boot
└─sda2 8:2 0 19.5G 0 part
├─rhel-swap 253:0 0 2G 0 lvm [SWAP]
└─rhel-root 253:1 0 17.5G 0 lvm /
sr0 11:0 1 3.6G 0 rom /mnt/cdrom
[root@rhel002 ~]#
8.删除与服务端的指定连接:(彻底与服务端断开连接，重启也不会再连接服务端)
iscsiadm -m node -T iqn.2019-04.com.test.www:disk -p 192.168.1.118 -o delete
(删除连接后如想再连接服务端，需先重新发现一下(iscsiadm -m discovery -t st -p 192.168.1.118),然后再重新登录服务端)
9.如何断开与服务端的所有连接:
iscsiadm -m node -u ALL
10.如何删除与服务端的所有连接:
iscsiadm -m node -o delete来源：https://blog.51cto.com/3037673/2427881