Install and Configure Multipath on Centos

Server 1 : test1


213.x.x.x - eth0
10.50.68.15 - eth1

Server 2 : test2
31.x.x.x - eth0
10.50.68.16 - eth1

Step 1:

Create an LVM on test1 and make this LVM as target.

Step 2:

On test2, Login to target you created on test1 using both ip's.

iscsiadm -m discovery -t sendtargets -p 213.x.x.x
iscsiadm -m node -T iqn.2008-09.com.example:first -p 213.x.x.x -l
 iscsiadm -m discovery -t sendtargets -p 10.50.68.15
 iscsiadm -m node -T iqn.2008-09.com.example:first -p 10.50.68.15 -l

[root@test ~]# lsblk
NAME  MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
xvda1 202:1    0  15G  0 disk /
xvda2 202:2    0   2G  0 disk [SWAP]
sda     8:0    0   4G  0 disk
sdb     8:16   0   4G  0 disk

The same target will show like two disks on test2.

On test1:

[root@test ~]# tgt-admin --show
Target 1: iqn.2008-09.com.example:first
    System information:
        Driver: iscsi
        State: ready
    I_T nexus information:
        I_T nexus: 5
            Initiator: iqn.1994-05.com.redhat:test2
            Connection: 0
                IP Address: 31.x.x.x
        I_T nexus: 6
            Initiator: iqn.1994-05.com.redhat:test2
            Connection: 0
                IP Address: 10.50.68.16
    LUN information:
        LUN: 0
            Type: controller
            SCSI ID: IET     00010000
            SCSI SN: beaf10
            Size: 0 MB, Block size: 1
            Online: Yes
            Removable media: No
            Prevent removal: No
            Readonly: No
            Backing store type: null
            Backing store path: None
            Backing store flags:
        LUN: 1
            Type: disk
            SCSI ID: IET     00010001
            SCSI SN: beaf11
            Size: 4295 MB, Block size: 512
            Online: Yes
            Removable media: No
            Prevent removal: No
            Readonly: No
            Backing store type: rdwr
            Backing store path: /dev/vgsrv/storage
            Backing store flags:
    Account information:
    ACL information:
        31.x.x.x
        10.50.68.16

On test2:
[root@test ~]# iscsiadm -m session -P3
iSCSI Transport Class version 2.0-870
version 6.2.0-873.13.el6
Target: iqn.2008-09.com.example:first (non-flash)
    Current Portal: 213.x.x.x:3260,1
    Persistent Portal: 213.x.x.x:3260,1
        **********
        Interface:
        **********
        Iface Name: default
        Iface Transport: tcp
        Iface Initiatorname: iqn.1994-05.com.redhat:test2
        Iface IPaddress: 31.x.x.x
        Iface HWaddress: <empty>
        Iface Netdev: <empty>
        SID: 6
        iSCSI Connection State: LOGGED IN
        iSCSI Session State: LOGGED_IN
        Internal iscsid Session State: NO CHANGE
        *********
        Timeouts:
        *********
        Recovery Timeout: 2
        Target Reset Timeout: 2
        LUN Reset Timeout: 2
        Abort Timeout: 2
        *****
        CHAP:
        *****
        username: <empty>
        password: ********
        username_in: <empty>
        password_in: ********
        ************************
        Negotiated iSCSI params:
        ************************
        HeaderDigest: None
        DataDigest: None
        MaxRecvDataSegmentLength: 262144
        MaxXmitDataSegmentLength: 8192
        FirstBurstLength: 65536
        MaxBurstLength: 262144
        ImmediateData: Yes
        InitialR2T: Yes
        MaxOutstandingR2T: 1
        ************************
        Attached SCSI devices:
        ************************
        Host Number: 5    State: running
        scsi5 Channel 00 Id 0 Lun: 0
        scsi5 Channel 00 Id 0 Lun: 1
            Attached scsi disk sdb        State: running
    Current Portal: 10.50.68.15:3260,1
    Persistent Portal: 10.50.68.15:3260,1
        **********
        Interface:
        **********
        Iface Name: default
        Iface Transport: tcp
        Iface Initiatorname: iqn.1994-05.com.redhat:test2
        Iface IPaddress: 10.50.68.16
        Iface HWaddress: <empty>
        Iface Netdev: <empty>
        SID: 7
        iSCSI Connection State: LOGGED IN
        iSCSI Session State: LOGGED_IN
        Internal iscsid Session State: NO CHANGE
        *********
        Timeouts:
        *********
        Recovery Timeout: 2
        Target Reset Timeout: 2
        LUN Reset Timeout: 2
        Abort Timeout: 2
        *****
        CHAP:
        *****
        username: <empty>
        password: ********
        username_in: <empty>
        password_in: ********
        ************************
        Negotiated iSCSI params:
        ************************
        HeaderDigest: None
        DataDigest: None
        MaxRecvDataSegmentLength: 262144
        MaxXmitDataSegmentLength: 8192
        FirstBurstLength: 65536
        MaxBurstLength: 262144
        ImmediateData: Yes
        InitialR2T: Yes
        MaxOutstandingR2T: 1
        ************************
        Attached SCSI devices:
        ************************
        Host Number: 6    State: running
        scsi6 Channel 00 Id 0 Lun: 0
        scsi6 Channel 00 Id 0 Lun: 1
            Attached scsi disk sda        State: running



Step 4:

Install & configure multipath on test2,

yum  install  device-mapper-multipath
mpathconf --user_friendly_names n
service multipathd start

Then,
[root@test ~]# ls -la /dev/mapper/1IET_00010001
lrwxrwxrwx 1 root root 7 Apr  2 00:01 /dev/mapper/1IET_00010001 -> ../dm-0
[root@test ~]# lsblk
NAME                   MAJ:MIN RM SIZE RO TYPE  MOUNTPOINT
xvda1                  202:1    0  15G  0 disk  /
xvda2                  202:2    0   2G  0 disk  [SWAP]
sda                      8:0    0   4G  0 disk 
└─1IET_00010001 (dm-0) 253:0    0   4G  0 mpath
sdb                      8:16   0   4G  0 disk 
└─1IET_00010001 (dm-0) 253:0    0   4G  0 mpath

Testing Multipath,

[root@test ~]# multipath -ll
1IET_00010001 dm-0 IET,VIRTUAL-DISK
size=4.0G features='0' hwhandler='0' wp=rw
|-+- policy='round-robin 0' prio=1 status=active
| `- 6:0:0:1 sda   8:0   active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
  `- 5:0:0:1 sdb   8:16  active ready running

[root@test ~]# ifdown eth1

[root@test ~]# multipath -ll
1IET_00010001 dm-0 IET,VIRTUAL-DISK
size=4.0G features='0' hwhandler='0' wp=rw
|-+- policy='round-robin 0' prio=0 status=active
| `- 6:0:0:1 sda   8:0   active faulty running
`-+- policy='round-robin 0' prio=1 status=enabled
  `- 5:0:0:1 sdb   8:16  active ready  running

[root@test ~]# ifup eth1

[root@test ~]# multipath -ll
1IET_00010001 dm-0 IET,VIRTUAL-DISK
size=4.0G features='0' hwhandler='0' wp=rw
|-+- policy='round-robin 0' prio=1 status=active
| `- 6:0:0:1 sda   8:0   active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
  `- 5:0:0:1 sdb   8:16  active ready running

Now If one path fails [e.g sda] but still the storage will accessible by another path[e.g sdb].

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