blog.meyawi.com

Introduction

When properly configured, an AIX server can act as :

• iSCSI initiator : access storage devices using TCP/IP on Ethernet network adapters
• iSCSI target : export local storage to be accessed by other iSCSI initiators using the iSCSI protocol

In our case, iSCSI initiator will be an AIX 7.1 (7100-00-03-1115) and the iSCSI target will be a Storwize V7000 Unified.

Configuring iSCSI on V7000U

Let’s check iSCSI configuration on the Storwize.

Port configuration IP

• iSCSI port IP node 1 (port1) : 192.168.251.121
• iSCSI port IP node 2 (port1) : 192.168.251.122

In this example, I used port1 of both nodes, but consider dedicating port2 instead in order to separate management traffic and iSCSI traffic.

iSCSI configuration on AIX

From AIX node, we’ll check that we can ping both iSCSI ports IP address of the Storwize.

   

Now we could configure the iSCSI software initiator.

We’ll use the file Discovey Policy, which means that information about targets are stored in a file (disc_filename) : /etc/iscsi/targets

The initiator name could be changed if needed :

Now, let’s update /etc/iscsi/targets with V7000U iSCSI target ports information.

Each target is defined by 3 fields minimum as follows : HostNameOrAddress PortNumber iSCSIName

192.168.251.121 3260 iqn.1986-03.com.ibm:2145.v7000u.node1
192.168.251.122 3260 iqn.1986-03.com.ibm:2145.v7000u.node2

V7000U : Host creation + Volume mapping

We have to create a new iSCSI host within the V7000U admin interface :

Our AIX test node is named londres-test and the initiator port adress is : iqn.londres.hostid.7f000001

The initiator is found on iscsi0 (lsattr –El iscsi0).

Once the host created, we have to create a volume and map it to our host :

AIX : Disk Discovery & Multipathing

Now that everything seems to be ok, execute cfgmgr to discover the new mapped disk.

Surprise !! Instead of one new disk, we see 2 new disks. So what happened ?!

In fact, it’s the same disk, but multipathing is disabled so the volume appears to be 2 separate devices, one from each V7000U node :

• hdisk2 from node1
• hdisk3 from node2

The host selects one device to perform I/O to the volume, which corresponds to a particular IP address at a Storwize V7000 node port.

If a connection between the host and this Storwize V7000 port is broken, there is no high availibility and an I/O error is recorded on host.

At the time of writing, it seems that iSCSI multipathing is not supported on AIX hosts with software initiator

http://www-01.ibm.com/support/docview.wss?uid=ssg1S1003908#_ISCSI

I tried on a linux redhat distribution (RHEL5), and according to documentation, multipathing seems to be supported :

AIX : iSCSI Initiator Considerations

• iSCSI host and IBM Storwize V7000 Ethernet ports should be directly connected to the same switch
• iSCSI host and IBM Storwize V7000 node Ethernet ports should be running at the same link speed
• The maximum number of configured Volumes tested using the iSCSI software initiator is 128 per iSCSI target.
• Configure volume groups that are created using iSCSI devices to be in an inactive state after reboot.
• For best performance, tune network options : rfc1323, tcp_sendspace, tcp_recvspace, sb_max, mtu_size.