iSCSI software initiator considerations

Consider the following when dealing with iSCSI software initiators.

• Target discovery
  The iSCSI software initiator supports the following 4 forms of target discovery:

  file

  A text file is used to configure each target.

  odm

  ODM objects are used to configure each target. When using an iSCSI disk as a boot disk or as part of the rootvg boot, the odm discovery method must be used.

  isns

  Each target is registered in one or more Internet Storage Name Service (iSNS) servers.

  slp

  Each target is registered in one or more Service Location Protocol (SLP) service agents or directory agents.

• iSCSI Authentication

  The iSCSI software initiator uses the local iSCSI qualified name as the Challenge Handshake Authentication Protocol (CHAP) name if the CHAP name is not specified. The targets file or the ODM configuration might specify an alternate CHAP name. For more information about specifying the CHAP name, see the reference information for the targets file or the mkiscsi command.

  Only CHAP (MD5) can be used to configure Initiator authentication. Target authentication is not implemented.

• iSCSI Software Initiator MPIO

  The AIX iSCSI Software Initiator supports Multiple Path I/O (MPIO). If you are using either the file or the ODM discovery policy, add entries to contact multiple ports of a storage device, by using multiple network interfaces in AIX. The iSCSI driver recognizes multiple paths to the same device and configures them in an MPIO configuration. This is similar to the MPIO configuration for other storage device protocols.

  If you are using third party iSCSI disk ODM definitions, ensure that the latest available version of those definitions is installed in order to use multiple paths to iSCSI disks.

• Number of configured LUNs

  The maximum number of configured LUNs tested using the iSCSI software initiator is 128 per iSCSI target. The software initiator uses a single TCP connection for each iSCSI target (one connection per iSCSI session). This TCP connection is shared among all LUNs that are configured for a target. The software initiator's TCP socket send and receive space are both set to the system socket buffer maximum. The maximum is set by the sb_max network option. The default is 1 MB.

• Volumes Groups

  To avoid configuration problems and error log entries when you create volume groups using iSCSI devices, follow these guidelines:

  • Configure volume groups that are created using iSCSI devices to be in an inactive state after reboot. After the iSCSI devices are configured, manually activate the iSCSI-backed volume groups. Then, mount any associated file systems.

    Volume groups are activated during a different boot phase than the iSCSI software driver. For this reason, it is not possible to activate iSCSI volume groups during the boot process.

  • Do not span volume groups across non-iSCSI devices.
• I/O Failures

  If connectivity to iSCSI target devices is lost, I/O failures occur. To prevent I/O failures and file system corruption, stop all I/O activity and unmount iSCSI backed file systems before doing anything that will cause long term loss of connectivity to active iSCSI targets.

  If a loss of connectivity to iSCSI targets occurs while applications are attempting I/O activities with iSCSI devices, I/O errors will eventually occur. It might not be possible to unmount iSCSI backed file systems because the underlying iSCSI device stays busy.

  File system maintenance must be performed if I/O failures occur due to loss of connectivity to active iSCSI targets. To do file system maintenance, run the fsck command.

• Do not use the AIX® iSCSI software initiator or the AIX iSCSI software target with the loopback interface (lo0). The processing of the loopback interface interrupt differs from the processing of the physical or virtual Ethernet adapter network interface interrupt. The AIX operating system might stop operations if the loopback interface is used with the iSCSI software drivers.