iSER support

Be aware of the following general iSER support considerations.

The general iSER parameters are applicable regardless of the operating system.

  • The system supports:
    • The standard iSER target port for iSER logins over RoCE ports is 3260.

      The standard iSER target port for iSER logins over iWARP ports is 860.

      The port type is displayed in the rdma_type field in the output of either the svcinfo lsportip or sainfo lsservicestatus commands.

    • A maximum of 512 hosts per I/O group for all supported node types.
    • Up to 256 sessions per system iSER target from different iSER hosts. A maximum of 512 sessions per I/O group from iSER hosts with up to four sessions from one iSER host to each system iSER target.
    • I/O from Fibre Channel and iSER initiators in different hosts to the same volumes.
      Note: The system does not support I/O from Fibre Channel and iSCSI initiators in the same hosts to the same volumes.
    • Multiple sessions from iSER hosts, with a maximum of four sessions from one iSER host to each system iSER target.
    • One-way CHAP authentication, where you can specify an authentication user name with a maximum of 31 ASCII characters, or you can use the initiator's IQN as the user name.
    • Hosts that are compliant with SPC-3 SCSI Spec Persistent Reserve implementation.
    • I/O from different initiators in the same host to the same I/O group.
    • I/O from different initiators in different hosts to the same volumes.
    • Both the iSNS Protocol (allowing iSER initiators to locate appropriate storage resources that use the internet Storage Name Service) and CHAP-based authentication (associating iSER authentication information with a host object).
    • iSER host attachment, with each node that acts as an iSER target.
  • iSER uses either iSCSI qualified name (IQN) (223 bytes) or extended unique identifier (EUI) (64-bit) names.
    Note: Ensure that the IP takeover facility in an I/O group is enabled. To ensure that the IP takeover facility in the I/O group is enabled, run the svcinfo lsportip command. In the output, verify that partner nodes in the I/O group have the same number and type (speed, rdma_type) of Ethernet ports. Also, verify that the same numbered ports on both nodes of every I/O group have IPs configured for host attachment. For more information about how to set IP, see the svctask cfgportip command.

    Then, if the node that is acting as the iSER target fails, the partner node takes over the IP addresses of the failed node, thus continuing operations. During takeover, the iSER initiator is logged out from the failed node. A new session or login is reestablished with the partner (working) node that uses the IP address of the failed node. For successful iSER logins from a host to a partner node after a failover, the port type (RoCE or iWARP) and the number of ports must be the same on the partner nodes. The output of the lsportip command can confirm this. Both the nodes in an I/O group must have either RoCE or iWARP adapters on the same slots. A host session to a RoCE port cannot failover to an iWARP port, and a host session to an iWARP port cannot failover to a RoCE port.

  • Each iSER target can support both IPv4 and IPv6 concurrently. However, a single host establishes only an IPv4 login or a IPv6 log in to an iSER target. If an IPv6 iSER login is initiated by the host while an IPv4 iSER login exists, the IPv6 login is rejected. If an IPv4 iSER login is initiated by the host while an IPv6 iSER login exists, the IPv4 login is rejected.
  • Host operating systems such as Linux® that have many Ethernet interfaces are subject to an Address Resolution Protocol (ARP) Flux problem. This problem might occur when a host replies to ARP requests for interfaces on the same or different subnet from any interface on that same or different subnet. In most cases, this behavior is not a problem. However, in specific cases, ARP Flux generates unexpected behavior of applications due to an incorrect mapping between IPv4 addresses and MAC addresses.
    To avoid ARP Flux on Linux, use the following setting on the host:
    echo 1 > /proc/sys/net/ipv4/conf/all/arp_filter OR

    To make this behavior persistent, add a net.ipv4.conf.all.arp_filter=1 entry in /etc/sysctl.conf.

    If you use other operating systems such as VMware ESX, check your settings to avoid ARP Flux on those hosts as well.

  • Volumes are mapped to a host that uses the same host-mapping mechanism as Fibre Channel attachment. A volume can be mapped to a Fibre Channel host or an iSER host. Mapping a volume through both iSER and Fibre Channel to the same host is not supported.
  • All IP addresses (service and configuration) associated with a clustered-system Ethernet port must be on the same subnet. However, IP addresses associated with a node Ethernet port that is used for iSER traffic can be configured to belong to different subnets.
  • You must create a host object with a different name for use with each iSER client if either of the following situations is true:
    • A host has multiple iSER clients (multiple IQNs).
    • A clustered-system host server that has multiple iSER names and different authentication secrets is to be used with a different client.
    You must use the appropriate IQNs and corresponding secrets in each of the corresponding host objects, and then use all the host objects to map the volume.
  • The system assigns a host port group ID to a target port. The host port group ID plays a significant role in iSER discovery and login.
    • A host port group ID is an automatic grouping of ports that is designated by an integer. Host port group IDs are unique across I/O groups.
    • When you use the cfgportip -host/host_6 yes command, only the host port group ID is assigned.
    • Each host port group ID contains a maximum of four ports.
    • All ports within a host port group ID have identical speeds and port type, either iWARP or RoCE. Ports with identical speeds but different port types have different host port group IDs.
    • Identical host port group IDs are assigned to the failover port.
  • Discovery from an iSER host to a system target IP address with a specific host port group ID returns all the iSER ports that belong to that host port group ID.

    Discovery to a target IP address with a host port group ID other than the target IP address to which the host is already logged in to results in no IPs returned as a part of discovery. If a host, for example, is logged in to a set of target IPs on ports that belong to host port group ID 1, discovery to a target IP address that belongs to host port group ID 2 returns no IP addresses.

  • An IQN is allowed to establish sessions with a system node that belongs to a single host port group ID. Hence, it is important to select which host port group ID to establish sessions with, based on matching host and target port speed and network topology.
  • There is a common host object definition for iSER and iSCSI hosts with the same IQN. A single host can establish either iSCSI sessions or iSER sessions to the same iSER target. If an iSER session is initiated by the host while an iSCSI session exists from the same host, the iSER session is rejected. Likewise, if an iSCSI session is initiated by the host while an iSER session exists from the same host, the iSCSI session is rejected.