iSCSI support

Be aware of the following general iSCSI support considerations.

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

The system supports:
- The standard iSCSI port (3260)
- A maximum of 256 hosts
- A maximum of 256 hosts per I/O group for all supported node types.
- Up to 1024 sessions per system iSCSI target from different iSCSI hosts. A maximum of 2048 sessions per I/O group from iSCSI hosts with up to four sessions from one iSCSI host to each system iSCSI target.
- I/O from Fibre Channel and iSCSI 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 iSCSI hosts, with a maximum of four sessions from one iSCSI host to each system iSCSI 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.
- BI-CHAP authentication with initiators that accept a blank user name field.
- 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 iSCSI initiators to locate appropriate storage resources that use the Internet Storage Name Service) and CHAP-based authentication (associating iSCSI authentication information with a host object).
- iSCSI host attachment, with each node that acts as an iSCSI target.
iSCSI 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. Then, if the node that is acting as the iSCSI target fails, the partner node takes over the IP addresses of the failed node, thus continuing operations. During takeover, the iSCSI 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.
Each iSCSI target can support both IPv4 and IPv6 concurrently.
Host operating systems such as Oracle 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 iSCSI host. Mapping a volume through both iSCSI 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 iSCSI traffic can be configured to belong to different subnets.
The system assigns a host port group ID to a target port. The host port group ID plays a significant role in iSCSI 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.
- Identical host port group IDs are assigned to the failover port.
Discovery from an iSCSI host to a system target IP address with a specific host port group ID returns all the iSCSI ports belonging to that host port group ID.
Discovery to a target IP address with a host port group ID other than that of the target IP address to which the host is already logged in to, results in no IPs returned as a part of discovery. For example, if a host 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.