This chapter covers basic information about configuring host groups and host access, host topology, and I/O data path protection.
A host is a system that accesses a storage array and is mapped to the virtual disks through one or more host connections. Hosts have the following attributes:
Host name — A name that uniquely identifies the host.
Host type — The operating system running on the host.
Host connection — A physical connection to the host server. Host connections can be automatically detected by MD Storage Manager and can be identified by an alias assigned by the user.
Host group — A host may be associated with other hosts to share access to the same virtual disks.
Configuring Host Access
Configuring host access allows you to either permit or deny access to a storage array for specific hosts. When you permit host access, that host can then be mapped to a virtual disk on the storage array. On the Summary tab, the Hosts & Mappings area indicates how many hosts are configured to access the array. Click Configured Hosts in this area to see the names of these hosts.
Host access configuration is the first step in setting up your storage array. You must complete this task during initial setup and anytime you connect a new host.
After you configure host access, the host does not yet have the ability to write data to the storage array. You must map hosts to the virtual disks and register virtual disks with the host's operating system before a host can write to the storage array. See
Disk Groups and Virtual Disks for information on these tasks.
To begin configuring host access, click the Configure tab and then click either Configure Host Access (Automatic) or Configure Host Access (Manual). See the appropriate section for manual configuration, depending on whether you are using SAS HBA or iSCSI.
Automatic Configuration
NOTE: The host must be connected (iSCSI or SAS) and the host agent restarted after the connection is made in order to use automatic configuration.
To automatically configure a host for access to the storage array:
Click the Configure tab and then click Configure Host Access
(Automatic).
To see hosts that already have access to the storage array, click View
configured hosts.
Select the hosts you want to give access to the storage array in the
Available hosts window.
To see the ports and the host type for the selected hosts, click View Details
at the right of the list.
Click Add to move specific hosts to the Selected hosts window.
Click OK to configure access for the hosts you selected.
Manual Configuration (using SAS HBA)
NOTE: Host access that is manually configured requires special attention to ensure that the correct SAS host port World Wide IDs are selected for each host. If any incorrect IDs are configured, an inaccurate topology will result. You can use the SAS/5/E HBA BIOS Setup program to identify the World Wide IDs for the SAS host ports.
Configure the host to make it available to the storage array for logical unit number (LUN) mapping by following these steps.
Click the Configure tab and then click Configure Host Access (Manual).
Type a name of your choice in the Enter host name text box.
This can be an informal name, not necessarily a name used to identify the host to the network.
Select the operating system of your host in the Select host type box and
then click Next.
Specify the HBA host ports by choosing known host ports or by manually
defining host ports.
To select a host port that is already recognized by MD Storage Manager, click a host port in the Known HBA host ports list, then click Add.
To manually define a host port, click New, enter the HBA host port and Alias in the Enter New HBA Host Port dialog box, and then click Add.
Click Next.
Indicate whether the host is part of a host group (cluster):
If the host is not part of a host group, select No.
If the host is part of a host group, select Yes:
To create a new host group, enter a name in the Enter new host group name text box.
To add the host to an existing host group, select the host group from the Select existing host group box.
Click Next.
Click Finish to configure the host.
Manual Configuration (using iSCSI)
Configure the host to make it available to the storage array for LUN mapping by following these steps.
Click the Configure tab and then click Configure Host Access (Manual).
Type a name of your choice in the Enter host name text box.
This can be an informal name, not necessarily a name used to identify the host to the network.
Select the operating system of your host in the Select host type drop-down
box and then click Next.
Specify the iSCSI initiators by choosing known initiators or by manually
defining initiators.
To select an initiator that is already recognized by MD Storage Manager, click an initiator in the Known iSCSI Initiators list, and then click Add.
To manually define an initiator, click New, enter the iSCSI initiator name and iSCSI initiator label in the Enter new iSCSI initiator dialog box, and then click Add.
NOTE: The initiator name entered must match the name on a host server that will connect to the storage array.
NOTE: In order for the host to be recognized, it must be connected with an iSCSI session.
Click Next.
Indicate whether the host is part of a host group (cluster):
If the host is not part of a host group, select No.
If the host is part of a host group, select Yes:
To create a new host group, enter a name in the Enter new host group name text box.
To add the host to an existing host group, select the host group from the Select existing host group box.
Click Next.
Click Finish to configure the host.
Removing Host Access
Use the following procedure to remove a host's access to a storage array:
Click the Modify tab, then click Edit topology.
In the host topology list, click the plus sign (+) to the left of the host
group name.
The host group expands to show the hosts in the group.
In the list, click the name of the host whose access you want to remove,
and then click Remove located to the right of the list. Click Yes to remove
access.
Repeat step 3 for each host whose access you want to remove.
When the list contains only those hosts you want to access the storage
array, click Close beneath the list.
Host Groups
A host group is a logical entity of two or more hosts that share access to specific virtual disks on the storage array. You create host groups with MD Storage Manager.
All hosts in a host group must have the same host type (operating system). In addition, all hosts in the host group must have special software, such as clustering software, to manage virtual disk sharing and accessibility.
If a host is part of a cluster, every host in the cluster must be connected to the storage array, and every host in the cluster must be added to the host group.
Use the following procedures to create a host group, to add or remove hosts from a host group, or to delete a host group.
Creating a Host Group
Click the Configure tab and then click Create Host Group.
Type a name for the new host group in the Enter new host group name
text box.
In the Select hosts to add list, click the name of a host you want to add to
the host group, then click Add.
The host moves to the Hosts in group list.
Repeat step 3 until all the hosts you want to add to the host group are
moved into the Hosts in group list.
Click OK.
Adding a Host to a Host Group
Click the Modify tab, then click Edit Host Topology.
A list of hosts and host groups appears.
In the host topology list, click the plus sign (+) to the left of the host
group name.
The host group expands to show the hosts in the group.
Click the host you want to move and click Move.
Select the host group to which you want to move the host.
Click OK.
The host is moved into the host group.
The host retains the virtual disk mappings assigned to it, and inherits the virtual disk mappings assigned to the group. Other hosts in the group do not inherit the mappings of the added host.
Removing a Host From a Host Group
Click the Modify tab, then click Edit Host Topology.
A list of hosts and host groups appears.
In the host topology list, click the plus sign (+) to the left of the host
group name.
The host group expands to show the hosts in the group.
Click the name of the host you want to remove from the group.
Click Remove located to the right of the list.
Click Yes to remove the host.
The host is moved out of the host group. The host retains the virtual disk mappings assigned to it, and loses the virtual disk mappings assigned to the group.
Moving a Host to a Different Host Group
Click the Modify tab, then click Edit Host Topology.
A list of hosts and host groups appears.
In the host topology list, click the plus sign (+) to the left of the host
group name.
The host group expands to show the hosts in the group.
Click the name of the host you want to move to another group and click
Move.
Select the host group to which you want to move the host.
Click OK.
The host is moved to the indicated host group.
The host retains the virtual disk mappings assigned to it, and inherits the virtual disk mappings assigned to the group to which it is moved. The host loses the virtual disk mappings assigned to the group from which it was moved.
Removing a Host Group
This section covers removing an entire host group. To remove a single host from a host group, see Removing a Host From a Host Group.
Click the Modify tab, then click Edit Host Topology.
In the host topology list, click the name of the host group you want to
remove.
Click Remove.
Click Yes.
The host group and its assigned virtual disk mappings are removed.
NOTE: If the host group contains hosts, those hosts are removed as well, including their access to the storage array.
Host Topology
Host topology is the organization of hosts, host groups, and host interfaces configured for a storage array. The Edit Host Topology screen accessed from the Modify tab shows the hierarchy of the host groups, the hosts that are part of each host group, and the host connections of each host.
You can use these tasks to change the host topology:
Move a host or a host connection
Rename a host group, a host, or a host connection
Add a host connection
Replace a host connection
Change a host type
MD Storage Manager automatically detects these changes for any host running the host agent software.
Host Context Agent
The host context agent discovers the host topology. The host context agent starts when the host is started and stops when the host is turned off. The topology discovered by the host context agent can be viewed by clicking Configure Host Access (Automatic) in the Configure tab in the MD Storage Manager.
You must stop and restart the host context agent to see the changes to the host topology if any of the following situations occur:
A new storage array is attached to the host server.
A host is added while turning on power to the RAID controller modules.
Linux
In Linux, you can stop and start the host context agent from the command line. Use the following syntax: SMagent start or SMagent stop.
You will stop and then restart SMagent after performing either of the two following maintenance tasks.
Moving a controller offline or replacing a controller.
Removing host-to-array connections from or attaching host-to-array connections to a Linux host server.
Windows
In Windows, you can stop and start the host context agent from the Services option of the Administrative Tools. To access the host context agent:
From the list of services, select Modular Disk Storage Manager Agent.
I/O Data Path Protection
You can have multiple host-to-array connections for a host. Make sure to select all of the connections to the array when configuring host access to the storage array.
NOTICE: Refer to the Installation Guide for more information on cabling configurations.
NOTE: For maximum redundancy, you must select all host connections to the array when manually defining host topology. For example, a host might have two host connections listed when manually configuring host access. For this host, you would select the two host connections listed in the "Available hosts" section and add them to the "Selected hosts" section using the Add button.
NOTE: For more information on configuring hosts see About Your Host.
If a component such as a RAID controller module or a cable fails, or an error occurs on the data path to the preferred RAID controller module, virtual disk ownership is moved to the alternate nonpreferred RAID controller module for processing. This failure or error is called failover.
Multi-path drivers such as MPIO and MPP are installed on host systems that access the storage array and provide I/O path failover. The multi-path driver (MPIO in Windows and MPP in Linux) is used for failover. Automatic Virtual Disk Transfer (AVT) is used specifically for single-port cluster failover. The AVT feature mode is automatically selected by host type.
NOTE: You should have the multi-path driver installed on the hosts at all times, even in a configuration where there is only one path to the storage system, such as a single port cluster configuration.
During a failover, the virtual disk transfer is logged as a critical event, and an alert notification is sent automatically if you have configured alert destinations for the storage array.
