Creating host groups

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You can group a set of hosts based on your business requirements. For example, you can group the hosts that run similar type of workloads. You can also group important hosts together so that the monitoring and recovery operations can be performed for the set of hosts together and quickly. In disaster situations, you can move a host group separately to the backup site.

Guidelines to manage host groups:

In case of symmetric host group, a host must already be added to the KSYS configuration settings and the host must have been paired with a backup host in the backup site.
Each host in a site must be a part of a host group. If a paired host is not added to any host groups, the host is automatically added to the Default_HG host group during the discovery operation.
If you add or remove hosts from a host group, you must run a discovery operation to manage or unmanage all the virtual machines from the recovery management. The modified host group displays the correct list of managed virtual machines only after a discovery operation.
The corresponding hosts in the backup site that are paired with the active site hosts are grouped logically within the same host group. For example, if host1 in the active site is paired with host2 in the backup site and you create a host group hg1 with host1, then host2 is automatically added to the host group hg1.
Each host group is associated with a separate disk group. The disks in the disk group must not be shared among different host groups. The disk groups are named in the following format:
```
VMRDG_{peer_domain_name}_{site_name}_{host_group_ID}
```
However, the disk group name must not exceed the maximum number of characters that is supported for a consistency group at storage level.

To add hosts to the KSYS configuration, complete the following steps in the KSYS LPAR:

To create a host group and to add the existing hosts that you want to include in this host group, run the following command:
```
ksysmgr add host_group hg1 [site=<Site_1>] hosts=Host_11,Host_12,Host_13 [mxn_pairing=<yes>] [workgroup_support=<no>]
```
Note:
- By default, the mxn_pairing attribute is set to no. You must pair the hosts before adding the hosts to the host group. Once you add one counterpart from the host-pair to a host group, the other counterpart of the host-pair will be automatically added to the respective host group in the other site. These hosts forms symmetric host group, which contains one to one paired hosts.
- To create asymmetric host group, which contains one to many paired hosts, set the mxn_pairing attribute to yes. You should not pair the hosts before adding the hosts to the host group. You must specify host and host-group pair of all hosts manually.
- All the hosts in the backup site that are paired with the specified hosts are also added to the host group.
- By default, the workgroup_support attribute is set to yes. A host group is automatically created with the workgroup. To disable the workgroup support for a host group, set the workgroup_support attribute to no when adding the host group.
- All VMs in the backup site will no longer be managed after the host group is created.
- By default, the KSYS subsystem considers VMs of the home site to create a host group. To create a host group and add VMs of the backup site to the host group, use the site option in the ksysmgr command.
Repeat Step 1 for all host groups that you want to create in the KSYS subsystem.

Optional: To verify the host groups that you added, run the following command:

ksysmgr query host_group hgname

An output that is similar to the following example is displayed:

Name:              hg1
Home Site Hosts:   Host_11
                   Host_12
                   Host_13
Backup Site Hosts: Host_21
                   Host_22
                   Host_23
Workgroups:        none
Memory_capacity:   Priority Based Settings
                   low:100
                   medium:100
                   high:100
CPU_capacity:      Priority Based Settings
                   low:100
                   medium:100
                   high:100
skip_power_on:     No
Sriov_override:    No
Vnic_override:     No
Site:              Site1
Vswitchmap:        Not currently set
Vlanmap:           Not currently set
DrVswitchmap:      Not currently set
DrVlanmap:         Not currently set
Type:              symmetric
Custom CG Name:
Backup Site CG Name:

To add or remove hosts from the existing host groups, run the following command:

ksysmgr modify host_group hg_name add | remove
      hosts=host1,host2... | file=filepath

Where, the file parameter is an XML file that contains a list of hosts. An example of the XML file is as follows:

<KSYSMGR><HOST><NAME>host1</NAME></HOST></KSYSMGR>
<KSYSMGR><HOST><NAME>host2</NAME></HOST></KSYSMGR>
<KSYSMGR><HOST><NAME>host3</NAME></HOST></KSYSMGR>

To modify the capacity-related attributes for all the hosts in a host group, run the following command:

ksysmgr modify host_group hg_name options
      [memory_capacity=<(1-100) | minimum | current_desired | none | default> priority=<low | medium | high>]
      [cpu_capacity=<(1-100) | minimum | current_desired | none | default> priority=<low | medium | high>]
      [skip_power_on=<yes|no>]

For more information about flexible capacity policies, see Configuring the flexible capacity policies.