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Power Enterprise Pools - Multiple HMC Support

By STEPHANIE JENSEN posted Wed June 24, 2020 10:26 PM


HMC V8R8.5.0, which became available at the end of May 2016, introduces multiple HMC support for Power enterprise pools.  To enable multiple HMC support, you are required to update all of the HMCs you want to manage your Power enterprise pool to V8R8.5.0, but you do not need to update any of the servers in your pool.

With multiple HMC support for Power enterprise pools, now you can have as many HMCs as you want managing your pool.  In addition:

  • A pool can have an unlimited number of partitions across the servers in the pool.
  • Additional eligible servers anywhere in your enterprise can be added to an existing pool.
  • If your enterprise has multiple sites you can have one pool and manage mobile resources across your entire enterprise (contractually limited to the same country).  Note that you still must have separate pools for mid-range servers (Power 770+ / E870 systems) and high-end servers (Power 780+ / 795 / E880 systems).          

The Master HMC and Managing HMCs

A Power enterprise pool is required to have a single master HMC.  All pool requests with the exception of most view requests are routed through the master HMC.  The concept of a backup master HMC has gone away.  Now every HMC managing a pool is a backup master HMC.

To add a managing HMC to a pool you specify the HMC’s host name or IP address and a user ID and password.  The user ID and password are not persisted on the HMC and are only used once to establish an ssh session to the HMC being added.  The ssh session is only used to establish a Resource Monitoring and Control (RMC) session between the HMCs.  All pool communication between HMCs is done using the RMC session.  The RMC session is established each time an HMC needs to communicate with another HMC and is terminated after the communication finishes.  Therefore if you have firewalls between your HMCs, ongoing user firewall authentication needs to occur.

You can add HMCs to a pool when you create it.  You can add additional HMCs to an existing pool at any time.  Only HMCs added to a pool can view or manage the pool.  You must add at least one HMC managing each server in your pool.  However, we recommend that you add all of the HMCs that are managing the servers in your pool so that there are redundant paths to each server.  While the master HMC and managing HMCs have special roles for managing a pool, they do provide all other HMC functions.

All managing HMCs must have an active network connection to the master HMC.  The HMCs can communicate on either a public or a private network.  It is recommended that static IP addresses are used for this communication.  The HMCs communicate using the standard RMC port of 657.  The master HMC communicates with all managing HMCs and all managing HMCs communicate with the master HMC.  Managing HMCs do not communicate with each other, except when you are setting a managing HMC as the new master HMC when the current master HMC is down.

To troubleshoot the RMC connection between the master HMC and an HMC managing a pool, run the following diagrmc command on both of the HMCs: diagrmc --mcip  <HMC-IP-address> where HMC-IP-address is the IP address used for pool communication by the other HMC (not the HMC running the command).  For more information about the diagrmc command, see the command's man page.

New GUI for Managing HMCs

On the HMC GUI there are a couple of different ways you can look at the HMCs managing your pool.  You can see a list of the HMCs in your pool and which servers those HMCs are managing.

Or, you can see a list of the servers in your pool and which HMCs are managing those servers.

The first GUI page shown above is the page you now use to set a new master HMC for your pool.  These pages are also used to add HMCs to your pool, remove HMCs from your pool, or reauthenticate HMCs managing your pool.  These pages also show the status of the RMC connection between the master HMC and each managing HMC.

Add and Remove Requests Can Now Be Initiated On Any Managing HMC

Prior to HMC V8R8.5.0, all Power enterprise pool change requests had to be initiated on the master HMC.  With HMC V8R8.5.0, some change requests can now be initiated on any managing HMC.  The following pool requests can be initiated on any managing HMC:

Add processors or memory to a server
Remove processors or memory from a server
View pool information
Synchronize pool information
Set a new master HMC

The following pool requests must still be initiated on the master HMC:

Create pool
Update pool
Recover pool
Remove HMC
Reauthenticate HMC

Setting a New Master HMC For a Pool

The HMC used to create a Power enterprise pool is set as the master HMC for the pool.  You can set a new master HMC at any time.  It is best to set a new master HMC while the current master HMC is running.  If the current master HMC is running, you can initiate the set master operation on any managing HMC.  There are times when you may need to set a new master HMC when the current master HMC is down or not reachable.  To set a new master HMC then, you must initiate the set master operation on the managing HMC that you want to be the new master. 

In HMC V8R8.5.0, only a managing HMC for the pool can be set as the master HMC.  In addition, the master HMC or managing HMCs do not have to manage any servers in the pool. 

Upgrading an Existing Pool to HMC V8R8.5.0

If you have an existing Power enterprise pool it is easy to upgrade your HMCs to V8R8.5.0 and get multiple HMC support for your pool.  You don't even have to upgrade the firmware on any of your servers.  Both HMCs managing your existing pool must be upgraded to V8R8.5.0, but it does not matter if the master HMC or the backup master HMC is upgraded first.  Once one HMC is upgraded to V8R8.5.0, all servers the other HMC is also managing will transition to Version Mismatch state on the other HMC until that HMC is also upgraded.  Once that HMC is upgraded to V8R8.5.0, Version Mismatch state will automatically go away.  If the existing pool has a backup master HMC configured, it will automatically be added as a managing HMC when the master HMC is upgraded. No user actions are required for the pool after upgrading both HMCs to V8R8.5.0 (assuming both HMCs are still managing the pool servers when they are upgraded) and you can start performing operations on your pool again.  If you have additional HMCs you want to manage your pool, you can add them now!

Combining Multiple Existing Pools into One

You may have multiple existing Power enterprise pools that you want to combine into one now that multiple HMC support is available.  To do this you need to decide which pool you want to keep.  The other pool(s) will be deleted.  You must obtain new configuration XML files for all affected pools from IBM.  To start the process, you must fill out the Power Enterprise Pools Change Request form available on the Power Enterprise Pools website and email it to the Power CoD office.  Instructions are on the form.

When you have the new configuration XML files from IBM, follow these steps.

  1. Free all of the mobile resources on all of the servers in a pool to be deleted.  If you have inactive resources on your servers, you may be able to use Elastic CoD or Trial CoD to activate the inactive resources so that you can free and remove the mobile resources without any disruption to your running partitions. 
  2. Remove all of the mobile resources from the servers in the pool.
  3. Update the pool with a new configuration XML file from IBM.  This update will remove all of the servers from the pool then delete the pool. 
  4. Repeat steps 1 - 3 for each pool being deleted.
  5. Once the servers have been removed from each pool being deleted, connect each server to one of the managing HMCs for the pool you are keeping, or add the HMCs managing each server to the pool you are keeping. 
  6. Update the pool you are keeping with a new configuration XML file from IBM.  This update will add the servers to the pool you are keeping.
  7. Now you can add mobile resources to the servers again. 

You can delete servers from a pool one at a time (any server still assigned mobile resources will not be deleted until all mobile resources have been returned to the pool), and add them to a pool one at a time.  You just need to run multiple pool update operations using the same configuration XML file until all of the servers are removed from their old pool and added to their new pool.

Note that mid-range and high-end pools cannot be combined.

More Information

See the Power Enterprise Pools blog.

Knowledge Center documentation is here.

Last updated: October 1, 2016