Operating Systems

Other: All the LPARs that are to be mobile must be on the same network with resource monitoring and control (RMC) subsystem connections established to the HMC. If active memory sharing (AMS) is being used, then the destination must have a paging device available for the mobile LPAR. If the LPAR is using active memory expansion (AME), then AME must be supported on the destination server as well.

Not only must the storage be virtualized, but it also has to be zoned correctly. For vSCSI, both the source and target HBAs must be zoned. For NPIV, each virtual Fibre Channel adapter has two worldwide port names (WWPNs)—these both have to be zoned for LPM to work. Additionally, whole LUNs need to be passed across (if vSCSI); logical volume manager (LVM-) based disks can’t be used and all hdisks must be external and set to reserve_policy=no_reserve. Details on this are provided in the LPM Redbook.

Migrating Between Different Server Types

Instruction sets between POWER6, POWER6+ and POWER7/7+ differ, which causes some issues with migration back to the older technology if care isn’t taken. Migration from POWER6 to POWER6+, POWER7 or POWER7+ is very straightforward. The LPAR will run in POWER6 compatibility mode once it’s on the new server and will remain in that mode unless it’s changed and rebooted. If it’s in POWER6 compatibility mode, then it’s easy to migrate it back to the POWER6 if necessary. Migrating from POWER7 to POWER7+ and back involves no compatibility modes, as they use the same instruction set; however, it’s important to check that the LPAR being migrated is set to an entitlement of at least 0.1 (not 0.05) when migrating from POWER7+ to POWER7, as 0.1 is the minimum supported on POWER7.

Migration Phases

There are slightly different rules for inactive vs. active migrations and they both go through a slightly different set of phases. For an active migration, the phases consist of validating the configuration, creating the new LPAR, creating the new virtual resources, migrating the state of the LPAR in memory, removing the old LPAR configuration and freeing up the old resources. For an inactive migration, the phases consist of validating the configuration, creating the new LPAR, creating the new virtual resources, removing the old LPAR configuration and freeing up the old resources.

In the validation phase, the hypervisor and HMC perform checks to ensure the migration will go through with minimal risk. Checks are performed on capabilities and compatibility (hypervisor, VIOS and MSPs), RMC connectivity, partition readiness, target system resource availability, virtual adapter mapping, operating system and application readiness as well as the uniqueness of the LPAR name and whether the number of current active migrations is less than the number of supported active migrations.

If validation passes, then the migration phase begins. The HMC creates an LPAR on the target and configures the MSPs that connect to the hypervisor to set up a private channel to transfer partition state data. The HMC creates the target virtual devices and adapters and then the MSP on the source starts sending partition state data to the target. Once almost all pages are moved, the MSP on the source has the hypervisor suspend the mobile partition while the last modified memory pages and state data are moved. The partition is resumed on the destination and any uncompleted I/O is recovered, and cleanup begins on the source.

Remote migration: Remote migration is the ability to move LPARs between two servers on different HMCs. To do this, a minimum of v7.3.4 of the HMC software is required along with network access between the two HMCs. SSH key authentication needs to be set up to the remote HMC and all involved LPARs (VIOS and mobile LPARs).

Summary

LPM is a valuable tool for any data center that regularly does migrations to new technology or that needs to do firmware and other updates without taking outages. As long as you’ve done proper planning, LPM can save significant time and allow for shorter maintenance windows.

References

For more information on LPM, check out the following resources:

• LPM Redbook: www.redbooks.ibm.com/redbooks/pdfs/sg247460.pdf
• LPM Prerequisites: http://pic.dhe.ibm.com/infocenter/powersys/v3r1m5/index.jsp?topic=/p7hc3/p7hc3firmwaresupportmatrix.htm
• LPM Demo: www.circle4.com/movies/lpm/index.html
• AIX Virtual User Group (lots of topics including LPM): www.tinyurl.com/ibmaixvug.

 

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