It’s pretty new feature on IBM i, for AIX its availably since 2007. In VMware world its called VMotion. In my opinion it is still not very popular. Software vendors must still adopt their software for seamless migrations. But IBM gave us a technology which works very well.
It brings for a system administrator following benefits
- sysadmin can move a LPAR to a different physical box without any downtime for an application and users
What do you need to run it?
- HMC 7.7.5
- PowerVM Enterprise edition
- Use an external storage (boot from SAN)
- LPAR must be fully virtualized , no physical adapters attached, neither use HEA
- Source and target LPAR must talk to the same storage array (or SVC)
- System firmware must support it (check IBM website)
How does it really works?
I’m not a developer, thus I can only repeat what I have read on technical websites.
LPM function copies content of memory in RAM to a target machine (no idea how IBM achieved this with Single Level Storage). When RAM is copied over, all IO transaction are suspended for a short period of time, and they are redirected to the 2nd NPIV adapter (when NPIV is used). The first adapter become unused, and all IO transactions are handled by the second adapter only which is already connected to the target machine.
Best practices
- Do LPM when a system is low utilized. If you do it in peak hours- the migration may take ages.
- Use high speed adapters for migration
- Use jumbo frames if possible
- Double check that 2nd NPIV adapter is properly zoned, if you use vSCSI the storage must be zoned to both source and target Virtual I/O Servers
- Double check that you have software keys for a target machine
- Close the console connection
I’m attaching a screen shots from a migration which I’ve done about 2 years ago.
IBMi.org - Bart's blog 
Great post Bart.
It also important to close the console connection, the migration will fail.
Tip: make use of the exit program for LPM, in this way eg. keys can be applied at migration time.