High Level high[-er] availabilty options
IBM HACMP (High Availability Cluster Multiprocessing) has been available since 1991. It was renamed to IBM PowerHA and, more recently PowerHA System Mirror for AIX. While studying up on this recently, I came across some excellent comparisons between PowerHA, Live Partition Mobility and migration of Worload Partitions (WPARs). This is a high-level comparison of how the three might help with managing outages and make for higher availability, even if they aren't all PowerHA.
LPM and HA
First, Live Partition Mobility (LPM). This is the facility which allows you to migrate a running partition with its applications from one physical server to another without disrupting services. The Redbook for IBM PowerVM Live Partition Mobility explains:
.Live Partition Mobility increases global availability, but it is not a high availability solution. It requires that both source and destination systems be operational and that the partition is not in a failed state. In addition, it does not monitor operating system and application state and it is, by default, a user-initiated action.So LPM is good if the outage is planned.
Unplanned outages still require specific actions that are normally executed by cluster solutions such as IBM PowerHA.
"Live" for a reason
The difference between HA and LPM came home to me recently when I was watching a presentation by an IBMer on PowerHA. Shawn Bodily has worked on HACMP/PowerHA for over ten years. He was on the team that wrote the excellent PowerHA for AIX Cookbookand he presented webinars (see below) over three days in July 2009 on PowerHA (as it was then called). In the second of those days, Shawn answers a question about LPM as an alternative to PowerHA. Here is my transcript of the relevant section:
"When we talk about clustering we talk about reducing planned outages and unplanned outages. Most people associate it [HACMP] with unplanned outages but by far, most downtime today is still planned maintenance and Live Partition Mobility is great for planned maintenance if it's hardware related. If I'm upgrading a server and people can do firmware updates dynamically [i.e. concurrently] and some people choose not to. If I'm doing something like that, Live Partition Mobility is great. Even most of the maintenance is software maintenance. If you have to upgrade your application, update AIX, Live Partition Mobility does nothing for you. Here's why: the fact you're running the exact same rootvg and application on another frame."WPARs for AIX update
- VIOS and
- Lots of other acronyms