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improve ha-manager intro

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Dietmar Maurer 2016-03-13 13:21:38 +01:00
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@ -48,7 +48,21 @@ percentage of uptime in a given year.
|99.99999 |3.15 seconds |99.99999 |3.15 seconds
|=========================================================== |===========================================================
There are several ways to increase availability: There are several ways to increase availability. The most elegant
solution is to rewrite your software, so that you can run it on
several host at the same time. The software itself need to have a way
to detect erors and do failover. This is relatively easy if you just
want to serve read-only web pages. But in general this is complex, and
sometimes impossible because you cannot modify the software
yourself. The following solutions works without modifying the
software:
* Use reliable "server" components
NOTE: Computer components with same functionality can have varying
reliability numbers, depending on the component quality. Most verdors
sell components with higher reliability as "server" components -
usually at higher price.
* Eliminate single point of failure (redundant components) * Eliminate single point of failure (redundant components)
@ -56,19 +70,33 @@ There are several ways to increase availability:
- use redundant power supplies on the main boards - use redundant power supplies on the main boards
- use ECC-RAM - use ECC-RAM
- use redundant network hardware - use redundant network hardware
- use distributed, redundant storage - use RAID for local storage
- use distributed, redundant storage for VM data
* Reduce downtime * Reduce downtime
- automatic error detection - rapidly accessible adminstrators (24/7)
- automatic failover - availability of spare parts (other nodes is a {pve} cluster)
- automatic error detection ('ha-manager')
- automatic failover ('ha-manager')
Virtualization environments like {pve} makes it much easier to reach Virtualization environments like {pve} makes it much easier to reach
high availability because they remove the "hardware" dependency. It is high availability because they remove the "hardware" dependency. They
also easy to setup and use redundant storage and network devices. So also support to setup and use redundant storage and network
if one host fail, you can simply start those services on another host devices. So if one host fail, you can simply start those services on
within your cluster. Even better, 'ha-manager' is able to another host within your cluster. Even better, 'ha-manager' can do
automatically detect errors and do automatic failover. that automatically for you. It is able to automatically detect errors
and do automatic failover.
But high availability comes at a price. High quality components are
more expensive, and making them redundant duplicates the costs at
least. Additional spare parts increase costs further. So you should
carefully calculate the benefits, and compare with those additional
costs.
TIP: Increasing availability from 99% to 99.9% is relatively
simply. But increasing availability from 99.9999% to 99.99999% is very
hard and costly.
'ha-manager' handles management of user-defined cluster services. This 'ha-manager' handles management of user-defined cluster services. This
includes handling of user requests which may start, stop, relocate, includes handling of user requests which may start, stop, relocate,