[CentOS] KVM HA

[Chris Adams]

Once upon a time, John R Pierce <pierce at hogranch.com> said:
> On 6/22/2016 10:47 AM, Digimer wrote:
> >This is called "fabric fencing" and was originally the only supported
> >option in the very early days of HA. It has fallen out of favour for
> >several reasons, but it does still work fine. The main issues is that it
> >leaves the node in an unclean state. If an admin (out of ignorance or
> >panic) reconnects the node, all hell can break lose. So generally power
> >cycling is much safer.
> 
> how is that any different than said ignorant admin powering up the
> shutdown node ?

On boot, the cluster software assumes it is "wrong" and doesn't connect
to any resources until it can verify state.

If the node is just disconnected and left running, and later
reconnected, it can try to write out (now old/incorrect) data to the
storage, corrupting things.

Speaking of shared storage, another fencing option is SCSI reservations.
It can be terribly finicky, but it can be useful.
-- 
Chris Adams <linux at cmadams.net>