[CentOS] KVM HA

[m.roth at 5-cent.us]

Digimer wrote:
> On 22/06/16 02:01 PM, Chris Adams wrote:
>> 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.
<snip>
>> 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.
>
> Close.
>
> The cluster software and any hosted services aren't running. It's not
> that they think they're wrong, they just have no existing state so they
> won't try to touch anything without first ensuring it is safe to do so.
<snip>
Question: when y'all are saying "reconnect", is this different from
stopping the h/a services, reconnecting to the network, and then starting
the services (which would let you avoid a reboot)?

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