[Info-vax] VMware

[Grant Taylor]

On 12/10/19 5:05 AM, Bob Gezelter wrote:
> However useful VM migration, it is not a functional replacement for 
> OpenVMS clusters. VM migration allows controlled workload migration, 
> in the event of an uncontrolled system failure, e.g. complete 
> power-failure without warning or system destruction. migration will 
> not have sufficient time to execute a migration.

I don't completely agree with this.

VMware has a High Availability mode where the same VM / system image is 
running concurrently on multiple disparate physical hosts.  One of which 
will be connected to the outside world.  The other is disconnected and 
receiving real time updates from the first.  As in VMware is replicating 
memory, processor, and disk state near real time.  This means that when 
one physical host falls out of the rack, the other physical host takes 
over and continues running the VM with the exception that it is now 
master and the VM is connected to the world.  As such, even established 
network connections continue on the alternate physical host.

VMware has, and apparently other hypervisors have, the ability to move 
running VMs from one host to another host in a manner that is almost 
unperceptible to clients.  Packets don't drop.  They may have a slight 
increase in latency /during/ the transition.  But it really looks like a 
momentary congestion in a router buffer somewhere.



-- 
Grant. . . .
unix || die