On Fri, 19 Jun 2009, Derek J. Balling wrote:
On Jun 18, 2009, at 11:45 PM, Edward Ned Harvey wrote:
Not sure how much this will help, but - I barely see the point of
"migration" as it were.
One beautiful use of it is to migrate your VMs from HOST_A to HOST_B, upgrade
the firmware, install ESX patches, perform hardware maintenance on HOST_A,
etc., then migrate everything back. Repeat over the course of your entire
VMware farm.
ESX actually has, if you have DRS (Distributed Resource Scheduling) enabled,
the ability to, in conjunction with the Update Manager, figure out which ESX
hosts need updates, shuffle your running VMs to other servers, put the ESX
server in maintenance mode, upgrade it, reboot it, and when it comes back
online, bring it out of maintenance mode, and shuffle VMs back onto it so it
can proceed on to the next. In so doing, it can quickly - and without
customer impact - upgrade your entire cluster to the latest version of ESX,
say.
Migration is all about "zero downtime". Now that's not necessarily important
for every environment (in fact, we're in process of moving our web frontend
VMs to standalone ESXi hosts that don't have the enterprise licensing that
allows Vmotion, because it's architected such that "we can lose a ESX
server's worth of web servers without complaint" to do maintenance.
my big problem with live migration (especially as a disaster recovery
'solution') is that if the running machine dies it's too late to do a live
migration. If the application is important enough to need failover and
disaster recovery I need it to be able to survive a system just
disappearing, and so I need it to be able to recover on the new machine
without having the old machine available to migrate from, and if I have
that anyway, why not use that instead of live migration?
I can see live migration as being handy for maintinance and planned
changes, but it's not _that_ hard to plan to do the failover at off-peak
times when a few seconds of outage aren't a problem.
David Lang
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