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sunhux

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Can a VM vMotion or failover to another ESXi host in another cluster?

My customer only give me budget to set up 2 ESXi hosts only
(ie 2 physical servers only) but he has an existing cluster of
4 ESXi hosts (I suppose it's ESXi Ver 5 but I forgot to check).

I heard the rule of thumb is to have 5-6 hosts in a cluster so
that in the event 1 host fails, the remain 4-5 hosts will share
the load of this one server.  Having too many hosts in a
cluster also make it less manageable & cost-wise it's costlier.

The customer wanted the 2 ESXi hosts to be in a cluster by
itself but when one of the ESXi host fails, the VMs in it are
to auto-failover to ESXi hosts in another cluster?  Is this
possible?  What are the pre-requisites for this to take
place (ie must the ESXi version & patch level be the same?
must the server model of the 2-node cluster be the same
as the other cluster's hosts?  What about the datastore
requirements, network/port trunking/VLAN  etc etc ).


I heard that hosts within the same cluster must be of the
same server model (not even of different clock speed)
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Matt V
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It seems to me you should rethink the assumption that you need two separate clusters.  Two cluster is amost certain to be more complex and costly (due to inefficiencies) than one cluster of six hosts.  Here is a link to an article that refers a limit 8 hosts as an outdated guideline for VMWare.
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sunhux

ASKER

Thanks.

What's the difference between failover & vMotion: failover is not possible
between clusters while vMotion (if we share the same vCenter) is possible?
Is vMotion something that we do manually (ie "Migrate a VM" in vCenter?

In short, if I keep 2 separate clusters, I have to do it manually (ie vMotion)
while if they're in the same cluster, it can be 'automatic' (ie failover) ?
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ASKER

Also, what's the requirements for hosts/servers to be in the
same cluster?  

Q1:
Must they be of the same hardware model & clock speed?
Eg: we can't cluster IBM HX22 & HX21 together?  we can't
    cluster IBM x3650M2 & x3650M3 together?   Gee, if
    this is the case, when we plan to add additional ESXi
    host to the cluster in future & the hardware models
    got obsolete (& hdwre model can change every year),
    we have to upgrade all existing hosts to the same
    hardware model?  At least in the days I used OpenVMS
    cluster (from DEC), we could cluster different models
    of hardware together (VAX & VAX, Alpha & Alpha)

Q2:
Must they be using the same datastore (or is it the same
LUN) or same trunked VLAN?  What about individual
hosts' Management & vMotion IP address?  Must they
be in the same VLan/subnet?

Q3:
If they're in different clusters, any pre-requisites or
requirements as the above?
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ASKER

>cannot vMotion between datacenters
'Between datacenters' means the vMotion/Management IP addresses
of the ESXi hosts are on different subnets/VLANs (eg: 10.40.161.0 /24
& 10.40.166.0 /24) or it means the VMs on the different ESXi hosts
are on different subnets/VLans ?
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ASKER

>should rethink the assumption that you need two separate clusters.
I've already bought the 2 servers, say HX21 (while the other four
existing cluster's hosts are of lower end HX models),  then there's
no way I can cluster them together right?  Not an assumption
anymore but I'm now forced to work with 2 separate clusters or
there's still a chance to cluster them together?
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Missed one question:


Q2:
Must the ESXi hosts be using the same datastore (or the
same LUN) or same trunked VLAN?  What about individual
hosts' Management & vMotion IP address?  Must they
be in the same VLan/subnet?
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