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Can we run ESXi 5.1 with ESXi 6?

vmich
vmich asked
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We have 4 host running ESXi 5.1 and we need to add another host and we can only get ESXi 6 now. Would it be ok to run the 1 host with ESXi 6 in the cluster with the 4 others with ESXi 5.1 or should we just upgrade all of them to ESXi 6?
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Paul SolovyovskySenior IT Advisor
Top Expert 2008

Commented:
If you're running vCenter you would need to upgrade vCenter (including SSO which is now part of PSC, as well as a few more upgrade with vCenter).  Otherwise you can run a mixed cluster with 5.x and 6
John SalleSenior IT Systems Engineer

Commented:
If you're referring to the free version of ESXi, you can still download 5.1 from here: https://my.vmware.com/group/vmware/evalcenter?p=free-esxi5
VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017
Commented:
You will need to upgrade your vCenter Server 5.1 to 6.0.

Easy to do, just insert the vCenter Server 6.0 DVD/ISO, and run the setup. (if using vCenter Server for WIndows)

However, you may want to check your database size, if you are using the vCenter Server for Windows and SQL Express, because it's likely with that many hosts you will be getting close to the 10GB database maximum size with SQL Express.

and you may be better off using the vCenter Server Appliance.

(you can downgraded your licenses to 6.0 from 5.1!)

Author

Commented:
Andrew,
So if we upgrade the vcenter to version 6 then we could add the new host with esxi 6 and then leave the others at ESXi 5.1?
John SalleSenior IT Systems Engineer
Commented:
Yes you can do that. vCenter needs to be the same version as your highest host, but it's backwards compatible. So if you have a single host with ESXi 6, vCenter needs to be ESXi 6. Then you can either leave your 5.1 hosts or upgrade them as well.
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017

Commented:
Andrew,
So if we upgrade the vcenter to version 6 then we could add the new host with esxi 6 and then leave the others at ESXi 5.1?

Yes

Author

Commented:
esxi 6 running with esxi 5.1