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September 12th, 2023 15:37

VxRail/vSAN, and DNS requirements with external VCenter

Infrastructure:
We are moving towards a 100% VxRail environment (not stretched), but are currently using an external VCenter on an legacy M1000chassis/VNX SAN array which are EOL and or nearing EOL.
This will be the last thing to migrate.
Both our DNS servers are now within one of the 5 VxRail clusters we are running, and all 5 clusters point to them.

History:
Our data center is, frankly, garbage, infrastructurally speaking and has suffered no less than 5 complete power outages in the last 3 years alone due to generator and UPS issues/repairs, doing totally dark. 2 were controlled downings, 3 were not.
They claim it's all repaired but I have serious trust issues now.

Issue: 
The even bigger concern right though is, I believe that vSAN, as per VMWare's docs, requires DNS to initialize, such as when a Vx Cluster is powered on after a sudden outage?
But if the DNS VM servers are dependent on vSAN, being inside a VxRail cluster, this creates a Catch-22;  how would I get the clusters back online w/o having the cluster running? 
Or is that wrong?
I'm hoping to get approval for an external rack server to run as a third secondary-type DNS server but so far no budgetary approval.  You can't make this stuff up.

Which is another question, is there a limit to the number of DNS servers that you can enter for a VxRail? All examples show no more than two, but I would prefer three if possible.

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September 13th, 2023 11:57

Hello lpphiggp,

Here is a link to a kb that maybe of assistance. https://dell.to/3sTCzzH

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September 13th, 2023 14:49

@Dell_Sam_L​ 
Thanks but nope.  That is a compat matrix between VxRail version and external VCenter,  which we're fine with.  The core of my question is whether VxRail vSAN requires DNS in order to boot back up in the event the entire cluster is powered down, nicely or otherwise.  The rest was details.
When I look in VCenter, at the Cluster level: Configure tab,  vSAN : Disk management, it lists the nodes by hostname, not IP.

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6.9K Posts

14-09-2023 05:15 PM

Hello lpphiggp,

You do need DNS in order to boot back up.

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September 20th, 2023 14:32

@Dell_Sam_L​ 

Thanks Sam,  that's what I was afraid of. 
What a silly system. It should just use IP, directly. Or at least provide that as an alternate option.
But that's VmWare's requirement for vSAN, not Dell's design, so I can't fault Dell/EMC.  
Anyone know VMWare's reasoning? 

(edited)

October 12th, 2023 19:09

The hosts themselves don't require DNS to boot. However, vCenter knows the hosts by their DNS name (in vCenter you have the choice to add hosts by IP or FQDN, but VxRail wants you to use the FQDN only).

So, when the vCenter comes up after a planned or unplanned outage, if DNS isn't resolving, the vCenter will flag the hosts as 'down' as it can't find them (by their FQDN).

The vSAN part of the VxRail doesn't require vCenter, so the data/storage side of the vSAN/VxRail cluster will work fine, but you may need to manually identify where your DNS servers are (which host) and power them up (from the ESXi host UIs), and then reboot the vCenter.

Long term, it's indeed easier to have a DNS server elsewhere too (e.g. other datacenter or a cloud-based solution).

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November 8th, 2023 13:58

For our VCF on VxRail deployments we also deploy a separate 2 node (PowerEdge with DAS) cluster that hosts it's own vCenter, 1 x domain controller (primarily for DNS), SFTP server (as a destination for VCF component file-based backups), RDS server (inc. some management tooling and a replicated copy of the password vault) and a few other bits and pieces, so if/when the VCF goes down we still have what we need to troubleshoot it (as well as shutdown/start-up with jumping through too many hoops).

The vSAN itself doesn't need DNS to come up though, we do have one environment without the off-host VMs/services and for that one you just need to power on the vSAN hosts, connect to the first host (where you should have pinned a domain controller and the vCenter) and power of the domain controller/DNS server. Once that's up then power on the vCenter and go from there, it's the vCenter that needs DNS rather than the hosts/vSAN.

(edited)

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