Add Host to pool, is this non-destructive to local VM's?



  • I have (2) XCP-NG 8.0 servers each running in their own pool (standalone). I would like to non-destructively add the second server into the pool of the first. Each host currently has a local SR with active VM's. I am implementing a new ISCSI SAN and need to get these hosts put in a single pool. I see where to do this in Xen Orchestra but just wanted to confirm before attempting this.

    I have read some information that says adding or removing a host to/from a pool will "reset" the host back to a fresh install state and wipe all VM's from the host. I would like to confirm if this is still true on 8.0 or if that was the case on an older version.

    My goal is to have a couple of VM's stay running on the existing local SR while selectively migrating VM's to the ISCSI SR. I am not ready to move all to shared storage at this time. I am aware of the impact that has for HA and this limitation, it is only temporary.

    If someone can confirm the functionality it would be appreciated. Is it a best practice to shutdown the VM's on the host before joining it to another pool? I do plan to have full backups in place before attempting this move.
    Will removing a host from a pool destroy any VM's running off the local SR?

    Any feedback is appreciated.



  • That is correct. My recommendation would be to migrate the VMs from one host to the other, then wipe that host and bring it into the pool (or just bring it into the pool). I'm not sure it wipes the actual data of those VMs off the local storage repository; but, it will certainly clear out the metadata of all the VMs on that host. You can't recover that metadata into a pool that I'm aware of.



  • Thanks for the feedback.

    "We're going to need a bigger boat" unfortunately both hosts are fairly utilized and host A cannot take on the load of host b even temporarily.
    If what you say is the case my only option would be to add a new empty host (host C) to the pool, add the shared storage to the pool of two, migrate VM's from host B to new host C so all VM's are vacated from it and lastly add host B to the pool.



  • Yes. That would be a way of doing so. If you can afford the downtime, you could also use a backup solution (XOA, Alike DR, etc.) to backup the VMs from both hosts, build the pool from scratch using both hosts in a clean state, and then restore back into the new pool (this way gives you a chance to not only start fresh; but, implement any big "lessons learned" or "new ideas" you've got on your list).


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