RE: Migrating a 10TB VM from ESXi to PVE/Ceph

[Adam Thompson <athompso@athompso.net>]

I went with NFS precisely because FC storage isn't generally something PVE can mount - it's block storage, so it'll have (most likely) a VMFS5 filesystem and raw files with extents inside it, not VMDKs.  Pivoting through an NFS server flattens everything into a VMDK, which PVE can then mount and see and use.
-Adam

-----Original Message-----
From: Tom Weber <pve@junkyard.4t2.com> 
Sent: Monday, September 7, 2026 12:46 PM
To: pve-user@lists.proxmox.com
Subject: Re: Migrating a 10TB VM from ESXi to PVE/Ceph

Hi,

I'd try to make your FC SAN Storage visible to your PVE Cluster - so that it can "see" the .vmdk Files.

Next define a VM with the needed Hardware Settings (CPU, RAM, Network...) but small / empty Disks on your FC SAN Storage - choose VMDK Format.

This should give you a machine description in PVE (in /etc/pve/nodes/<NODE>/qemu-server/<ID>.conf) and vm-<ID>-disk-<x>.vmdk files on the FC SAN Storage.

Now with the VM shut down (in both worlds), you could rename the production VMDK Files to the vm-<ID>-disk-<x>.vmdk names used in the <ID>.conf file and you should be able to fire up the VM on the PVE cluster working with the vmware disks on the FC SAN (current Data).

Once the VM is running you could do a live migration (move Storage) of the VMDK disk to Ceph or whatever other PVE Storage.


 From time to time I did something similar and I dont see why it shouldn't work but please test and experiment with smaller VMs first - and if possible work with Snaphots/Backups whatever before mounting the production .vmdk files in PVE.

Regards,
   Tom


Am 07.09.26 um 09:08 schrieb Fabien Sirjean:
> Dear all,
> 
> After successfully migrating most of our infrastructure (300+ VMs) from VMware ESXi to PVE, we're struggling with one last critical VM: our BlueMind/Cyrus mail server (~800 users), with a 10TB virtual disk.
> 
> Our setup is:
> 
> Source: ESXi → Dell EMC VPLEX (FC) → Dell Unity
> Target: Proxmox VE → Ceph RBD (dedicated cluster)
> 
> We tried the Proxmox ESXi importer, but I/O performance degraded so much during the live import that the mail service could not sustain its normal workload.
> We then stopped the service to complete the migration, but the import eventually failed after almost 3 days, forcing us to start over.
> 
> Application-level migration/synchronization is not an option, so we're looking for a block/storage-level approach with minimal downtime.
> 
> Since the datastore ultimately resides on our FC SAN, could we bypass ESXi entirely and temporarily present the relevant VPLEX/Unity LUN to a PVE or migration host, mount/access the VMFS datastore read-only, and copy/convert the VMDK directly to Ceph RBD?
> Even better, is there a practical way to perform the bulk copy while the VM is running, then only synchronize the changed blocks during the final cutover?
> 
> Any advice or experience with direct VMFS access, VPLEX/Unity snapshots/clones, or other approaches for this kind of migration would be greatly appreciated.
> 
> Thanks!