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

[Adam Thompson <athompso@athompso.net>]

I migrated some very large (not quite as big as yours, only ~3TB) VMs by pivoting through a common NFS server.

Vmotion the VM to NFS.
Run the ESXi importer without any disks.
With the ESX VM shut down, manually attach the VMDKs from NFS.
Boot the VM under PVE.
Finally "move storage" in PVE.

Major downside: you need 2x or 3x the disk space.

I also used an offline variant of that with one PVE node acting as the NFS server, then "qm importdisk" locally on that node.

-Adam

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________________________________
From: Fabien Sirjean <fsirjean@eddie.fdn.fr>
Sent: Monday, 07 September 2026 02:08:23
To: pve-user@lists.proxmox.com <pve-user@lists.proxmox.com>
Subject: Migrating a 10TB VM from ESXi to PVE/Ceph

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!