Migrating a 10TB VM from ESXi to PVE/Ceph

[Fabien Sirjean <fsirjean@eddie.fdn.fr>]

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!