==== Resize SCSI LUN ====
/!\ Apply theses commands on each node of proxmox server
/!\ My physical disk is /dev/sdb, please adapt for your case
/!\ Remove VM or stop it before resize from Synology

  * Check the initial disk size

  lsblk

  * Resize the LUN in SCSI manager from Synology DSM
  * Rescan the volumes and check again the right size of physical disk

  iscsiadm --mode session --rescan 
  lsblk

  * Resize the physical volume

  pvresize /dev/sdb  

Enjoy !