45871: Acronis Backup for VMware 9: "The specified delta disk format 'redoLogFormat' is not supported." error in vSphere 5.5

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Last update: 13-03-2017


  1. You install Acronis Backup for VMware 9 as a Virtual Appliance onto an ESXi 5.5 host
  2. In the vSphere events of the Virtual Appliance you see "The specified delta disk format 'redoLogFormat' is not supported." error.
  3. The backup is slower than usual


The problem is that in vSphere 5.5 there was a new format introduced for the snapshot delta disks which is unsupported by older virtual hardware version: http://www.vmware.com/files/pdf/techpaper/SEsparse-vsphere55-perf.pdf


  1. Turn off Acronis vmProtect Virtual Appliance
  2. Right click on it in vSphere client and choose "Upgrade Hardware" option
  3. Turn on Acronis vmProtect Virtual Appliance

More information

Due to the error the virtual disks are opened in NBD (network) mode and thus the backup performance my be impacted. It is recommended to apply the above solution for all virtual appliances deployed to ESXi 5.5 hosts.