Virtual Disk Development Kit Release Notes

Release date: 3 MAY 2018 | Builds: ESXi 8294253, VDDK 8315684
VDDK 6.5.3 for vSphere 6.5 U2 | Last document update: 23 JAN 2019
Check frequently for additions and updates to these release notes.


About the Virtual Disk Development Kit

The Virtual Disk Development Kit (VDDK) 6.5.3 is a bug-fix release to support vSphere 6.5 U2.

VDDK is used with vSphere Storage APIs for Data Protection (VADP) to develop backup and restore software. For general information about this development kit, how to obtain the software, programming details, and redistribution, see the VDDK documentation landing page.

VDDK 6.5.3 supports the same set of operating systems to perform proxy backup as VDDK 6.5.1, with the addition of Windows Server 2016 version 1709.

Changes and New Features

This release contains bug fixes but no new features.

Compatibility Notices

This VDDK release should be forward compatible with the next major vSphere release.

ESXi hosts and especially vCenter Server should be upgraded in conjunction with VDDK libraries.

Recently Resolved Issues

The VDDK 6.5.3 release resolves the following issues.

  • Backup fails when snapshot cannot be HotAdded to CBRC enabled proxy VM

    If the proxy VM and a target Windows VM are enabled for content based read cache (CBRC), with a quiesced snapshot, HotAdd backup fails because when the quiesced snapshot cannot be added to the proxy VM. This is because the digest of the snapshot disk is disabled in the target VM, so reconfiguration fails because the digest is missing only for the snapshot. The cause is a code change made to fix a bug in ESXi 5.0, before VDDK supported CBRC. VDDK 6.5 and later support CBRC-enabled VMs, so the digest disk should be enabled during application-quiesced snapshot creation on Wndows. The digest is enabled in this release, so HotAdd backup can succeed.

  • Could not connect directly to ESXi on IPv6 networks.

    After connecting to an ESXi host with VixDiskLib_Connect(Ex) in NBD(SSL) mode on an IPv6 network, opening virtual disk with VixDiskLib_Open throws this error: “Host address lookup for server (null) failed: No such host is known.” NBD(SSL) connection to vCenter Server work, as does HotAdd mode. The IPv6 issue is fixed in this release.

  • Memory leaks in vixDiskLib and NFC code.

    Several memory leaks (caused by failure to free memory objects) were fixed for this release.

  • Observed intermittent hang during disk open.

    During backup, the error message “GLib-GObject: g_object_unref: assertion G_IS_OBJECT (object)” was occasionally seen, repeating due to a main loop. This was fixed by adding timeouts for get NFC ticket, get file name, and prepare for access.

  • Log file entries related to blacklist are missing in VDDK 6.5.

    Log file entries (at the verbose and trivial levels) related to device blacklisting are missing in VDDK 6.5 and 6.5.1 as compared to VDDK 6.0. This issue was fixed in the 6.5.2 release for vCloud, and in this 6.5.3 release.

Known Issues and Workarounds

The VDDK 6.5 release had the following issues, which persist in VDDK 6.5.3, but are fixed in subsequent releases.

  • Maximum 25 NFC sessions with ESXi 6.5 hosts.

    In early 6.5 releases of ESXi, including 6.5 U2, the number of NFC sessions is limited to 25, due to a lowered thread count limit. This issue reduces the concurrency of NBD backups to 25 from 48, as originally claimed for vSphere 6. Upgrading to ESXi 6.7 is one solution. Updating VDDK does not help. This issue will be fixed in ESXi hosts delivered in the vSphere 6.5 U3 release.

  • HotAdd proxy failure with Windows Server backups

    If there is SATA controller in the Windows backup proxy, HotAdd mode might not work. The cause is that VDDK does not rescan SATA controllers after HotAdding, so if there exist multiple SATA controllers or ACHI controllers, VDDK might use the wrong controller ID and fail to find the HotAdded disk. Disk open fails, resulting in “HotAdd ManagerLoop caught an exception” and “Error 13 (You do not have access rights to this file)” errors. The workaround in this case is to remove the SATA controller from the Windows backup proxy. A fix was found and is provided in the 6.7.1 release. See KB 2151091.

  • Virtual disks must be offline for HotAdd restore.

    The Virtual Disk Programming Guide used to recommend SAN policy OnlineAll for Windows 2008 and later. This recommendation was removed for the VDDK 6.5.1 release. Disk online may cause signature collision problems and restore problems. For HotAdd transport, VMware suggests customers running Windows 2008 R2 or later set SAN policy to OfflineShared or OfflineAll.

For VDDK issues that were resolved before the vSphere 6.5.3 release, see the VDDK 6.5.x Release Notes.