=head1 NAME

nbdkit-vddk-plugin - nbdkit VMware VDDK plugin

=head1 SYNOPSIS

 nbdkit vddk [[file=]FILENAME | export=WILDCARD]
             [compression=none|zlib|fastlz|skipz]
             [config=FILENAME] [cookie=COOKIE]
             [create=true] [create-adapter-type=ide|scsi-buslogic|...]
             [create-hwversion=workstation4|workstation5|...]
             [create-size=...] [create-type=monolithic-sparse|...]
             [libdir=LIBRARY] [nfchostport=PORT]
             [password=PASSWORD | password=- | password=+FILENAME |
              password=-FD]
             [port=PORT] [server=HOSTNAME]
             [single-link=true] [snapshot=MOREF]
             [thumbprint=THUMBPRINT] [transports=MODE:MODE:...]
             [unbuffered=true] [user=USERNAME] [vm=moref=ID]
 nbdkit vddk --dump-plugin

=head1 DESCRIPTION

C<nbdkit-vddk-plugin> is an L<nbdkit(1)> plugin that serves disks from
local VMware VMDK files, VMware ESXi servers, VMware VCenter servers,
and other sources.

It requires VMware's proprietary VDDK library that you must download
yourself (see L</LIBRARY LOCATION> below).

For an easy-to-use wrapper around this plugin which automates setting
things up to connect to a remote VMware server, see:
L<https://gitlab.com/nbdkit/vddk-remote>

=head1 EXAMPLES

=head2 Open a local VMDK file

 $ nbdkit vddk libdir=/opt/vmware-vix-disklib-distrib \
               /absolute/path/to/file.vmdk
 $ nbdinfo --size nbd://localhost
 10485760
 $ nbdcopy nbd://localhost outputfile.raw

Open F<file.vmdk> with this plugin, and use L<nbdinfo(1)> and
L<nbdcopy(1)> to inspect and copy out the data.  When opening local
files the filename B<must> be an absolute path.

The C<libdir> parameter points to the location of VDDK, see
L</LIBRARY LOCATION> below.  In the examples below it is omitted for
brevity.

=head2 Create a new local VMDK file

You can use VDDK to create a VMDK file and fill it with the contents
of a disk image.  Note the C<create-size> parameter is the virtual
size of the final VMDK disk image and must be at least as large as the
input disk:

 nbdkit vddk \
        /absolute/path/to/output.vmdk \
        create=true create-size=100M \
        --run 'qemu-img convert input.qcow2 $uri'

=head2 Open a file on a remote VMware ESXi hypervisor

Connect directly to a VMware ESXi hypervisor and export a particular
file:

 nbdkit vddk user=root password=+/tmp/rootpw \
             server=esxi.example.com thumbprint=xx:xx:xx:... \
             vm=moref=2 \
             "[datastore1] Fedora/Fedora.vmdk"

C<user> and C<password> must be specified.  Use C<password=+FILENAME>
to provide the password securely in a file.

C<server> is the hostname of the ESXi server.

C<thumbprint> is the thumb print for validating the SSL certificate.
How to find the thumb print of a server is described in
L</THUMBPRINTS> below.

C<vm> is the Managed Object Reference ("moref") of the virtual
machine.  See L</MANAGED OBJECT REFERENCE> below.

The file parameter is the file you want to open, usually in the form
S<C<"[datastore] vmname/vmname.vmdk">>.  See L</FILE PARAMETER> below.

=head2 Open a file on a remote VMware vCenter server

Connect via VMware vCenter and export a particular file:

 nbdkit vddk user=root password=vmware \
             server=vcenter.example.com thumbprint=xx:xx:xx:... \
             vm=moref=vm-16 \
             "[datastore1] Fedora/Fedora.vmdk"

C<user> and C<password> must be specified.  Use C<password=+FILENAME>
to provide the password securely in a file.

C<server> is the hostname of the vCenter server.

C<thumbprint> is the thumb print for validating the SSL certificate.
How to find the thumb print of a server is described in
L</THUMBPRINTS> below.

C<vm> is the Managed Object Reference ("moref") of the virtual
machine.  See L</MANAGED OBJECT REFERENCE> below.

The file parameter is the file you want to open, usually in the form
S<C<"[datastore] vmname/vmname.vmdk">>.  See L</FILE PARAMETER> below.

=head2 Allow the client to choose the filename

As the previous example, but allow the client to choose which file to
serve, using the C<export=WILDCARD> parameter:

 nbdkit vddk user=root password=vmware \
             server=vcenter.example.com thumbprint=xx:xx:xx:... \
             vm=moref=vm-16 \
             export='\[datastore1\] Fedora/*.vmdk'

The client now picks the specific filename, as long as it matches the
wildcard given on the nbdkit command line.  For example:

 $ nbdsh
 nbd> h.set_export_name("[datastore1] Fedora/Fedora.vmdk")
 nbd> h.connect_tcp("localhost", "nbd")

or the same using an NBD URI with usual URL encoding:

 nbdinfo 'nbd://localhost/%5bdatastore1%5d%20Fedora/Fedora.vmdk'

=head1 PARAMETERS

For opening a local VMDK file, the C<file> parameter is required and
must be an absolute path.

For opening a remote connection, C<server>, C<thumbprint>, C<user>,
C<password> and C<vm> are required.  Either C<file> or C<export> are
required.

All other parameters are optional.

=over 4

=item B<compression=none>

=item B<compression=zlib>

=item B<compression=fastlz>

=item B<compression=skipz>

(nbdkit E<ge> 1.24, vSphere E<ge> 6.5)

Select the compression type used over the network between VDDK and the
VMware server.  The default is C<none>.  See VMware document “Best
Practices for NBD Transport”.

=item B<config=>FILENAME

The name of the VDDK configuration file.

The config file controls rarely adjusted VDDK settings like log level,
caching and timeouts.  See the VDDK documentation for a full list of
settings.

VDDK itself looks in a few default locations for the configuration
file, usually including F</etc/vmware/config> and
F<$HOME/.vmware/config>.  Using C<config> overrides these defaults.

=item B<cookie=>COOKIE

(vSphere E<ge> 6.7)

Cookie from existing authenticated session on the host.

This changes the authentication type from C<VIXDISKLIB_CRED_UID> to
C<VIXDISKLIB_CRED_SESSIONID> which can improve performance.  The
cookie can be found by connecting to a VCenter Server over HTTPS and
retrieving the C<vmware_soap_session> cookie.

=item B<create=true>

(nbdkit E<ge> 1.30)

Create a new, local VMDK file.  Instead of opening an existing VMDK
file, a new VMDK file is created and opened.  The filename is given by
the C<file> parameter (see below).  The file must not exist already.
It is not possible to create a remote file using nbdkit.

If this is used, the C<create-size> parameter is required to specify
the virtual size of the disk.  Other C<create-*> parameters (see
below) can be used to control the VMDK sub-format.

=item B<create-adapter-type=ide>

=item B<create-adapter-type=scsi-buslogic>

=item B<create-adapter-type=scsi-lsilogic>

(nbdkit E<ge> 1.30)

Specify the VMDK disk adapter type.  The default is C<scsi-buslogic>.

=item B<create-hwversion=workstation4>

=item B<create-hwversion=workstation5>

=item B<create-hwversion=workstation6>

=item B<create-hwversion=esx30>

=item B<create-hwversion=esx4x>

=item B<create-hwversion=esx50>

=item B<create-hwversion=esx51>

=item B<create-hwversion=esx55>

=item B<create-hwversion=esx60>

=item B<create-hwversion=esx65>

=item B<create-hwversion=>N

(nbdkit E<ge> 1.30)

Specify the VMDK virtual hardware version.  You can give either the
named version or the equivalent 16 bit number.

The default is C<workstation5> (N = 4).

=item B<create-size=>SIZE

(nbdkit E<ge> 1.30)

Specify the virtual size of the created disk.  The C<SIZE> can use
modifiers like C<100M> etc.  It must be a multiple of 512 bytes
because VMware only supports sector sizes.

If you use C<create=true> then this parameter is required.

=item B<create-type=monolithic-sparse>

=item B<create-type=monolithic-flat>

=item B<create-type=split-sparse>

=item B<create-type=split-flat>

=item B<create-type=vmfs-flat>

=item B<create-type=stream-optimized>

=item B<create-type=vmfs-thin>

=item B<create-type=vmfs-sparse>

(nbdkit E<ge> 1.30)

Specify the VMDK sub-format.  The default is C<monolithic-sparse>.

Some VMDK sub-formats use multiple files, where the C<file> parameter
specifies the "Disk Descriptor File" and the disk contents are stored
in adjacent files.

=item B<export=>WILDCARD

(nbdkit E<ge> 1.44)

For remote connections, allow the client to choose which file to
serve, using the NBD protocol export name.  The export name must match
C<WILDCARD>.  This is an alternative to specifying a single, exact
filename, see C<file> below.

C<[> and C<]> are special characters in wildcards and must be escaped
as C<\[> and C<\]>.  In addition you may have to quote the whole
wildcard to protect it from the shell.

The wildcard provides some security, but it is unwise to allow
untrusted clients to connect when using this option.

=item [B<file=>]FILENAME

=item [B<file=>]B<[>datastoreB<] >vmnameB</>vmnameB<.vmdk>

Set the name of the VMDK file to serve.

For local files you B<must> supply an absolute path.
For remote files see L</FILE PARAMETER> section below.

C<file=> __IS_MAGIC__

=item B<libdir=>PATHNAME

This sets the path of the VMware VDDK distribution.

VDDK uses this to load its own plugins, if this path is unspecified or
wrong then VDDK will work with reduced functionality.  See
L</LIBRARY LOCATION> below.

=item B<nfchostport=>PORT

Port used to establish an NFC connection to ESXi.  Defaults to 902.

=item B<password=>PASSWORD

Set the password to use when connecting to the remote server.

Note that passing this on the command line is not secure on shared
machines.

=item B<password=->

Ask for the password (interactively) when nbdkit starts up.

=item B<password=+>FILENAME

Read the password from the named file.  This is a secure method
to supply a password, as long as you set the permissions on the file
appropriately.

=item B<password=->FD

Read the password from file descriptor number C<FD>, inherited from
the parent process when nbdkit starts up.  This is also a secure
method to supply a password.

=item B<port=>PORT

The port on the VCenter/ESXi host.  Defaults to 443.

=item B<server=>HOSTNAME

The hostname or IP address of VCenter or ESXi host.

=item B<single-link=true>

(nbdkit E<ge> 1.12)

Open the current link, not the entire chain.  This corresponds to the
C<VIXDISKLIB_FLAG_OPEN_SINGLE_LINK> flag.

=item B<snapshot=>MOREF

The Managed Object Reference of the snapshot.
See L</MANAGED OBJECT REFERENCE> below.

=item B<thumbprint=>THUMBPRINT

The SSL (SHA1) thumbprint for validating the SSL certificate.

The format is
C<xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx>
(20 hex digit pairs).

See L</THUMBPRINTS> below for how to get this.

=item B<transports=>MODEB<:>MODEB<:>...

List of one or more transport modes to use.  Possible values include
‘nbd’, ‘nbdssl’, ‘san’, ‘hotadd’, ‘file’ (see L</DUMP-PLUGIN OUTPUT>
below).  If not given, VDDK will try to choose the best transport
mode.

=item B<unbuffered=true>

(nbdkit E<ge> 1.12)

Disable host caching.  This corresponds to the
C<VIXDISKLIB_FLAG_OPEN_UNBUFFERED> flag.

=item B<user=>USERNAME

The username to connect to the remote server as.

=item B<vm=moref=>ID

The Managed Object Reference ("moref") of the virtual machine.
See L</MANAGED OBJECT REFERENCE> below.

=item B<vimapiver=>APIVER

This parameter is ignored for backwards compatibility.

=back

=head1 LIBRARY LOCATION

The VDDK library should B<not> be placed on a system library path such
as F</usr/lib>.  The reason is that the VDDK library ships with
recompiled libraries like F<libcrypto.so> and F<libstdc++.so> that
conflict with system libraries.

You have two choices:

=over 4

=item *

Place VDDK in the default libdir which is compiled into this plugin,
for example:

 $ nbdkit vddk --dump-plugin | grep ^vddk_default_libdir
 vddk_default_libdir=/usr/lib64/vmware-vix-disklib

=item *

But the best advice is to unpack the VDDK tarball anywhere you like
and set the C<libdir=/path/to/vmware-vix-disklib-distrib>.  For
example:

 nbdkit vddk \
        libdir=/opt/vmware-vix-disklib-distrib \
        /path/to/file.vmdk

=back

=head2 No need to set C<LD_LIBRARY_PATH>

In nbdkit E<le> 1.16 you had to set the environment variable
C<LD_LIBRARY_PATH> when using this plugin.  In nbdkit E<ge> 1.18 this
is I<not> recommended.

=head1 SUPPORTED VERSIONS OF VDDK

=over 4

=item VDDK E<ge> 6.7 (released Apr 2018)

This is the minimum version of VDDK supported.  Older versions will
not work.

This is also the first version that supported the
C<VixDiskLib_QueryAllocatedBlocks> API.  This is used to provide
sparseness (extent) information over NBD.

=item VDDK 9.0.1.0 (released Sep 2025)

This is the latest version of VDDK that we have tested at the time of
writing, but the plugin should work with future versions.

=back

This plugin is only supported on the x86-64 architecture.

=head1 FILE PARAMETER

The C<file> parameter can either be a local file, in which case it
must be the absolute path.  Or it can refer to a remote file on the
VMware server in the format S<C<"[datastore] vmname/vmname.vmdk">>.

=head2 Finding the remote filename

For remote files you can find the path using L<virsh(1)>.  For ESXi:

 $ virsh -c 'esx://esxi.example.com?no_verify=1' dumpxml guestname
 ...
  <disk type='file' device='disk'>
    <source file='[datastore] vmname/vmname.vmdk'/>
 ...

For vCenter the command is the same but the URI starts with C<vpx://>:

 $ virsh -c 'vpx://vcenter.example.com/Datacenter/esxi.example.com?no_verify=1' \
         dumpxml guestname

See also: L<https://libvirt.org/drvesx.html>

=head2 Optional file= prefix

The C<file=> part is optional, so these commands are equivalent:

 nbdkit vddk file=/path/to/file.vmdk
 nbdkit vddk /path/to/file.vmdk

=head2 Relationship to the C<export> parameter

Instead of C<file>, you can use the C<export=WILDCARD> parameter to
allow the client to choose the filename, as long as it matches the
given wildcard.

=head1 THUMBPRINTS

The thumbprint is a 20 byte string containing the SSL (SHA1)
fingerprint of the remote VMware server and it is required when making
a remote connection.  There are several ways to obtain this.

=head2 Using a web browser

Visit C<https://SERVER-NAME/folder> and log in.  Click the lock icon
next to the URL bar and navigate to the SHA-1 fingerprint of the
site’s certificate.  This 20 hex digit pair string can be directly
copied to the C<thumbprint=> parameter.

=head2 Using openssl remotely

The following command will print the thumbprint of a VMware server
called C<SERVER-NAME>:

 $ openssl s_client -connect SERVER-NAME:443 </dev/null |
   openssl x509 -in /dev/stdin -fingerprint -sha1 -noout

=head2 By logging in to the ESXi or vCenter server

Log in to the ESXi hypervisor shell and run this command:

 # openssl x509 -in /etc/vmware/ssl/rui.crt -fingerprint -sha1 -noout

For VMware vCenter servers the thumbprint is printed on the text
console of the server or is available by logging in to the server and
using this command:

 # openssl x509 -in /etc/vmware-vpx/ssl/rui.crt -fingerprint -sha1 -noout

=head2 Trick: Get VDDK to tell you the thumbprint

Another way to get the thumbprint of a server is to connect to the
server using a bogus thumbprint with debugging enabled:

 nbdkit -fv vddk server=esxi.example.com [...] thumbprint=12 \
        --run 'qemu-img info "$uri"'

The nbdkit process will try to connect (and fail because the
thumbprint is wrong).  However in the debug output will be a message
such as this:

 nbdkit: debug: VixDiskLibVim: Failed to verify SSL certificate: actual thumbprint=B2:31:BD:DE:9F:DB:9D:E0:78:EF:30:42:8A:41:B0:28:92:93:C8:DD expected=12

This gives you the server’s real thumbprint.  Of course this method is
not secure since it allows a Man-in-the-Middle (MITM) attack.

=head1 MANAGED OBJECT REFERENCE

Some use cases require you to pass in the Managed Object Reference
("moref") of an object on the VMware server.

For VMware ESXi hypervisors, the C<vm> moref is a number
(eg. C<vm=moref=2>).  For VMware VCenter it is a string beginning with
C<"vm-">) (eg. C<vm=moref=vm-16>).  Across ESXi and vCenter the
numbers are different even for the same virtual machine.

If you have libvirt E<ge> 3.7, the moref is available in the
L<virsh(1)> C<dumpxml> output:

 $ virsh -c 'esx://esxi.example.com?no_verify=1' dumpxml guestname
 ...
 <vmware:moref>2</vmware:moref>
 ...

or:

 $ virsh -c 'vpx://vcenter.example.com/Datacenter/esxi.example.com?no_verify=1' \
       dumpxml guestname
 ...
 <vmware:moref>vm-16</vmware:moref>
 ...

An alternative way to find the moref of a VM is using the
C<moRefFinder.pl> script written by William Lam
(L<http://www.virtuallyghetto.com/2011/11/vsphere-moref-managed-object-reference.html>
L<https://blogs.vmware.com/vsphere/2012/02/uniquely-identifying-virtual-machines-in-vsphere-and-vcloud-part-2-technical.html>).

=head1 DUMP-PLUGIN OUTPUT

To query more information about the plugin (and whether it is
working), use:

 nbdkit vddk --dump-plugin

or:

 nbdkit vddk --dump-plugin libdir=/opt/vmware-vix-disklib-distrib

(see L</LIBRARY LOCATION> above).

If the plugin is not present or not working you will get an error.

If it works the output will include:

=over 4

=item C<vddk_default_libdir=...>

The compiled-in library path.  Use C<libdir=PATHNAME> to override this
at runtime.

=item C<vddk_has_nfchostport=1>

If this is printed then the C<nfchostport=PORT> parameter is supported
by this build.

=item C<vddk_library_version=...>

The VDDK major library version: 6, 7, 8, ...
If this is omitted it means the library could not be loaded.

=item C<vddk_dll=...>

Prints the full path to the VDDK shared library.  Since this requires
a glibc extension it may not be available in all builds of the plugin.

=item C<vddk_transport_modes=...>

Print the list of transport modes supported by VDDK.  This is a
colon-separated list such as C<file:san:hotadd:nbdssl:nbd>

This is the default set of transport modes that are tried in turn,
unless you override the list using the C<transports=...> parameter.

=item C<VixDiskLib_...=1>

For each VDDK API that the plugin uses I<and> which is present in the
VDDK library that was loaded, we print the name of the API
(eg. C<VixDiskLib_Open=1>).  This lets you see which optional APIs are
available, such as C<VixDiskLib_Flush> and
C<VixDiskLib_QueryAllocatedBlocks>.  If the library could not be
loaded then these lines are not printed.

=back

=head1 NOTES

=head2 Sector size limitation

The VDDK plugin can only answer read/write requests on whole 512 byte
sector boundaries.  This is because the VDDK Read and Write APIs only
take sector numbers.  If your client needs finer granularity, you can
use L<nbdkit-blocksize-filter(1)>:

 nbdkit vddk ... --filter=blocksize minblock=512

=head2 FileLockCreateEntryDirectory errors

When opening a local VMDK file, VDDK needs to create a lock file in
the same directory.  The directory must be writable otherwise you will
see errors like:

 nbdkit: vddk[1]: error: FILE: FileLockCreateEntryDirectory creation
 failure on '/absolute/path/to/file.vmdk.lck': Permission denied

The solution is to either make the directory / filesystem writable; or
open the file read-only by adding the nbdkit I<-r> option:

 nbdkit -r vddk /absolute/path/to/file.vmdk

=head2 Out of memory errors

In the verbose log you may see errors like:

 nbdkit: vddk[3]: error: [NFC ERROR] NfcFssrvrProcessErrorMsg:
 received NFC error 5 from server: Failed to allocate the
 requested 2097176 bytes

This seems especially common when there are multiple parallel
connections open to the VMware server with large NBD reads and writes.

=head3 Increase resource limits on the server

The error above can be caused by resource limits set on the VMware
server.  You can increase the limit for the NFC service by editing
F</etc/vmware/hostd/config.xml> and adjusting the
C<E<lt>maxMemoryE<gt>> setting:

 <nfcsvc>
   <path>libnfcsvc.so</path>
   <enabled>true</enabled>
   <maxMemory>50331648</maxMemory>
   <maxStreamMemory>10485760</maxStreamMemory>
 </nfcsvc>

and restarting the C<hostd> service:

 # /etc/init.d/hostd restart

For more information see L<https://bugzilla.redhat.com/1614276>.

=head3 Limit request sizes

In addition, or as an alternative to adjusting the server
configuration, you can use L<nbdkit-blocksize-filter(1)> to limit the
maximum request size.  By default this plugin translates NBD requests
directly into VDDK requests, and it appears that very large VDDK
requests can cause the error seen above.

Using:

 nbdkit vddk ... --filter=blocksize minblock=512 maxdata=2M

will cause nbdkit to automatically split and combine requests so that
VDDK sees only sizes in the range C<[512..2M]>.

=head2 Error 1 (Unknown error) when opening a disk

Opening a disk fails with an error like:

 nbdkit: vddk[1]: debug: VixDiskLib: VixDiskLib_OpenEx:
 Cannot open disk <name>. Error 1 (Unknown error) at <line>.

This common and totally useless error message can be printed by VDDK
for lots of reasons.  B<Make sure debugging is enabled> and look at
any debug messages printed before this to find out what is really
going on.  Common reasons are listed below.

=head3 The thumbprint parameter is wrong

Verify whether the C<thumbprint> parameter matches the SHA1
fingerprint of the remote VMware server.  See L</THUMBPRINTS> above
for how to set this correctly.

=head3 The guest is using an "Independent" mode disk

In debugging output you will see messages including:

 GetFileName: Cannot create disk spec for disk <name>.
 Error occurred when obtaining the file name for <name>.

If the Disk Mode is "Independent-Persistent" or
"Independent-Nonpersistent", then S<VDDK E<ge> 7> has a bug where it
cannot open these disks.  The only known workarounds are to use S<VDDK
E<le> 6.7>, or to change the Disk Mode to a regular dependent disk.

=head2 Troubleshooting performance problems

VDDK has very uneven performance with some operations being very slow.
This plugin has options to allow you to debug performance issues.  If
your application has a debug or diagnostic setting, add the following
nbdkit command line options:

 -v -D nbdkit.backend.datapath=0 -D vddk.datapath=0 -D vddk.stats=1

C<-v> enables verbose messages and the two datapath options I<disable>
the very verbose per-read/-write messages.  C<-D vddk.stats=1> enables
a summary when nbdkit exits of the cumulative time taken in each VDDK
function, the number of times each function was called, and (for read
and write) the number of bytes transferred.  An example of what those
stats look like can be found here:
L<https://gitlab.com/nbdkit/nbdkit/-/commit/5c80f0d290db45a679d55baf37ff39bacb8ce7ec>

You can interpret the stats as follows:

=over 4

=item C<Read>

The cumulative time spent waiting for VDDK to return from
C<VixDiskLib_Read> calls, the number of times this function was
called, and the total bytes read.  You can use this to determine the
read bandwidth to the VMware server.

=item C<Write>

=item C<Flush>

Same as above, but for writing and flushing writes.

=item C<ReadAsync>

=item C<WriteAsync>

Same as above, but for asynchronous read and write calls introduced in
S<nbdkit 1.30>.

=item C<QueryAllocatedBlocks>

This call is used to query information about the sparseness of the
remote disk.  It is only available in VDDK E<ge> 6.7.  The call is
notably very slow in all versions of VMware we have tested.

=item C<Open>

=item C<Close>

=item C<ConnectEx>

=item C<Disconnect>

=item C<InitEx>

=item C<Exit>

The cumulative time spent connecting and disconnecting from the VMware
server, which can also be very slow.

=back

=head2 Failure to load libssl.so.3 on RHEL 8

With VDDK E<ge> 8.0.2 on Red Hat Enterprise Linux 8:

 nbdkit: error: libssl.so.3: cannot open shared object file:
 No such file or directory

This is a bug in VDDK.  The workaround is to use VDDK 8.0.1.
See also: L<https://issues.redhat.com/browse/RHEL-28533>

=head2 Extents information may not be reliable for local VMDK files

The underlying C<QueryAllocatedBlocks> call which we use to return
extents information does not seem to work reliably for local VMDK
files, often returning wildly incorrect information such as showing
allocated files to be completely sparse.  This can affect
sparseness-aware tools like L<nbdcopy(1)>.  If you see this you can
ignore sparseness information by adding I<--filter=noextents> on the
nbdkit command line (see L<nbdkit-noextents-filter(1)>).

=head1 DEBUG FLAGS

Debugging messages can be very helpful if you have problems connecting
to VMware servers, or to find the list of available transport modes,
or to diagnose SAN problems:

 nbdkit -f -v vddk file=FILENAME [...]

Additional debug flags are available:

=over 4

=item B<-D vddk.diskinfo=1>

Debug disk information returned by C<GetInfo>.

=item B<-D vddk.extents=1>

Debug extents returned by C<QueryAllocatedBlocks>.

=item B<-D vddk.datapath=0>

Suppress debugging of datapath calls (C<Read>, C<ReadAsync>, C<Write>
and C<WriteAsync>).

=item B<-D vddk.stats=1>

When the plugin exits print some statistics about each VDDK call.

=back

=head1 FILES

=over 4

=item F<$plugindir/nbdkit-vddk-plugin.so>

The plugin.

Use C<nbdkit --dump-config> to find the location of C<$plugindir>.

=back

=head1 VERSION

C<nbdkit-vddk-plugin> first appeared in nbdkit 1.2.

=head1 SEE ALSO

L<nbdkit(1)>,
L<nbdkit-plugin(3)>,
L<nbdkit-blocksize-filter(1)>,
L<nbdkit-noextents-filter(1)>,
L<nbdkit-readahead-filter(1)>,
L<nbdkit-retry-filter(1)>,
L<nbdkit-scan-filter(1)>,
L<nbdcopy(1)>,
L<nbdinfo(1)>,
L<virsh(1)>,
L<https://gitlab.com/nbdkit/vddk-remote>,
L<https://libvirt.org/drvesx.html>,
L<https://www.vmware.com/support/developer/vddk/>,
VMware document “Best Practices for NBD Transport”.

=head1 AUTHORS

Richard W.M. Jones

=head1 COPYRIGHT

Copyright Red Hat
