nbdkit-vddk-plugin - Man Page

nbdkit VMware VDDK plugin

Synopsis

 nbdkit vddk [file=]FILENAME
             [compression=none|zlib|fastlz|skipz]
             [config=FILENAME] [cookie=COOKIE] [libdir=LIBRARY]
             [nfchostport=PORT] [single-link=true]
             [password=PASSWORD | password=- | password=+FILENAME |
              password=-FD]
             [port=PORT] [server=HOSTNAME] [snapshot=MOREF]
             [thumbprint=THUMBPRINT] [transports=MODE:MODE:...]
             [unbuffered=true] [user=USERNAME] [vm=moref=ID]
 nbdkit vddk --dump-plugin

Description

nbdkit-vddk-plugin is an 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 “Library Location” below).

Examples

Open a local VMDK file

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

When opening local files the filename must be an absolute path.

Because VDDK needs to lock the file, the file must be on a writable filesystem. You can avoid this by opening the file read-only (the -r option):

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

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"

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

server is the hostname of the ESXi server.

thumbprint is the thumb print for validating the SSL certificate. How to find the thumb print of a server is described in “Thumbprints” below.

vm is the Managed Object Reference (“moref”) of the virtual machine. See “Managed Object Reference” below.

The file parameter is the file you want to open, usually in the form "[datastore] vmname/vmname.vmdk". See “File Parameter” below.

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"

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

server is the hostname of the vCenter server.

thumbprint is the thumb print for validating the SSL certificate. How to find the thumb print of a server is described in “Thumbprints” below.

vm is the Managed Object Reference (“moref”) of the virtual machine. See “Managed Object Reference” below.

The file parameter is the file you want to open, usually in the form "[datastore] vmname/vmname.vmdk". See “File Parameter” below.

Parameters

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

For opening a remote connection, file, server, thumbprint, user, password and vm are required.

All other parameters are optional.

compression=none

compression=zlib

compression=fastlz

compression=skipz

(nbdkit ≥ 1.24, vSphere ≥ 6.5)

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

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 /etc/vmware/config and $HOME/.vmware/config. Using config overrides these defaults.

cookie=COOKIE

(vSphere ≥ 6.7)

Cookie from existing authenticated session on the host.

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

[file=]FILENAME

[file=][datastore] vmname/vmname.vmdk

Set the name of the VMDK file to serve.

For local files you must supply an absolute path. For remote files see “File Parameter” section below.

If a VM has multiple disks, nbdkit can only serve one at a time. To serve more than one you must run multiple copies of nbdkit. (See “Notes” below).

file= is a magic config key and may be omitted in most cases. See “Magic parameters” in nbdkit(1).

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 “Library Location” below.

nfchostport=PORT

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

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.

password=-

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

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.

password=-FD

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

port=PORT

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

server=HOSTNAME

The hostname or IP address of VCenter or ESXi host.

single-link=true

(nbdkit ≥ 1.12)

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

snapshot=MOREF

The Managed Object Reference of the snapshot. See “Managed Object Reference” below.

thumbprint=THUMBPRINT

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

The format is 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 “Thumbprints” below for how to get this.

transports=MODE:MODE:...

List of one or more transport modes to use. Possible values include ‘nbd’, ‘nbdssl’, ‘san’, ‘hotadd’, ‘file’ (there may be others). If not given, VDDK will try to choose the best transport mode.

unbuffered=true

(nbdkit ≥ 1.12)

Disable host caching. This corresponds to the VIXDISKLIB_FLAG_OPEN_UNBUFFERED flag.

user=USERNAME

The username to connect to the remote server as.

vm=moref=ID

The Managed Object Reference (“moref”) of the virtual machine. See “Managed Object Reference” below.

vimapiver=APIVER

This parameter is ignored for backwards compatibility.

Library Location

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

You have two choices:

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

But the best advice is to unpack the VDDK tarball anywhere you like and set the libdir=/path/to/vmware-vix-disklib-distrib. For example:
```
 nbdkit vddk \
        libdir=/opt/vmware-vix-disklib-distrib \
        /path/to/file.vmdk
```

No need to set LD_LIBRARY_PATH

In nbdkit ≤ 1.16 you had to set the environment variable LD_LIBRARY_PATH when using this plugin. In nbdkit ≥ 1.18 this is not recommended.

File Parameter

The 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 "[datastore] vmname/vmname.vmdk".

Finding the remote filename

For remote files you can find the path using 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 vpx://:

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

Optional file= prefix

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

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

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.

Using a web browser

Visit 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 thumbprint= parameter.

Using openssl remotely

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

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

By logging in to the ESXi or vCenter server

 # 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

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 -U - -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.

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

If you have libvirt ≥ 3.7, the moref is available in the virsh(1) 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 moRefFinder.pl script written by William Lam (http://www.virtuallyghetto.com/2011/11/vsphere-moref-managed-object-reference.html https://blogs.vmware.com/vsphere/2012/02/uniquely-identifying-virtual-machines-in-vsphere-and-vcloud-part-2-technical.html).

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 “Library Location” above).

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

If it works the output will include:

vddk_default_libdir=...: The compiled-in library path. Use libdir=PATHNAME to override this at runtime.
vddk_has_nfchostport=1: If this is printed then the nfchostport=PORT parameter is supported by this build.
vddk_library_version=...: The VDDK major library version: 6, 7, ... If this is omitted it means the library could not be loaded.
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.
VixDiskLib_...=1: For each VDDK API that the plugin uses and which is present in the VDDK library that was loaded, we print the name of the API (eg. VixDiskLib_Open=1). This lets you see which optional APIs are available, such as VixDiskLib_Flush and VixDiskLib_QueryAllocatedBlocks. If the library could not be loaded then these lines are not printed.

Notes

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 nbdkit-blocksize-filter(1) with the setting minblock=512.

Threads

Handling threads in the VDDK API is complex and does not map well to any of the thread models offered by nbdkit (see “THREADS” in nbdkit-plugin(3)). The plugin uses the nbdkit SERIALIZE_REQUESTS model, but technically even this is not completely safe. This is a subject of future work.

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.

These can be caused by resource limits set on the VMware server. You can increase the limit for the NFC service by editing /etc/vmware/hostd/config.xml and adjusting the <maxMemory> setting:

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

and restarting the hostd service:

 # /etc/init.d/hostd restart

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

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

-v enables verbose messages and the two datapath options disable the very verbose per-read/-write messages. -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: https://gitlab.com/nbdkit/nbdkit/-/commit/5c80f0d290db45a679d55baf37ff39bacb8ce7ec

You can interpret the stats as follows:

Read: The cumulative time spent waiting for VDDK to return from 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.
Write
Flush: Same as above, but for writing and flushing writes.
ReadAsync
WriteAsync: Same as above, but for asynchronous read and write calls introduced in nbdkit 1.30. Unfortunately at the moment the amount of time spent in these calls is not accounted for correctly.
QueryAllocatedBlocks: This call is used to query information about the sparseness of the remote disk. It is only available in VDDK ≥ 6.7. The call is notably very slow in all versions of VMware we have tested.
Open
Close
ConnectEx
Disconnect
InitEx
Exit: The cumulative time spent connecting and disconnecting from the VMware server, which can also be very slow.

Supported Versions of VDDK

This plugin requires VDDK ≥ 6.5 (released Nov 2016). It is only supported on the x64-64 archtecture.

It has been tested with all versions up to 7.0.3 (but should work with future versions).

VDDK 6.7 was the first version that supported the VixDiskLib_QueryAllocatedBlocks API, required to provide extent information over NBD.

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:

-D vddk.diskinfo=1: Debug disk information returned by GetInfo.
-D vddk.extents=1: Debug extents returned by QueryAllocatedBlocks.
-D vddk.datapath=0: Suppress debugging of datapath calls (Read, ReadAsync, Write and WriteAsync).
-D vddk.stats=1: When the plugin exits print some statistics about each VDDK call.

Files

$plugindir/nbdkit-vddk-plugin.so

The plugin.

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

Version

nbdkit-vddk-plugin first appeared in nbdkit 1.2.

Authors

Richard W.M. Jones

Copyright

License

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
Neither the name of Red Hat nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.