mirror of
https://github.com/qemu/qemu.git
synced 2024-12-05 17:53:36 +08:00
bccb135e54
This removes the "only" directives, and lets us use the conventional "DESCRIPTION" section in the manpage. This temporarily drops the qemu-block-drivers documentation from the system manual, but it will be put back (in the right place in the toctree) in a later commit. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Message-id: 20200228153619.9906-14-peter.maydell@linaro.org Message-id: 20200226113034.6741-14-pbonzini@redhat.com Reviewed-by: Peter Maydell <peter.maydell@linaro.org> [PMM: Added commit message note about temporarily losing qemu-block-drivers from the system manual] Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
955 lines
32 KiB
PHP
955 lines
32 KiB
PHP
Disk image file formats
|
|
~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
QEMU supports many image file formats that can be used with VMs as well as with
|
|
any of the tools (like ``qemu-img``). This includes the preferred formats
|
|
raw and qcow2 as well as formats that are supported for compatibility with
|
|
older QEMU versions or other hypervisors.
|
|
|
|
Depending on the image format, different options can be passed to
|
|
``qemu-img create`` and ``qemu-img convert`` using the ``-o`` option.
|
|
This section describes each format and the options that are supported for it.
|
|
|
|
.. program:: image-formats
|
|
.. option:: raw
|
|
|
|
Raw disk image format. This format has the advantage of
|
|
being simple and easily exportable to all other emulators. If your
|
|
file system supports *holes* (for example in ext2 or ext3 on
|
|
Linux or NTFS on Windows), then only the written sectors will reserve
|
|
space. Use ``qemu-img info`` to know the real size used by the
|
|
image or ``ls -ls`` on Unix/Linux.
|
|
|
|
Supported options:
|
|
|
|
.. program:: raw
|
|
.. option:: preallocation
|
|
|
|
Preallocation mode (allowed values: ``off``, ``falloc``,
|
|
``full``). ``falloc`` mode preallocates space for image by
|
|
calling ``posix_fallocate()``. ``full`` mode preallocates space
|
|
for image by writing data to underlying storage. This data may or
|
|
may not be zero, depending on the storage location.
|
|
|
|
.. program:: image-formats
|
|
.. option:: qcow2
|
|
|
|
QEMU image format, the most versatile format. Use it to have smaller
|
|
images (useful if your filesystem does not supports holes, for example
|
|
on Windows), zlib based compression and support of multiple VM
|
|
snapshots.
|
|
|
|
Supported options:
|
|
|
|
.. program:: qcow2
|
|
.. option:: compat
|
|
|
|
Determines the qcow2 version to use. ``compat=0.10`` uses the
|
|
traditional image format that can be read by any QEMU since 0.10.
|
|
``compat=1.1`` enables image format extensions that only QEMU 1.1 and
|
|
newer understand (this is the default). Amongst others, this includes
|
|
zero clusters, which allow efficient copy-on-read for sparse images.
|
|
|
|
.. option:: backing_file
|
|
|
|
File name of a base image (see ``create`` subcommand)
|
|
|
|
.. option:: backing_fmt
|
|
|
|
Image format of the base image
|
|
|
|
.. option:: encryption
|
|
|
|
This option is deprecated and equivalent to ``encrypt.format=aes``
|
|
|
|
.. option:: encrypt.format
|
|
|
|
If this is set to ``luks``, it requests that the qcow2 payload (not
|
|
qcow2 header) be encrypted using the LUKS format. The passphrase to
|
|
use to unlock the LUKS key slot is given by the ``encrypt.key-secret``
|
|
parameter. LUKS encryption parameters can be tuned with the other
|
|
``encrypt.*`` parameters.
|
|
|
|
If this is set to ``aes``, the image is encrypted with 128-bit AES-CBC.
|
|
The encryption key is given by the ``encrypt.key-secret`` parameter.
|
|
This encryption format is considered to be flawed by modern cryptography
|
|
standards, suffering from a number of design problems:
|
|
|
|
- The AES-CBC cipher is used with predictable initialization vectors based
|
|
on the sector number. This makes it vulnerable to chosen plaintext attacks
|
|
which can reveal the existence of encrypted data.
|
|
- The user passphrase is directly used as the encryption key. A poorly
|
|
chosen or short passphrase will compromise the security of the encryption.
|
|
- In the event of the passphrase being compromised there is no way to
|
|
change the passphrase to protect data in any qcow images. The files must
|
|
be cloned, using a different encryption passphrase in the new file. The
|
|
original file must then be securely erased using a program like shred,
|
|
though even this is ineffective with many modern storage technologies.
|
|
|
|
The use of this is no longer supported in system emulators. Support only
|
|
remains in the command line utilities, for the purposes of data liberation
|
|
and interoperability with old versions of QEMU. The ``luks`` format
|
|
should be used instead.
|
|
|
|
.. option:: encrypt.key-secret
|
|
|
|
Provides the ID of a ``secret`` object that contains the passphrase
|
|
(``encrypt.format=luks``) or encryption key (``encrypt.format=aes``).
|
|
|
|
.. option:: encrypt.cipher-alg
|
|
|
|
Name of the cipher algorithm and key length. Currently defaults
|
|
to ``aes-256``. Only used when ``encrypt.format=luks``.
|
|
|
|
.. option:: encrypt.cipher-mode
|
|
|
|
Name of the encryption mode to use. Currently defaults to ``xts``.
|
|
Only used when ``encrypt.format=luks``.
|
|
|
|
.. option:: encrypt.ivgen-alg
|
|
|
|
Name of the initialization vector generator algorithm. Currently defaults
|
|
to ``plain64``. Only used when ``encrypt.format=luks``.
|
|
|
|
.. option:: encrypt.ivgen-hash-alg
|
|
|
|
Name of the hash algorithm to use with the initialization vector generator
|
|
(if required). Defaults to ``sha256``. Only used when ``encrypt.format=luks``.
|
|
|
|
.. option:: encrypt.hash-alg
|
|
|
|
Name of the hash algorithm to use for PBKDF algorithm
|
|
Defaults to ``sha256``. Only used when ``encrypt.format=luks``.
|
|
|
|
.. option:: encrypt.iter-time
|
|
|
|
Amount of time, in milliseconds, to use for PBKDF algorithm per key slot.
|
|
Defaults to ``2000``. Only used when ``encrypt.format=luks``.
|
|
|
|
.. option:: cluster_size
|
|
|
|
Changes the qcow2 cluster size (must be between 512 and 2M). Smaller cluster
|
|
sizes can improve the image file size whereas larger cluster sizes generally
|
|
provide better performance.
|
|
|
|
.. option:: preallocation
|
|
|
|
Preallocation mode (allowed values: ``off``, ``metadata``, ``falloc``,
|
|
``full``). An image with preallocated metadata is initially larger but can
|
|
improve performance when the image needs to grow. ``falloc`` and ``full``
|
|
preallocations are like the same options of ``raw`` format, but sets up
|
|
metadata also.
|
|
|
|
.. option:: lazy_refcounts
|
|
|
|
If this option is set to ``on``, reference count updates are postponed with
|
|
the goal of avoiding metadata I/O and improving performance. This is
|
|
particularly interesting with :option:`cache=writethrough` which doesn't batch
|
|
metadata updates. The tradeoff is that after a host crash, the reference count
|
|
tables must be rebuilt, i.e. on the next open an (automatic) ``qemu-img
|
|
check -r all`` is required, which may take some time.
|
|
|
|
This option can only be enabled if ``compat=1.1`` is specified.
|
|
|
|
.. option:: nocow
|
|
|
|
If this option is set to ``on``, it will turn off COW of the file. It's only
|
|
valid on btrfs, no effect on other file systems.
|
|
|
|
Btrfs has low performance when hosting a VM image file, even more
|
|
when the guest on the VM also using btrfs as file system. Turning off
|
|
COW is a way to mitigate this bad performance. Generally there are two
|
|
ways to turn off COW on btrfs:
|
|
|
|
- Disable it by mounting with nodatacow, then all newly created files
|
|
will be NOCOW.
|
|
- For an empty file, add the NOCOW file attribute. That's what this
|
|
option does.
|
|
|
|
Note: this option is only valid to new or empty files. If there is
|
|
an existing file which is COW and has data blocks already, it couldn't
|
|
be changed to NOCOW by setting ``nocow=on``. One can issue ``lsattr
|
|
filename`` to check if the NOCOW flag is set or not (Capital 'C' is
|
|
NOCOW flag).
|
|
|
|
.. program:: image-formats
|
|
.. option:: qed
|
|
|
|
Old QEMU image format with support for backing files and compact image files
|
|
(when your filesystem or transport medium does not support holes).
|
|
|
|
When converting QED images to qcow2, you might want to consider using the
|
|
``lazy_refcounts=on`` option to get a more QED-like behaviour.
|
|
|
|
Supported options:
|
|
|
|
.. program:: qed
|
|
.. option:: backing_file
|
|
|
|
File name of a base image (see ``create`` subcommand).
|
|
|
|
.. option:: backing_fmt
|
|
|
|
Image file format of backing file (optional). Useful if the format cannot be
|
|
autodetected because it has no header, like some vhd/vpc files.
|
|
|
|
.. option:: cluster_size
|
|
|
|
Changes the cluster size (must be power-of-2 between 4K and 64K). Smaller
|
|
cluster sizes can improve the image file size whereas larger cluster sizes
|
|
generally provide better performance.
|
|
|
|
.. option:: table_size
|
|
|
|
Changes the number of clusters per L1/L2 table (must be
|
|
power-of-2 between 1 and 16). There is normally no need to
|
|
change this value but this option can between used for
|
|
performance benchmarking.
|
|
|
|
.. program:: image-formats
|
|
.. option:: qcow
|
|
|
|
Old QEMU image format with support for backing files, compact image files,
|
|
encryption and compression.
|
|
|
|
Supported options:
|
|
|
|
.. program:: qcow
|
|
.. option:: backing_file
|
|
|
|
File name of a base image (see ``create`` subcommand)
|
|
|
|
.. option:: encryption
|
|
|
|
This option is deprecated and equivalent to ``encrypt.format=aes``
|
|
|
|
.. option:: encrypt.format
|
|
|
|
If this is set to ``aes``, the image is encrypted with 128-bit AES-CBC.
|
|
The encryption key is given by the ``encrypt.key-secret`` parameter.
|
|
This encryption format is considered to be flawed by modern cryptography
|
|
standards, suffering from a number of design problems enumerated previously
|
|
against the ``qcow2`` image format.
|
|
|
|
The use of this is no longer supported in system emulators. Support only
|
|
remains in the command line utilities, for the purposes of data liberation
|
|
and interoperability with old versions of QEMU.
|
|
|
|
Users requiring native encryption should use the ``qcow2`` format
|
|
instead with ``encrypt.format=luks``.
|
|
|
|
.. option:: encrypt.key-secret
|
|
|
|
Provides the ID of a ``secret`` object that contains the encryption
|
|
key (``encrypt.format=aes``).
|
|
|
|
.. program:: image-formats
|
|
.. option:: luks
|
|
|
|
LUKS v1 encryption format, compatible with Linux dm-crypt/cryptsetup
|
|
|
|
Supported options:
|
|
|
|
.. program:: luks
|
|
.. option:: key-secret
|
|
|
|
Provides the ID of a ``secret`` object that contains the passphrase.
|
|
|
|
.. option:: cipher-alg
|
|
|
|
Name of the cipher algorithm and key length. Currently defaults
|
|
to ``aes-256``.
|
|
|
|
.. option:: cipher-mode
|
|
|
|
Name of the encryption mode to use. Currently defaults to ``xts``.
|
|
|
|
.. option:: ivgen-alg
|
|
|
|
Name of the initialization vector generator algorithm. Currently defaults
|
|
to ``plain64``.
|
|
|
|
.. option:: ivgen-hash-alg
|
|
|
|
Name of the hash algorithm to use with the initialization vector generator
|
|
(if required). Defaults to ``sha256``.
|
|
|
|
.. option:: hash-alg
|
|
|
|
Name of the hash algorithm to use for PBKDF algorithm
|
|
Defaults to ``sha256``.
|
|
|
|
.. option:: iter-time
|
|
|
|
Amount of time, in milliseconds, to use for PBKDF algorithm per key slot.
|
|
Defaults to ``2000``.
|
|
|
|
.. program:: image-formats
|
|
.. option:: vdi
|
|
|
|
VirtualBox 1.1 compatible image format.
|
|
|
|
Supported options:
|
|
|
|
.. program:: vdi
|
|
.. option:: static
|
|
|
|
If this option is set to ``on``, the image is created with metadata
|
|
preallocation.
|
|
|
|
.. program:: image-formats
|
|
.. option:: vmdk
|
|
|
|
VMware 3 and 4 compatible image format.
|
|
|
|
Supported options:
|
|
|
|
.. program: vmdk
|
|
.. option:: backing_file
|
|
|
|
File name of a base image (see ``create`` subcommand).
|
|
|
|
.. option:: compat6
|
|
|
|
Create a VMDK version 6 image (instead of version 4)
|
|
|
|
.. option:: hwversion
|
|
|
|
Specify vmdk virtual hardware version. Compat6 flag cannot be enabled
|
|
if hwversion is specified.
|
|
|
|
.. option:: subformat
|
|
|
|
Specifies which VMDK subformat to use. Valid options are
|
|
``monolithicSparse`` (default),
|
|
``monolithicFlat``,
|
|
``twoGbMaxExtentSparse``,
|
|
``twoGbMaxExtentFlat`` and
|
|
``streamOptimized``.
|
|
|
|
.. program:: image-formats
|
|
.. option:: vpc
|
|
|
|
VirtualPC compatible image format (VHD).
|
|
|
|
Supported options:
|
|
|
|
.. program:: vpc
|
|
.. option:: subformat
|
|
|
|
Specifies which VHD subformat to use. Valid options are
|
|
``dynamic`` (default) and ``fixed``.
|
|
|
|
.. program:: image-formats
|
|
.. option:: VHDX
|
|
|
|
Hyper-V compatible image format (VHDX).
|
|
|
|
Supported options:
|
|
|
|
.. program:: VHDX
|
|
.. option:: subformat
|
|
|
|
Specifies which VHDX subformat to use. Valid options are
|
|
``dynamic`` (default) and ``fixed``.
|
|
|
|
.. option:: block_state_zero
|
|
|
|
Force use of payload blocks of type 'ZERO'. Can be set to ``on`` (default)
|
|
or ``off``. When set to ``off``, new blocks will be created as
|
|
``PAYLOAD_BLOCK_NOT_PRESENT``, which means parsers are free to return
|
|
arbitrary data for those blocks. Do not set to ``off`` when using
|
|
``qemu-img convert`` with ``subformat=dynamic``.
|
|
|
|
.. option:: block_size
|
|
|
|
Block size; min 1 MB, max 256 MB. 0 means auto-calculate based on
|
|
image size.
|
|
|
|
.. option:: log_size
|
|
|
|
Log size; min 1 MB.
|
|
|
|
Read-only formats
|
|
~~~~~~~~~~~~~~~~~
|
|
|
|
More disk image file formats are supported in a read-only mode.
|
|
|
|
.. program:: image-formats
|
|
.. option:: bochs
|
|
|
|
Bochs images of ``growing`` type.
|
|
|
|
.. program:: image-formats
|
|
.. option:: cloop
|
|
|
|
Linux Compressed Loop image, useful only to reuse directly compressed
|
|
CD-ROM images present for example in the Knoppix CD-ROMs.
|
|
|
|
.. program:: image-formats
|
|
.. option:: dmg
|
|
|
|
Apple disk image.
|
|
|
|
.. program:: image-formats
|
|
.. option:: parallels
|
|
|
|
Parallels disk image format.
|
|
|
|
Using host drives
|
|
~~~~~~~~~~~~~~~~~
|
|
|
|
In addition to disk image files, QEMU can directly access host
|
|
devices. We describe here the usage for QEMU version >= 0.8.3.
|
|
|
|
Linux
|
|
^^^^^
|
|
|
|
On Linux, you can directly use the host device filename instead of a
|
|
disk image filename provided you have enough privileges to access
|
|
it. For example, use ``/dev/cdrom`` to access to the CDROM.
|
|
|
|
CD
|
|
You can specify a CDROM device even if no CDROM is loaded. QEMU has
|
|
specific code to detect CDROM insertion or removal. CDROM ejection by
|
|
the guest OS is supported. Currently only data CDs are supported.
|
|
|
|
Floppy
|
|
You can specify a floppy device even if no floppy is loaded. Floppy
|
|
removal is currently not detected accurately (if you change floppy
|
|
without doing floppy access while the floppy is not loaded, the guest
|
|
OS will think that the same floppy is loaded).
|
|
Use of the host's floppy device is deprecated, and support for it will
|
|
be removed in a future release.
|
|
|
|
Hard disks
|
|
Hard disks can be used. Normally you must specify the whole disk
|
|
(``/dev/hdb`` instead of ``/dev/hdb1``) so that the guest OS can
|
|
see it as a partitioned disk. WARNING: unless you know what you do, it
|
|
is better to only make READ-ONLY accesses to the hard disk otherwise
|
|
you may corrupt your host data (use the ``-snapshot`` command
|
|
line option or modify the device permissions accordingly).
|
|
|
|
Windows
|
|
^^^^^^^
|
|
|
|
CD
|
|
The preferred syntax is the drive letter (e.g. ``d:``). The
|
|
alternate syntax ``\\.\d:`` is supported. ``/dev/cdrom`` is
|
|
supported as an alias to the first CDROM drive.
|
|
|
|
Currently there is no specific code to handle removable media, so it
|
|
is better to use the ``change`` or ``eject`` monitor commands to
|
|
change or eject media.
|
|
|
|
Hard disks
|
|
Hard disks can be used with the syntax: ``\\.\PhysicalDriveN``
|
|
where *N* is the drive number (0 is the first hard disk).
|
|
|
|
WARNING: unless you know what you do, it is better to only make
|
|
READ-ONLY accesses to the hard disk otherwise you may corrupt your
|
|
host data (use the ``-snapshot`` command line so that the
|
|
modifications are written in a temporary file).
|
|
|
|
Mac OS X
|
|
^^^^^^^^
|
|
|
|
``/dev/cdrom`` is an alias to the first CDROM.
|
|
|
|
Currently there is no specific code to handle removable media, so it
|
|
is better to use the ``change`` or ``eject`` monitor commands to
|
|
change or eject media.
|
|
|
|
Virtual FAT disk images
|
|
~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
QEMU can automatically create a virtual FAT disk image from a
|
|
directory tree. In order to use it, just type:
|
|
|
|
.. parsed-literal::
|
|
|
|
|qemu_system| linux.img -hdb fat:/my_directory
|
|
|
|
Then you access access to all the files in the ``/my_directory``
|
|
directory without having to copy them in a disk image or to export
|
|
them via SAMBA or NFS. The default access is *read-only*.
|
|
|
|
Floppies can be emulated with the ``:floppy:`` option:
|
|
|
|
.. parsed-literal::
|
|
|
|
|qemu_system| linux.img -fda fat:floppy:/my_directory
|
|
|
|
A read/write support is available for testing (beta stage) with the
|
|
``:rw:`` option:
|
|
|
|
.. parsed-literal::
|
|
|
|
|qemu_system| linux.img -fda fat:floppy:rw:/my_directory
|
|
|
|
What you should *never* do:
|
|
|
|
- use non-ASCII filenames
|
|
- use "-snapshot" together with ":rw:"
|
|
- expect it to work when loadvm'ing
|
|
- write to the FAT directory on the host system while accessing it with the guest system
|
|
|
|
NBD access
|
|
~~~~~~~~~~
|
|
|
|
QEMU can access directly to block device exported using the Network Block Device
|
|
protocol.
|
|
|
|
.. parsed-literal::
|
|
|
|
|qemu_system| linux.img -hdb nbd://my_nbd_server.mydomain.org:1024/
|
|
|
|
If the NBD server is located on the same host, you can use an unix socket instead
|
|
of an inet socket:
|
|
|
|
.. parsed-literal::
|
|
|
|
|qemu_system| linux.img -hdb nbd+unix://?socket=/tmp/my_socket
|
|
|
|
In this case, the block device must be exported using qemu-nbd:
|
|
|
|
.. parsed-literal::
|
|
|
|
qemu-nbd --socket=/tmp/my_socket my_disk.qcow2
|
|
|
|
The use of qemu-nbd allows sharing of a disk between several guests:
|
|
|
|
.. parsed-literal::
|
|
|
|
qemu-nbd --socket=/tmp/my_socket --share=2 my_disk.qcow2
|
|
|
|
and then you can use it with two guests:
|
|
|
|
.. parsed-literal::
|
|
|
|
|qemu_system| linux1.img -hdb nbd+unix://?socket=/tmp/my_socket
|
|
|qemu_system| linux2.img -hdb nbd+unix://?socket=/tmp/my_socket
|
|
|
|
If the nbd-server uses named exports (supported since NBD 2.9.18, or with QEMU's
|
|
own embedded NBD server), you must specify an export name in the URI:
|
|
|
|
.. parsed-literal::
|
|
|
|
|qemu_system| -cdrom nbd://localhost/debian-500-ppc-netinst
|
|
|qemu_system| -cdrom nbd://localhost/openSUSE-11.1-ppc-netinst
|
|
|
|
The URI syntax for NBD is supported since QEMU 1.3. An alternative syntax is
|
|
also available. Here are some example of the older syntax:
|
|
|
|
.. parsed-literal::
|
|
|
|
|qemu_system| linux.img -hdb nbd:my_nbd_server.mydomain.org:1024
|
|
|qemu_system| linux2.img -hdb nbd:unix:/tmp/my_socket
|
|
|qemu_system| -cdrom nbd:localhost:10809:exportname=debian-500-ppc-netinst
|
|
|
|
|
|
|
|
Sheepdog disk images
|
|
~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Sheepdog is a distributed storage system for QEMU. It provides highly
|
|
available block level storage volumes that can be attached to
|
|
QEMU-based virtual machines.
|
|
|
|
You can create a Sheepdog disk image with the command:
|
|
|
|
.. parsed-literal::
|
|
|
|
qemu-img create sheepdog:///IMAGE SIZE
|
|
|
|
where *IMAGE* is the Sheepdog image name and *SIZE* is its
|
|
size.
|
|
|
|
To import the existing *FILENAME* to Sheepdog, you can use a
|
|
convert command.
|
|
|
|
.. parsed-literal::
|
|
|
|
qemu-img convert FILENAME sheepdog:///IMAGE
|
|
|
|
You can boot from the Sheepdog disk image with the command:
|
|
|
|
.. parsed-literal::
|
|
|
|
|qemu_system| sheepdog:///IMAGE
|
|
|
|
You can also create a snapshot of the Sheepdog image like qcow2.
|
|
|
|
.. parsed-literal::
|
|
|
|
qemu-img snapshot -c TAG sheepdog:///IMAGE
|
|
|
|
where *TAG* is a tag name of the newly created snapshot.
|
|
|
|
To boot from the Sheepdog snapshot, specify the tag name of the
|
|
snapshot.
|
|
|
|
.. parsed-literal::
|
|
|
|
|qemu_system| sheepdog:///IMAGE#TAG
|
|
|
|
You can create a cloned image from the existing snapshot.
|
|
|
|
.. parsed-literal::
|
|
|
|
qemu-img create -b sheepdog:///BASE#TAG sheepdog:///IMAGE
|
|
|
|
where *BASE* is an image name of the source snapshot and *TAG*
|
|
is its tag name.
|
|
|
|
You can use an unix socket instead of an inet socket:
|
|
|
|
.. parsed-literal::
|
|
|
|
|qemu_system| sheepdog+unix:///IMAGE?socket=PATH
|
|
|
|
If the Sheepdog daemon doesn't run on the local host, you need to
|
|
specify one of the Sheepdog servers to connect to.
|
|
|
|
.. parsed-literal::
|
|
|
|
qemu-img create sheepdog://HOSTNAME:PORT/IMAGE SIZE
|
|
|qemu_system| sheepdog://HOSTNAME:PORT/IMAGE
|
|
|
|
iSCSI LUNs
|
|
~~~~~~~~~~
|
|
|
|
iSCSI is a popular protocol used to access SCSI devices across a computer
|
|
network.
|
|
|
|
There are two different ways iSCSI devices can be used by QEMU.
|
|
|
|
The first method is to mount the iSCSI LUN on the host, and make it appear as
|
|
any other ordinary SCSI device on the host and then to access this device as a
|
|
/dev/sd device from QEMU. How to do this differs between host OSes.
|
|
|
|
The second method involves using the iSCSI initiator that is built into
|
|
QEMU. This provides a mechanism that works the same way regardless of which
|
|
host OS you are running QEMU on. This section will describe this second method
|
|
of using iSCSI together with QEMU.
|
|
|
|
In QEMU, iSCSI devices are described using special iSCSI URLs. URL syntax:
|
|
|
|
::
|
|
|
|
iscsi://[<username>[%<password>]@]<host>[:<port>]/<target-iqn-name>/<lun>
|
|
|
|
Username and password are optional and only used if your target is set up
|
|
using CHAP authentication for access control.
|
|
Alternatively the username and password can also be set via environment
|
|
variables to have these not show up in the process list:
|
|
|
|
::
|
|
|
|
export LIBISCSI_CHAP_USERNAME=<username>
|
|
export LIBISCSI_CHAP_PASSWORD=<password>
|
|
iscsi://<host>/<target-iqn-name>/<lun>
|
|
|
|
Various session related parameters can be set via special options, either
|
|
in a configuration file provided via '-readconfig' or directly on the
|
|
command line.
|
|
|
|
If the initiator-name is not specified qemu will use a default name
|
|
of 'iqn.2008-11.org.linux-kvm[:<uuid>'] where <uuid> is the UUID of the
|
|
virtual machine. If the UUID is not specified qemu will use
|
|
'iqn.2008-11.org.linux-kvm[:<name>'] where <name> is the name of the
|
|
virtual machine.
|
|
|
|
Setting a specific initiator name to use when logging in to the target:
|
|
|
|
::
|
|
|
|
-iscsi initiator-name=iqn.qemu.test:my-initiator
|
|
|
|
Controlling which type of header digest to negotiate with the target:
|
|
|
|
::
|
|
|
|
-iscsi header-digest=CRC32C|CRC32C-NONE|NONE-CRC32C|NONE
|
|
|
|
These can also be set via a configuration file:
|
|
|
|
::
|
|
|
|
[iscsi]
|
|
user = "CHAP username"
|
|
password = "CHAP password"
|
|
initiator-name = "iqn.qemu.test:my-initiator"
|
|
# header digest is one of CRC32C|CRC32C-NONE|NONE-CRC32C|NONE
|
|
header-digest = "CRC32C"
|
|
|
|
Setting the target name allows different options for different targets:
|
|
|
|
::
|
|
|
|
[iscsi "iqn.target.name"]
|
|
user = "CHAP username"
|
|
password = "CHAP password"
|
|
initiator-name = "iqn.qemu.test:my-initiator"
|
|
# header digest is one of CRC32C|CRC32C-NONE|NONE-CRC32C|NONE
|
|
header-digest = "CRC32C"
|
|
|
|
How to use a configuration file to set iSCSI configuration options:
|
|
|
|
.. parsed-literal::
|
|
|
|
cat >iscsi.conf <<EOF
|
|
[iscsi]
|
|
user = "me"
|
|
password = "my password"
|
|
initiator-name = "iqn.qemu.test:my-initiator"
|
|
header-digest = "CRC32C"
|
|
EOF
|
|
|
|
|qemu_system| -drive file=iscsi://127.0.0.1/iqn.qemu.test/1 \\
|
|
-readconfig iscsi.conf
|
|
|
|
How to set up a simple iSCSI target on loopback and access it via QEMU:
|
|
this example shows how to set up an iSCSI target with one CDROM and one DISK
|
|
using the Linux STGT software target. This target is available on Red Hat based
|
|
systems as the package 'scsi-target-utils'.
|
|
|
|
.. parsed-literal::
|
|
|
|
tgtd --iscsi portal=127.0.0.1:3260
|
|
tgtadm --lld iscsi --op new --mode target --tid 1 -T iqn.qemu.test
|
|
tgtadm --lld iscsi --mode logicalunit --op new --tid 1 --lun 1 \\
|
|
-b /IMAGES/disk.img --device-type=disk
|
|
tgtadm --lld iscsi --mode logicalunit --op new --tid 1 --lun 2 \\
|
|
-b /IMAGES/cd.iso --device-type=cd
|
|
tgtadm --lld iscsi --op bind --mode target --tid 1 -I ALL
|
|
|
|
|qemu_system| -iscsi initiator-name=iqn.qemu.test:my-initiator \\
|
|
-boot d -drive file=iscsi://127.0.0.1/iqn.qemu.test/1 \\
|
|
-cdrom iscsi://127.0.0.1/iqn.qemu.test/2
|
|
|
|
GlusterFS disk images
|
|
~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
GlusterFS is a user space distributed file system.
|
|
|
|
You can boot from the GlusterFS disk image with the command:
|
|
|
|
URI:
|
|
|
|
.. parsed-literal::
|
|
|
|
|qemu_system| -drive file=gluster[+TYPE]://[HOST}[:PORT]]/VOLUME/PATH
|
|
[?socket=...][,file.debug=9][,file.logfile=...]
|
|
|
|
JSON:
|
|
|
|
.. parsed-literal::
|
|
|
|
|qemu_system| 'json:{"driver":"qcow2",
|
|
"file":{"driver":"gluster",
|
|
"volume":"testvol","path":"a.img","debug":9,"logfile":"...",
|
|
"server":[{"type":"tcp","host":"...","port":"..."},
|
|
{"type":"unix","socket":"..."}]}}'
|
|
|
|
*gluster* is the protocol.
|
|
|
|
*TYPE* specifies the transport type used to connect to gluster
|
|
management daemon (glusterd). Valid transport types are
|
|
tcp and unix. In the URI form, if a transport type isn't specified,
|
|
then tcp type is assumed.
|
|
|
|
*HOST* specifies the server where the volume file specification for
|
|
the given volume resides. This can be either a hostname or an ipv4 address.
|
|
If transport type is unix, then *HOST* field should not be specified.
|
|
Instead *socket* field needs to be populated with the path to unix domain
|
|
socket.
|
|
|
|
*PORT* is the port number on which glusterd is listening. This is optional
|
|
and if not specified, it defaults to port 24007. If the transport type is unix,
|
|
then *PORT* should not be specified.
|
|
|
|
*VOLUME* is the name of the gluster volume which contains the disk image.
|
|
|
|
*PATH* is the path to the actual disk image that resides on gluster volume.
|
|
|
|
*debug* is the logging level of the gluster protocol driver. Debug levels
|
|
are 0-9, with 9 being the most verbose, and 0 representing no debugging output.
|
|
The default level is 4. The current logging levels defined in the gluster source
|
|
are 0 - None, 1 - Emergency, 2 - Alert, 3 - Critical, 4 - Error, 5 - Warning,
|
|
6 - Notice, 7 - Info, 8 - Debug, 9 - Trace
|
|
|
|
*logfile* is a commandline option to mention log file path which helps in
|
|
logging to the specified file and also help in persisting the gfapi logs. The
|
|
default is stderr.
|
|
|
|
You can create a GlusterFS disk image with the command:
|
|
|
|
.. parsed-literal::
|
|
|
|
qemu-img create gluster://HOST/VOLUME/PATH SIZE
|
|
|
|
Examples
|
|
|
|
.. parsed-literal::
|
|
|
|
|qemu_system| -drive file=gluster://1.2.3.4/testvol/a.img
|
|
|qemu_system| -drive file=gluster+tcp://1.2.3.4/testvol/a.img
|
|
|qemu_system| -drive file=gluster+tcp://1.2.3.4:24007/testvol/dir/a.img
|
|
|qemu_system| -drive file=gluster+tcp://[1:2:3:4:5:6:7:8]/testvol/dir/a.img
|
|
|qemu_system| -drive file=gluster+tcp://[1:2:3:4:5:6:7:8]:24007/testvol/dir/a.img
|
|
|qemu_system| -drive file=gluster+tcp://server.domain.com:24007/testvol/dir/a.img
|
|
|qemu_system| -drive file=gluster+unix:///testvol/dir/a.img?socket=/tmp/glusterd.socket
|
|
|qemu_system| -drive file=gluster+rdma://1.2.3.4:24007/testvol/a.img
|
|
|qemu_system| -drive file=gluster://1.2.3.4/testvol/a.img,file.debug=9,file.logfile=/var/log/qemu-gluster.log
|
|
|qemu_system| 'json:{"driver":"qcow2",
|
|
"file":{"driver":"gluster",
|
|
"volume":"testvol","path":"a.img",
|
|
"debug":9,"logfile":"/var/log/qemu-gluster.log",
|
|
"server":[{"type":"tcp","host":"1.2.3.4","port":24007},
|
|
{"type":"unix","socket":"/var/run/glusterd.socket"}]}}'
|
|
|qemu_system| -drive driver=qcow2,file.driver=gluster,file.volume=testvol,file.path=/path/a.img,
|
|
file.debug=9,file.logfile=/var/log/qemu-gluster.log,
|
|
file.server.0.type=tcp,file.server.0.host=1.2.3.4,file.server.0.port=24007,
|
|
file.server.1.type=unix,file.server.1.socket=/var/run/glusterd.socket
|
|
|
|
Secure Shell (ssh) disk images
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
You can access disk images located on a remote ssh server
|
|
by using the ssh protocol:
|
|
|
|
.. parsed-literal::
|
|
|
|
|qemu_system| -drive file=ssh://[USER@]SERVER[:PORT]/PATH[?host_key_check=HOST_KEY_CHECK]
|
|
|
|
Alternative syntax using properties:
|
|
|
|
.. parsed-literal::
|
|
|
|
|qemu_system| -drive file.driver=ssh[,file.user=USER],file.host=SERVER[,file.port=PORT],file.path=PATH[,file.host_key_check=HOST_KEY_CHECK]
|
|
|
|
*ssh* is the protocol.
|
|
|
|
*USER* is the remote user. If not specified, then the local
|
|
username is tried.
|
|
|
|
*SERVER* specifies the remote ssh server. Any ssh server can be
|
|
used, but it must implement the sftp-server protocol. Most Unix/Linux
|
|
systems should work without requiring any extra configuration.
|
|
|
|
*PORT* is the port number on which sshd is listening. By default
|
|
the standard ssh port (22) is used.
|
|
|
|
*PATH* is the path to the disk image.
|
|
|
|
The optional *HOST_KEY_CHECK* parameter controls how the remote
|
|
host's key is checked. The default is ``yes`` which means to use
|
|
the local ``.ssh/known_hosts`` file. Setting this to ``no``
|
|
turns off known-hosts checking. Or you can check that the host key
|
|
matches a specific fingerprint:
|
|
``host_key_check=md5:78:45:8e:14:57:4f:d5:45:83:0a:0e:f3:49:82:c9:c8``
|
|
(``sha1:`` can also be used as a prefix, but note that OpenSSH
|
|
tools only use MD5 to print fingerprints).
|
|
|
|
Currently authentication must be done using ssh-agent. Other
|
|
authentication methods may be supported in future.
|
|
|
|
Note: Many ssh servers do not support an ``fsync``-style operation.
|
|
The ssh driver cannot guarantee that disk flush requests are
|
|
obeyed, and this causes a risk of disk corruption if the remote
|
|
server or network goes down during writes. The driver will
|
|
print a warning when ``fsync`` is not supported:
|
|
|
|
::
|
|
|
|
warning: ssh server ssh.example.com:22 does not support fsync
|
|
|
|
With sufficiently new versions of libssh and OpenSSH, ``fsync`` is
|
|
supported.
|
|
|
|
NVMe disk images
|
|
~~~~~~~~~~~~~~~~
|
|
|
|
NVM Express (NVMe) storage controllers can be accessed directly by a userspace
|
|
driver in QEMU. This bypasses the host kernel file system and block layers
|
|
while retaining QEMU block layer functionalities, such as block jobs, I/O
|
|
throttling, image formats, etc. Disk I/O performance is typically higher than
|
|
with ``-drive file=/dev/sda`` using either thread pool or linux-aio.
|
|
|
|
The controller will be exclusively used by the QEMU process once started. To be
|
|
able to share storage between multiple VMs and other applications on the host,
|
|
please use the file based protocols.
|
|
|
|
Before starting QEMU, bind the host NVMe controller to the host vfio-pci
|
|
driver. For example:
|
|
|
|
.. parsed-literal::
|
|
|
|
# modprobe vfio-pci
|
|
# lspci -n -s 0000:06:0d.0
|
|
06:0d.0 0401: 1102:0002 (rev 08)
|
|
# echo 0000:06:0d.0 > /sys/bus/pci/devices/0000:06:0d.0/driver/unbind
|
|
# echo 1102 0002 > /sys/bus/pci/drivers/vfio-pci/new_id
|
|
|
|
# |qemu_system| -drive file=nvme://HOST:BUS:SLOT.FUNC/NAMESPACE
|
|
|
|
Alternative syntax using properties:
|
|
|
|
.. parsed-literal::
|
|
|
|
|qemu_system| -drive file.driver=nvme,file.device=HOST:BUS:SLOT.FUNC,file.namespace=NAMESPACE
|
|
|
|
*HOST*:*BUS*:*SLOT*.\ *FUNC* is the NVMe controller's PCI device
|
|
address on the host.
|
|
|
|
*NAMESPACE* is the NVMe namespace number, starting from 1.
|
|
|
|
Disk image file locking
|
|
~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
By default, QEMU tries to protect image files from unexpected concurrent
|
|
access, as long as it's supported by the block protocol driver and host
|
|
operating system. If multiple QEMU processes (including QEMU emulators and
|
|
utilities) try to open the same image with conflicting accessing modes, all but
|
|
the first one will get an error.
|
|
|
|
This feature is currently supported by the file protocol on Linux with the Open
|
|
File Descriptor (OFD) locking API, and can be configured to fall back to POSIX
|
|
locking if the POSIX host doesn't support Linux OFD locking.
|
|
|
|
To explicitly enable image locking, specify "locking=on" in the file protocol
|
|
driver options. If OFD locking is not possible, a warning will be printed and
|
|
the POSIX locking API will be used. In this case there is a risk that the lock
|
|
will get silently lost when doing hot plugging and block jobs, due to the
|
|
shortcomings of the POSIX locking API.
|
|
|
|
QEMU transparently handles lock handover during shared storage migration. For
|
|
shared virtual disk images between multiple VMs, the "share-rw" device option
|
|
should be used.
|
|
|
|
By default, the guest has exclusive write access to its disk image. If the
|
|
guest can safely share the disk image with other writers the
|
|
``-device ...,share-rw=on`` parameter can be used. This is only safe if
|
|
the guest is running software, such as a cluster file system, that
|
|
coordinates disk accesses to avoid corruption.
|
|
|
|
Note that share-rw=on only declares the guest's ability to share the disk.
|
|
Some QEMU features, such as image file formats, require exclusive write access
|
|
to the disk image and this is unaffected by the share-rw=on option.
|
|
|
|
Alternatively, locking can be fully disabled by "locking=off" block device
|
|
option. In the command line, the option is usually in the form of
|
|
"file.locking=off" as the protocol driver is normally placed as a "file" child
|
|
under a format driver. For example:
|
|
|
|
::
|
|
|
|
-blockdev driver=qcow2,file.filename=/path/to/image,file.locking=off,file.driver=file
|
|
|
|
To check if image locking is active, check the output of the "lslocks" command
|
|
on host and see if there are locks held by the QEMU process on the image file.
|
|
More than one byte could be locked by the QEMU instance, each byte of which
|
|
reflects a particular permission that is acquired or protected by the running
|
|
block driver.
|