4 In general features are intended to be supported indefinitely once
5 introduced into QEMU. In the event that a feature needs to be removed,
6 it will be listed in this section. The feature will remain functional
7 for 2 releases prior to actual removal. Deprecated features may also
8 generate warnings on the console when QEMU starts up, or if activated
9 via a monitor command, however, this is not a mandatory requirement.
11 Prior to the 2.10.0 release there was no official policy on how
12 long features would be deprecated prior to their removal, nor
13 any documented list of which features were deprecated. Thus
14 any features deprecated prior to 2.10.0 will be treated as if
15 they were first deprecated in the 2.10.0 release.
17 What follows is a list of all features currently marked as
20 System emulator command line arguments
21 --------------------------------------
23 ``-machine enforce-config-section=on|off`` (since 3.1)
24 ''''''''''''''''''''''''''''''''''''''''''''''''''''''
26 The ``enforce-config-section`` parameter is replaced by the
27 ``-global migration.send-configuration={on|off}`` option.
29 ``-no-kvm`` (since 1.3.0)
30 '''''''''''''''''''''''''
32 The ``-no-kvm`` argument is now a synonym for setting ``-accel tcg``.
34 ``-usbdevice`` (since 2.10.0)
35 '''''''''''''''''''''''''''''
37 The ``-usbdevice DEV`` argument is now a synonym for setting
38 the ``-device usb-DEV`` argument instead. The deprecated syntax
39 would automatically enable USB support on the machine type.
40 If using the new syntax, USB support must be explicitly
41 enabled via the ``-machine usb=on`` argument.
43 ``-drive file=json:{...{'driver':'file'}}`` (since 3.0)
44 '''''''''''''''''''''''''''''''''''''''''''''''''''''''
46 The 'file' driver for drives is no longer appropriate for character or host
47 devices and will only accept regular files (S_IFREG). The correct driver
48 for these file types is 'host_cdrom' or 'host_device' as appropriate.
50 ``-smp`` (invalid topologies) (since 3.1)
51 '''''''''''''''''''''''''''''''''''''''''
53 CPU topology properties should describe whole machine topology including
56 However, historically it was possible to start QEMU with an incorrect topology
57 where *n* <= *sockets* * *cores* * *threads* < *maxcpus*,
58 which could lead to an incorrect topology enumeration by the guest.
59 Support for invalid topologies will be removed, the user must ensure
60 topologies described with -smp include all possible cpus, i.e.
61 *sockets* * *cores* * *threads* = *maxcpus*.
63 ``-vnc acl`` (since 4.0.0)
64 ''''''''''''''''''''''''''
66 The ``acl`` option to the ``-vnc`` argument has been replaced
67 by the ``tls-authz`` and ``sasl-authz`` options.
69 ``QEMU_AUDIO_`` environment variables and ``-audio-help`` (since 4.0)
70 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
72 The ``-audiodev`` argument is now the preferred way to specify audio
73 backend settings instead of environment variables. To ease migration to
74 the new format, the ``-audiodev-help`` option can be used to convert
75 the current values of the environment variables to ``-audiodev`` options.
77 Creating sound card devices and vnc without ``audiodev=`` property (since 4.2)
78 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
80 When not using the deprecated legacy audio config, each sound card
81 should specify an ``audiodev=`` property. Additionally, when using
82 vnc, you should specify an ``audiodev=`` propery if you plan to
83 transmit audio through the VNC protocol.
85 Creating sound card devices using ``-soundhw`` (since 5.1)
86 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
88 Sound card devices should be created using ``-device`` instead. The
89 names are the same for most devices. The exceptions are ``hda`` which
90 needs two devices (``-device intel-hda -device hda-duplex``) and
91 ``pcspk`` which can be activated using ``-machine
92 pcspk-audiodev=<name>``.
94 ``-mon ...,control=readline,pretty=on|off`` (since 4.1)
95 '''''''''''''''''''''''''''''''''''''''''''''''''''''''
97 The ``pretty=on|off`` switch has no effect for HMP monitors, but is
98 silently ignored. Using the switch with HMP monitors will become an
101 ``-realtime`` (since 4.1)
102 '''''''''''''''''''''''''
104 The ``-realtime mlock=on|off`` argument has been replaced by the
105 ``-overcommit mem-lock=on|off`` argument.
107 ``-numa`` node (without memory specified) (since 4.1)
108 '''''''''''''''''''''''''''''''''''''''''''''''''''''
110 Splitting RAM by default between NUMA nodes has the same issues as ``mem``
111 parameter described above with the difference that the role of the user plays
112 QEMU using implicit generic or board specific splitting rule.
113 Use ``memdev`` with *memory-backend-ram* backend or ``mem`` (if
114 it's supported by used machine type) to define mapping explictly instead.
116 ``-mem-path`` fallback to RAM (since 4.1)
117 '''''''''''''''''''''''''''''''''''''''''
119 Currently if guest RAM allocation from file pointed by ``mem-path``
120 fails, QEMU falls back to allocating from RAM, which might result
121 in unpredictable behavior since the backing file specified by the user
122 is ignored. In the future, users will be responsible for making sure
123 the backing storage specified with ``-mem-path`` can actually provide
124 the guest RAM configured with ``-m`` and QEMU will fail to start up if
125 RAM allocation is unsuccessful.
127 RISC-V ``-bios`` (since 5.1)
128 ''''''''''''''''''''''''''''
130 QEMU 4.1 introduced support for the -bios option in QEMU for RISC-V for the
131 RISC-V virt machine and sifive_u machine. QEMU 4.1 had no changes to the
132 default behaviour to avoid breakages.
134 QEMU 5.1 changes the default behaviour from ``-bios none`` to ``-bios default``.
136 QEMU 5.1 has three options:
137 1. ``-bios default`` - This is the current default behavior if no -bios option
138 is included. This option will load the default OpenSBI firmware automatically.
139 The firmware is included with the QEMU release and no user interaction is
140 required. All a user needs to do is specify the kernel they want to boot
141 with the -kernel option
142 2. ``-bios none`` - QEMU will not automatically load any firmware. It is up
143 to the user to load all the images they need.
144 3. ``-bios <file>`` - Tells QEMU to load the specified file as the firmwrae.
146 ``-tb-size`` option (since 5.0)
147 '''''''''''''''''''''''''''''''
149 QEMU 5.0 introduced an alternative syntax to specify the size of the translation
150 block cache, ``-accel tcg,tb-size=``. The new syntax deprecates the
151 previously available ``-tb-size`` option.
153 ``-show-cursor`` option (since 5.0)
154 '''''''''''''''''''''''''''''''''''
156 Use ``-display sdl,show-cursor=on`` or
157 ``-display gtk,show-cursor=on`` instead.
159 ``Configuring floppies with ``-global``
160 '''''''''''''''''''''''''''''''''''''''
162 Use ``-device floppy,...`` instead:
165 -global isa-fdc.driveA=...
166 -global sysbus-fdc.driveA=...
167 -global SUNW,fdtwo.drive=...
172 -device floppy,unit=0,drive=...
177 -global isa-fdc.driveB=...
178 -global sysbus-fdc.driveB=...
183 -device floppy,unit=1,drive=...
185 ``-drive`` with bogus interface type
186 ''''''''''''''''''''''''''''''''''''
188 Drives with interface types other than ``if=none`` are for onboard
189 devices. It is possible to use drives the board doesn't pick up with
190 -device. This usage is now deprecated. Use ``if=none`` instead.
193 QEMU Machine Protocol (QMP) commands
194 ------------------------------------
196 ``change`` (since 2.5.0)
197 ''''''''''''''''''''''''
199 Use ``blockdev-change-medium`` or ``change-vnc-password`` instead.
201 ``blockdev-open-tray``, ``blockdev-close-tray`` argument ``device`` (since 2.8.0)
202 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
204 Use argument ``id`` instead.
206 ``eject`` argument ``device`` (since 2.8.0)
207 '''''''''''''''''''''''''''''''''''''''''''
209 Use argument ``id`` instead.
211 ``blockdev-change-medium`` argument ``device`` (since 2.8.0)
212 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
214 Use argument ``id`` instead.
216 ``block_set_io_throttle`` argument ``device`` (since 2.8.0)
217 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
219 Use argument ``id`` instead.
221 ``migrate_set_downtime`` and ``migrate_set_speed`` (since 2.8.0)
222 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
224 Use ``migrate-set-parameters`` instead.
226 ``query-named-block-nodes`` result ``encryption_key_missing`` (since 2.10.0)
227 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
231 ``query-block`` result ``inserted.encryption_key_missing`` (since 2.10.0)
232 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
236 ``blockdev-add`` empty string argument ``backing`` (since 2.10.0)
237 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
239 Use argument value ``null`` instead.
241 ``migrate-set-cache-size`` and ``query-migrate-cache-size`` (since 2.11.0)
242 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
244 Use ``migrate-set-parameters`` and ``query-migrate-parameters`` instead.
246 ``block-commit`` arguments ``base`` and ``top`` (since 3.1.0)
247 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
249 Use arguments ``base-node`` and ``top-node`` instead.
251 ``object-add`` option ``props`` (since 5.0)
252 '''''''''''''''''''''''''''''''''''''''''''
254 Specify the properties for the object as top-level arguments instead.
256 ``query-named-block-nodes`` and ``query-block`` result dirty-bitmaps[i].status (since 4.0)
257 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
259 The ``status`` field of the ``BlockDirtyInfo`` structure, returned by
260 these commands is deprecated. Two new boolean fields, ``recording`` and
261 ``busy`` effectively replace it.
263 ``query-block`` result field ``dirty-bitmaps`` (Since 4.2)
264 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
266 The ``dirty-bitmaps`` field of the ``BlockInfo`` structure, returned by
267 the query-block command is itself now deprecated. The ``dirty-bitmaps``
268 field of the ``BlockDeviceInfo`` struct should be used instead, which is the
269 type of the ``inserted`` field in query-block replies, as well as the
270 type of array items in query-named-block-nodes.
272 Since the ``dirty-bitmaps`` field is optionally present in both the old and
273 new locations, clients must use introspection to learn where to anticipate
274 the field if/when it does appear in command output.
276 ``query-cpus`` (since 2.12.0)
277 '''''''''''''''''''''''''''''
279 The ``query-cpus`` command is replaced by the ``query-cpus-fast`` command.
281 ``query-cpus-fast`` ``arch`` output member (since 3.0.0)
282 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''
284 The ``arch`` output member of the ``query-cpus-fast`` command is
285 replaced by the ``target`` output member.
287 ``cpu-add`` (since 4.0)
288 '''''''''''''''''''''''
290 Use ``device_add`` for hotplugging vCPUs instead of ``cpu-add``. See
291 documentation of ``query-hotpluggable-cpus`` for additional
294 ``query-events`` (since 4.0)
295 ''''''''''''''''''''''''''''
297 The ``query-events`` command has been superseded by the more powerful
298 and accurate ``query-qmp-schema`` command.
300 chardev client socket with ``wait`` option (since 4.0)
301 ''''''''''''''''''''''''''''''''''''''''''''''''''''''
303 Character devices creating sockets in client mode should not specify
304 the 'wait' field, which is only applicable to sockets in server mode
306 Human Monitor Protocol (HMP) commands
307 -------------------------------------
309 ``cpu-add`` (since 4.0)
310 '''''''''''''''''''''''
312 Use ``device_add`` for hotplugging vCPUs instead of ``cpu-add``. See
313 documentation of ``query-hotpluggable-cpus`` for additional details.
315 ``acl_show``, ``acl_reset``, ``acl_policy``, ``acl_add``, ``acl_remove`` (since 4.0.0)
316 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
318 The ``acl_show``, ``acl_reset``, ``acl_policy``, ``acl_add``, and
319 ``acl_remove`` commands are deprecated with no replacement. Authorization
320 for VNC should be performed using the pluggable QAuthZ objects.
325 ``compat`` property of server class POWER CPUs (since 5.0)
326 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
328 The ``compat`` property used to set backwards compatibility modes for
329 the processor has been deprecated. The ``max-cpu-compat`` property of
330 the ``pseries`` machine type should be used instead.
332 System emulator devices
333 -----------------------
335 ``ide-drive`` (since 4.2)
336 '''''''''''''''''''''''''
338 The 'ide-drive' device is deprecated. Users should use 'ide-hd' or
339 'ide-cd' as appropriate to get an IDE hard disk or CD-ROM as needed.
341 ``scsi-disk`` (since 4.2)
342 '''''''''''''''''''''''''
344 The 'scsi-disk' device is deprecated. Users should use 'scsi-hd' or
345 'scsi-cd' as appropriate to get a SCSI hard disk or CD-ROM as needed.
347 System emulator machines
348 ------------------------
350 mips ``r4k`` platform (since 5.0)
351 '''''''''''''''''''''''''''''''''
353 This machine type is very old and unmaintained. Users should use the ``malta``
354 machine type instead.
356 mips ``fulong2e`` machine (since 5.1)
357 '''''''''''''''''''''''''''''''''''''
359 This machine has been renamed ``fuloong2e``.
361 ``pc-1.0``, ``pc-1.1``, ``pc-1.2`` and ``pc-1.3`` (since 5.0)
362 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
364 These machine types are very old and likely can not be used for live migration
365 from old QEMU versions anymore. A newer machine type should be used instead.
370 Emulated device options
371 '''''''''''''''''''''''
373 ``-device virtio-blk,scsi=on|off`` (since 5.0.0)
374 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
376 The virtio-blk SCSI passthrough feature is a legacy VIRTIO feature. VIRTIO 1.0
377 and later do not support it because the virtio-scsi device was introduced for
378 full SCSI support. Use virtio-scsi instead when SCSI passthrough is required.
380 Note this also applies to ``-device virtio-blk-pci,scsi=on|off``, which is an
386 ``"backing": ""`` (since 2.12.0)
387 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
389 In order to prevent QEMU from automatically opening an image's backing
390 chain, use ``"backing": null`` instead.
392 ``rbd`` keyvalue pair encoded filenames: ``""`` (since 3.1.0)
393 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
395 Options for ``rbd`` should be specified according to its runtime options,
396 like other block drivers. Legacy parsing of keyvalue pair encoded
397 filenames is useful to open images with the old format for backing files;
398 These image files should be updated to use the current format.
400 Example of legacy encoding::
402 json:{"file.driver":"rbd", "file.filename":"rbd:rbd/name"}
404 The above, converted to the current supported format::
406 json:{"file.driver":"rbd", "file.pool":"rbd", "file.image":"name"}
411 ``tilegx`` CPUs (since 5.1.0)
412 '''''''''''''''''''''''''''''
414 The ``tilegx`` guest CPU support (which was only implemented in
415 linux-user mode) is deprecated and will be removed in a future version
416 of QEMU. Support for this CPU was removed from the upstream Linux
417 kernel in 2018, and has also been dropped from glibc.
419 ``ppc64abi32`` CPUs (since 5.2.0)
420 '''''''''''''''''''''''''''''''''
422 The ``ppc64abi32`` architecture has a number of issues which regularly
423 trip up our CI testing and is suspected to be quite broken. For that
424 reason the maintainers strongly suspect no one actually uses it.
429 qemu-img amend to adjust backing file (since 5.1)
430 '''''''''''''''''''''''''''''''''''''''''''''''''
432 The use of ``qemu-img amend`` to modify the name or format of a qcow2
433 backing image is deprecated; this functionality was never fully
434 documented or tested, and interferes with other amend operations that
435 need access to the original backing image (such as deciding whether a
436 v3 zero cluster may be left unallocated when converting to a v2
437 image). Rather, any changes to the backing chain should be performed
438 with ``qemu-img rebase -u`` either before or after the remaining
439 changes being performed by amend, as appropriate.
441 qemu-img backing file without format (since 5.1)
442 ''''''''''''''''''''''''''''''''''''''''''''''''
444 The use of ``qemu-img create``, ``qemu-img rebase``, or ``qemu-img
445 convert`` to create or modify an image that depends on a backing file
446 now recommends that an explicit backing format be provided. This is
447 for safety: if QEMU probes a different format than what you thought,
448 the data presented to the guest will be corrupt; similarly, presenting
449 a raw image to a guest allows a potential security exploit if a future
450 probe sees a non-raw image based on guest writes.
452 To avoid the warning message, or even future refusal to create an
453 unsafe image, you must pass ``-o backing_fmt=`` (or the shorthand
454 ``-F`` during create) to specify the intended backing format. You may
455 use ``qemu-img rebase -u`` to retroactively add a backing format to an
456 existing image. However, be aware that there are already potential
457 security risks to blindly using ``qemu-img info`` to probe the format
458 of an untrusted backing image, when deciding what format to add into
461 Backwards compatibility
462 -----------------------
464 Runnability guarantee of CPU models (since 4.1.0)
465 '''''''''''''''''''''''''''''''''''''''''''''''''
467 Previous versions of QEMU never changed existing CPU models in
468 ways that introduced additional host software or hardware
469 requirements to the VM. This allowed management software to
470 safely change the machine type of an existing VM without
471 introducing new requirements ("runnability guarantee"). This
472 prevented CPU models from being updated to include CPU
473 vulnerability mitigations, leaving guests vulnerable in the
474 default configuration.
476 The CPU model runnability guarantee won't apply anymore to
477 existing CPU models. Management software that needs runnability
478 guarantees must resolve the CPU model aliases using te
479 ``alias-of`` field returned by the ``query-cpu-definitions`` QMP
482 While those guarantees are kept, the return value of
483 ``query-cpu-definitions`` will have existing CPU model aliases
484 point to a version that doesn't break runnability guarantees
485 (specifically, version 1 of those CPU models). In future QEMU
486 versions, aliases will point to newer CPU model versions
487 depending on the machine type, so management software must
488 resolve CPU model aliases before starting a virtual machine.
491 Recently removed features
492 =========================
494 What follows is a record of recently removed, formerly deprecated
495 features that serves as a record for users who have encountered
496 trouble after a recent upgrade.
498 System emulator command line arguments
499 --------------------------------------
501 ``-net ...,name=``\ *name* (removed in 5.1)
502 '''''''''''''''''''''''''''''''''''''''''''
504 The ``name`` parameter of the ``-net`` option was a synonym
505 for the ``id`` parameter, which should now be used instead.
507 QEMU Machine Protocol (QMP) commands
508 ------------------------------------
510 ``block-dirty-bitmap-add`` "autoload" parameter (since 4.2.0)
511 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
513 The "autoload" parameter has been ignored since 2.12.0. All bitmaps
514 are automatically loaded from qcow2 images.
516 Human Monitor Protocol (HMP) commands
517 -------------------------------------
519 The ``hub_id`` parameter of ``hostfwd_add`` / ``hostfwd_remove`` (removed in 5.0)
520 '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
522 The ``[hub_id name]`` parameter tuple of the 'hostfwd_add' and
523 'hostfwd_remove' HMP commands has been replaced by ``netdev_id``.
528 RISC-V ISA privledge specification version 1.09.1 (removed in 5.1)
529 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
531 The RISC-V ISA privledge specification version 1.09.1 has been removed.
532 QEMU supports both the newer version 1.10.0 and the ratified version 1.11.0, these
533 should be used instead of the 1.09.1 version.
538 KVM guest support on 32-bit Arm hosts (removed in 5.2)
539 ''''''''''''''''''''''''''''''''''''''''''''''''''''''
541 The Linux kernel has dropped support for allowing 32-bit Arm systems
542 to host KVM guests as of the 5.7 kernel. Accordingly, QEMU is deprecating
543 its support for this configuration and will remove it in a future version.
544 Running 32-bit guests on a 64-bit Arm host remains supported.
546 RISC-V ISA Specific CPUs (removed in 5.1)
547 '''''''''''''''''''''''''''''''''''''''''
549 The RISC-V cpus with the ISA version in the CPU name have been removed. The
550 four CPUs are: ``rv32gcsu-v1.9.1``, ``rv32gcsu-v1.10.0``, ``rv64gcsu-v1.9.1`` and
551 ``rv64gcsu-v1.10.0``. Instead the version can be specified via the CPU ``priv_spec``
552 option when using the ``rv32`` or ``rv64`` CPUs.
554 RISC-V no MMU CPUs (removed in 5.1)
555 '''''''''''''''''''''''''''''''''''
557 The RISC-V no MMU cpus have been removed. The two CPUs: ``rv32imacu-nommu`` and
558 ``rv64imacu-nommu`` can no longer be used. Instead the MMU status can be specified
559 via the CPU ``mmu`` option when using the ``rv32`` or ``rv64`` CPUs.
561 System emulator machines
562 ------------------------
564 ``spike_v1.9.1`` and ``spike_v1.10`` (removed in 5.1)
565 '''''''''''''''''''''''''''''''''''''''''''''''''''''
567 The version specific Spike machines have been removed in favour of the
568 generic ``spike`` machine. If you need to specify an older version of the RISC-V
569 spec you can use the ``-cpu rv64gcsu,priv_spec=v1.10.0`` command line argument.
574 ``qemu-nbd --partition`` (removed in 5.0)
575 '''''''''''''''''''''''''''''''''''''''''
577 The ``qemu-nbd --partition $digit`` code (also spelled ``-P``)
578 could only handle MBR partitions, and never correctly handled logical
579 partitions beyond partition 5. Exporting a partition can still be
580 done by utilizing the ``--image-opts`` option with a raw blockdev
581 using the ``offset`` and ``size`` parameters layered on top of
582 any other existing blockdev. For example, if partition 1 is 100MiB
583 long starting at 1MiB, the old command::
585 qemu-nbd -t -P 1 -f qcow2 file.qcow2
587 can be rewritten as::
589 qemu-nbd -t --image-opts driver=raw,offset=1M,size=100M,file.driver=qcow2,file.file.driver=file,file.file.filename=file.qcow2
591 ``qemu-img convert -n -o`` (removed in 5.1)
592 '''''''''''''''''''''''''''''''''''''''''''
594 All options specified in ``-o`` are image creation options, so
595 they are now rejected when used with ``-n`` to skip image creation.
598 ``qemu-img create -b bad file $size`` (removed in 5.1)
599 ''''''''''''''''''''''''''''''''''''''''''''''''''''''
601 When creating an image with a backing file that could not be opened,
602 ``qemu-img create`` used to issue a warning about the failure but
603 proceed with the image creation if an explicit size was provided.
604 However, as the ``-u`` option exists for this purpose, it is safer to
605 enforce that any failure to open the backing image (including if the
606 backing file is missing or an incorrect format was specified) is an
607 error when ``-u`` is not used.
612 ``-numa node,mem=``\ *size* (removed in 5.1)
613 ''''''''''''''''''''''''''''''''''''''''''''
615 The parameter ``mem`` of ``-numa node`` was used to assign a part of
616 guest RAM to a NUMA node. But when using it, it's impossible to manage a specified
617 RAM chunk on the host side (like bind it to a host node, setting bind policy, ...),
618 so the guest ends up with the fake NUMA configuration with suboptiomal performance.
619 However since 2014 there is an alternative way to assign RAM to a NUMA node
620 using parameter ``memdev``, which does the same as ``mem`` and adds
621 means to actually manage node RAM on the host side. Use parameter ``memdev``
622 with *memory-backend-ram* backend as replacement for parameter ``mem``
623 to achieve the same fake NUMA effect or a properly configured
624 *memory-backend-file* backend to actually benefit from NUMA configuration.
625 New machine versions (since 5.1) will not accept the option but it will still
626 work with old machine types. User can check the QAPI schema to see if the legacy
627 option is supported by looking at MachineInfo::numa-mem-supported property.
632 VXHS backend (removed in 5.1)
633 '''''''''''''''''''''''''''''
635 The VXHS code does not compile since v2.12.0. It was removed in 5.1.