openstack/nova-specs
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Update AIO mode spec with recent comments

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There was a valuable discussion in the review which I would like
to include in the approved spec for future reference.

Change-Id: Ifada0c71d9a77f0e34f371d6883e9f0f0b5f5866
Implements: blueprint libvirt-aio-mode
This commit is contained in:
Alexander Schmidt
2015-12-04 15:28:20 +00:00
parent 6e8034a63f
commit 1f8fda72d1
1 changed files with 10 additions and 6 deletions
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16
specs/mitaka/approved/libvirt-aio-mode.rst
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@@ -65,9 +65,10 @@ attachment of the guest disk.
Restrictions on when to use native AIO mode
-------------------------------------------
* native AIO mode is a bad idea if the storage is not fully pre-allocated,
e.g. for qcow2 images that grow on demand or sparse LVM storage (source:
danpb / KVM maintainers)
* Native AIO mode will not be enabled for sparse images as it can cause
Qemu threads to be blocked when filesystem metadata need to be updated.
This issue is much more unlikely to appear when using preallocated
images. For the full discussion, see the IRC log in `[4]`_.
* AIO mode has no effect if using the in-qemu network clients (any disks
that use <disk type='network'>). It is only relevant if using the
in-kernel network drivers (source: danpb)
@@ -182,15 +183,18 @@ should be updated.
References
==========
* General overview on AIO:
* _`[1]` General overview on AIO:
http://www.ibm.com/developerworks/library/l-async/
* Best practices: Asynchronous I/O model for KVM guests
* _`[2]` Best practices: Asynchronous I/O model for KVM guests
https://www-01.ibm.com/support/knowledgecenter/linuxonibm/liaat/liaatbpkvmasynchio.htm
* Libvirt and QEMU Performance Tweaks for KVM Guests
* _`[3]` Libvirt and QEMU Performance Tweaks for KVM Guests
"http://wiki.mikejung.biz/KVM/_Xen#AIO_Modes"
* _`[4]` qemu irc log
http://paste.openstack.org/show/480498/
History
=======