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Public bug reported:
In this thread:
http://lists.openstack.org/pipermail/openstack/2015-August/013614.html
[qote]
Running cmd (subprocess): sudo nova-rootwrap /etc/nova/rootwrap.conf qemu-img convert -O raw /var/lib/nova/instances/_base/999f7fff2521e4a7243c9e1d21599fd64a19b42e /dev/openstack-controller01-ky01-vg/5f831046-435c-4636-8b71-a662327b608c_disk
Well, I understand what this step is doing - it's copying raw image to
lvm.
How can we speed it up?
I don't wanna have instance from 100GB image booted for 4 hours
[/quote]
Regardless of how much data is in the source file, qemu-img has to write
out the full virtual size on the target block dev to ensure any pre-
existing data is overwritten. THis may involve writing 100's of GB of
zeros for large images.
qemu-img does has an optimization to let it use 'discard' as a fast
alternative to writing zeros, but this requires that qemu-img has disk
caching disabled , eg -t none. We should investigate to see if this
improves performance for converting large images to block devices, and
if so, enable this flag.
** Affects: nova
Importance: Undecided
Status: New
** Tags: libvirt
** Tags added: libvirt
--
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Engineering Team, which is subscribed to OpenStack Compute (nova).
https://bugs.launchpad.net/bugs/1484992
Title:
Converting image from qcow2 to raw is slow for images with large
virtual size
Status in OpenStack Compute (nova):
New
Bug description:
In this thread:
http://lists.openstack.org/pipermail/openstack/2015-August/013614.html
[qote]
Running cmd (subprocess): sudo nova-rootwrap /etc/nova/rootwrap.conf qemu-img convert -O raw /var/lib/nova/instances/_base/999f7fff2521e4a7243c9e1d21599fd64a19b42e /dev/openstack-controller01-ky01-vg/5f831046-435c-4636-8b71-a662327b608c_disk
Well, I understand what this step is doing - it's copying raw image to
lvm.
How can we speed it up?
I don't wanna have instance from 100GB image booted for 4 hours
[/quote]
Regardless of how much data is in the source file, qemu-img has to
write out the full virtual size on the target block dev to ensure any
pre-existing data is overwritten. THis may involve writing 100's of GB
of zeros for large images.
qemu-img does has an optimization to let it use 'discard' as a fast
alternative to writing zeros, but this requires that qemu-img has disk
caching disabled , eg -t none. We should investigate to see if this
improves performance for converting large images to block devices, and
if so, enable this flag.
To manage notifications about this bug go to:
https://bugs.launchpad.net/nova/+bug/1484992/+subscriptions
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