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Re: [Qemu-devel] [PATCH 8/8] docs: add mirroring to live block operation
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH 8/8] docs: add mirroring to live block operations |
Date: |
Fri, 13 Apr 2012 11:09:03 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120329 Thunderbird/11.0.1 |
On 04/13/2012 10:23 AM, Paolo Bonzini wrote:
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
> docs/live-block-ops.txt | 38 +++++++++++++++++++++++++++++++-------
> 1 file changed, 31 insertions(+), 7 deletions(-)
>
>
> +Live block migration
> +====================
> +
> +Migrating an in use image to another destination in the filesystem
> +is done through image mirroring. The idea is to execute
> +'drive_mirror virtio0 /new-path/disk.img qcow2' while the guest
> +is running. The topmost image ([D] in the example above) will
> +be copied to the given path, and the two can be kept in sync.
> +
> +Progress can be monitored using 'info block-jobs'. Once this command
> +reports something like
maybe: s/reports something like/reports completion equal to size, as in/
> +
> + Type mirror, device virtio0: Completed 1048576000 of 1048576000 bytes
> +
> +it is possible to switch to the destination using
> +
> +(qemu) drive_reopen virtio0 /new-path/disk.img
> +
> +This assumes that all images A/B/C are also present under /new-path
> +or. An image can be omitted from the destination if one of the images
Dangling sentence.
> +refers to its backing file using an absolute path.
I think you need to rework this paragraph. It sounds like you are
trying to state whether /new-path/disk.img will have an absolute backing
file path (in which case, it is reusing C, and therefore A and B, from
the same locations found when originally opening D), or whether
/new-path/disk.img will have a relative backing path (this would be
either through a relative-paths mode option, or through the reuse of an
existing file intentionally created with a relative backing path), in
which case the reopen now resolves the backing path locally so A, B, and
C must all be present at /new-path for the reopen to succeed.
> +
> +
> Live block copy
> ===============
>
> To copy an in use image to another destination in the filesystem, one
> -should create a live snapshot in the desired destination, then stream
> -into that image. Example:
> -
> -(qemu) snapshot_blkdev ide0-hd0 /new-path/disk.img qcow2
> +can also use mirroring with the -f option.
>
> -(qemu) block_stream ide0-hd0
> +(qemu) drive_mirror -f virtio0 /new-path/disk.img qcow2
>
> +Note that if one image in the chain is in raw format, the
> +resulting copy might not be thin-provisioned anymore, depending on
> +the underlying file system.
>
> +It is also possible to use raw as the format of the destination image.
> +Converting an image to raw will properly support thin provisioning.
Do you need to mention the use of block_job_cancel needed at the point
where you are ready to stop qemu from writing into the copy?
--
Eric Blake address@hidden +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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- [Qemu-devel] [PATCH 5/8] block: add drive-mirror command, (continued)
- [Qemu-devel] [PATCH 4/8] block: add mirror job, Paolo Bonzini, 2012/04/13
- [Qemu-devel] [PATCH 8/8] docs: add mirroring to live block operations, Paolo Bonzini, 2012/04/13
- Re: [Qemu-devel] [PATCH 8/8] docs: add mirroring to live block operations,
Eric Blake <=
- Re: [Qemu-devel] [PATCH 8/8] docs: add mirroring to live block operations, Paolo Bonzini, 2012/04/13
- Re: [Qemu-devel] [PATCH 8/8] docs: add mirroring to live block operations, Eric Blake, 2012/04/13
- Re: [Qemu-devel] [PATCH 8/8] docs: add mirroring to live block operations, Paolo Bonzini, 2012/04/13
- Re: [Qemu-devel] [PATCH 8/8] docs: add mirroring to live block operations, Eric Blake, 2012/04/13
- Re: [Qemu-devel] [PATCH 8/8] docs: add mirroring to live block operations, Paolo Bonzini, 2012/04/16
[Qemu-devel] [PATCH 7/8] block: add witness argument to drive-reopen, Paolo Bonzini, 2012/04/13