Re: [Qemu-devel] [PATCH v1 00/13] qcow2: space preallocation and COW improvements

[Eric Blake]

On 05/19/2017 04:34 AM, Anton Nefedov wrote:
> This pull request is to address a few performance problems of qcow2 format:
> 
>   1. non cluster-aligned write requests (to unallocated clusters) explicitly
>     pad data with zeroes if there is no backing data. This can be avoided
>     and the whole clusters are preallocated and zeroed in a single
>     efficient write_zeroes() operation, also providing better host file
>     continuity
> 
>   2. moreover, efficient write_zeroes() operation can be used to preallocate
>     space megabytes ahead which gives noticeable improvement on some storage
>     types (e.g. distributed storages where space allocation operation is
>     expensive)
> 
>   3. preallocating/zeroing the clusters in advance makes possible to enable
>     simultaneous writes to the same unallocated cluster, which is beneficial
>     for parallel sequential write operations which are not cluster-aligned
> 
> Performance test results are added to commit messages (see patch 3, 12)

And now Berto has posted parallel patches. I'm not sure which ones to
focus on, or if you can work it out between you on the best approach
forward...

https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg05236.html

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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