On 06/19/2018 03:37 PM, Gionatan Danti wrote: > Il 19-06-2018 20:14 Cole Robinson ha scritto: >> If you change the disk image format from qcow2 to raw in >> Edit->Preferences, then new disk images are set to fully allocated raw. >> Check the image details with 'qemu-img info $filename' to confirm. So I >> think by default we are doing what you want? >> >> - Cole > > Er, the point is that I would really like to have a *sparse* RAW image > file. On older virt-manager, unchecking "allocate entire disk" was what > I normally used. Auto-allocating all disk space without a mean to avoid > that has two main drawbacks: > - you can't have sparse/thin volumes; > - allocating on a fallocate-less filesystem is excruciatingly slow and > cause of unneeded wear on SSDs. > > Why using a sparse RAW image rather than a Qcow2 image? Basically: > - RAW disks are easier to handle/inspect in case something goes wrong; > - avoid double CoW on CoW-enabled filesystems (eg: ZFS, btrfs); > - better performance (no Qcow2 L2 chunk cache range, etc). > > It is worth nothing that oVirt (and RHEV) uses (sparse or allocated, > based on user selection) base RAW files with eventual Qcow2 overlays for > snapshots. > Sorry, I misunderstood. You can still achieve what you want but it's more clicks: new vm, manage storage, add volume, and select raw volume with whatever capacity you want but with 0 allocation. qcow2 is the default for virt-manager because it enables features like snapshots out of the box. The main motivation I have largely heard for wanting raw over qcow2 is performance, but then using sparse raw actually makes raw less performant, so it's kind of a weird middle ground. For that reason I don't think it warrants adding back the checkbox to the new VM UI since I think it's a fairly obscure use case, and it can be achieved through the 'manage storage' wizard albeit with more clicks - Cole _______________________________________________ libvirt-users mailing list libvirt-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvirt-users
