Il giorno mer 28 nov 2018 alle ore 14:41 Eric Blake <eblake@xxxxxxxxxx> ha scritto: > > On 11/28/18 2:29 AM, Vincenzo Romano wrote: > > >>> How do you request qcow3? According to the edit history of https:// > >>> wiki.qemu.org/Features/Qcow3 , qcow3 should be many years old but the manpage > >>> of qemu-img on my current system does not mention qcow3. > >> > >> You probably mean qcow2v3. It is also spelled as 'qemu-img create -o > >> compat=1.1' (newer qemu-img also recognizes the spelling compat=v3), as > >> opposed to the older 'qemu-img create -o compat=0.10' or v2 images. But > >> if the virt-manager gui is specifically calling it qcow3, rather than > >> qcow2v3, then that's a needless confusion that we should fix in the gui. > > > > Hi. > > I relied on the "file" tool provided by Archlinux. It says "QCOW3" as > > the file type by its contents. > > No, it says "QCOW Image (v3)", and means qcow2v3, because file is not > distinguishing between 'qcow' and 'qcow2'. It would be worth a bug > report to the 'file' database maintainers to update their magic file to > distinguish 'qcow' (the old v1 that is no longer used anywhere) from > 'qcow2' (with both 'qcow2 v2' and 'qcow2 v3' flavors). Understood. Thanks for the insight. > > So I have manually created another storage image file by command line with: > > > > qemu-img create -f qcow2 ./windows2008-d1.qcow 250G > > > > The other image file (the sparse one) has been created by virt-manager/libvirt. > > So virt-manager probably requested preallocation when it created the file. I suspect so. > > Then I have run these commands: > > > > ~ ls -l > > total 2,9G > > drwxrwx--- 2 vmanager vmanager 62 2018-11-27 13:14:36 . > > drwxr-xr-x 7 vmanager vmanager 152 2018-11-26 12:47:06 .. > > -rw-rw---- 1 libvirt-qemu kvm 6,1G 2018-11-28 09:19:22 ubuntu18.04 > > -rw-rw---- 1 libvirt-qemu kvm 196K 2018-11-27 13:14:36 windows2008-d1.qcow > > [root@host01 /home/vmanager/storage] file * > > ubuntu18.04: QEMU QCOW Image (v3), 6442450944 bytes > > windows2008-d1.qcow: QEMU QCOW Image (v3), 268435456000 bytes > > ~ du * > > 3015704 ubuntu18.04 > > 196 windows2008-d1.qcow > > > > Both files have the same type but while "ubuntu18.04" is clearly a > > sparse file, "windows2008-d1.qcow" is not. > > You've got that backwards. ubuntu18.04 is sized to use 6.1G of host > space while providing 6G of data to the guest, so it is preallocated and > does not appear to be sparse (although du would let you know if the file > has holes as part of its preallocated space, such that the host size is > large but the on-disk usage is still sparse). windows2008-d1.qcow is > occupying very little host space, while advertising 250G to the guest, > so it is DEFINITELY sparse. Hmmm... I think I don't agree- The file "ubuntu18.04" is said to be 6.1GB while actually eating 3015704 kB (~ 3GB) in the file system. It's a sparse file, indeed. The file "windows2008-d1.qcow" is said to be 196 kB and that's the actual room used on the file system. That's NOT a sparse file. It's the usual QCOW file I am accustomed with that grows both in file size and in storage eaten. I think the former is a "somewhat special" QCOW file. > > I doesn't make any real difference. It just puzzles me. > > The difference is whether you choose to preallocate an image. There are > performance tradeoffs for doing so (a preallocated image is faster than > a sparse one when it comes to writing to previously unused portions of > the disk, but occupies more host space as a result - also, a > preallocated image tends to have less fragmentation and less chance of > hitting ENOSPC). Yes, but I've never seen (so far) a sparse QCOW file. After all, QCOW was introduced also to let users use file systems not supporting "sparse files". -- Vincenzo Romano - NotOrAnd.IT Information Technologies -- NON QVIETIS MARIBVS NAVTA PERITVS _______________________________________________ virt-tools-list mailing list virt-tools-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/virt-tools-list
