Gionatan Danti
2018-Jun-19 23:06 UTC
Re: [libvirt-users] Reintroduce "allocate entire disk" checkbox on virt-manager
Il 19-06-2018 22:16 Cole Robinson ha scritto:> 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.Sure, but the automatic disk creation is very handy and much less error prone. As it is now, if using a fallocate-less filesystem (eg: ZFS) and *not* selecting to create a custom disk, you risk waiting minutes or hours for libvirt to fully allocate the image by writing 0s to the disk file. This can wreck havok on SSDs and other eundurance-limited medium.> 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 > > - ColeOn CoW filesystems, sparse RAW files are faster then Qcow2 ones. Moreover, avoiding double CoW is important for SSDs (which have limited lifespan). Even on XFS, sparse RAW files should be faster in the long run than Qcow2 files, due to no weird limitation on L2 chunk cache size. I found the checkbox quite self-explanatory and very handy. Any chances to reconsider your decision? Thanks. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti@assyoma.it - info@assyoma.it GPG public key ID: FF5F32A8
Gionatan Danti
2018-Jun-22 17:47 UTC
Re: [libvirt-users] Reintroduce "allocate entire disk" checkbox on virt-manager
Il 20-06-2018 01:06 Gionatan Danti ha scritto:> Il 19-06-2018 22:16 Cole Robinson ha scritto: >> 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. > > Sure, but the automatic disk creation is very handy and much less error > prone. > As it is now, if using a fallocate-less filesystem (eg: ZFS) and *not* > selecting to create a custom disk, you risk waiting minutes or hours > for libvirt to fully allocate the image by writing 0s to the disk > file. This can wreck havok on SSDs and other eundurance-limited > medium. > >> 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 > > On CoW filesystems, sparse RAW files are faster then Qcow2 ones. > Moreover, avoiding double CoW is important for SSDs (which have > limited lifespan). Even on XFS, sparse RAW files should be faster in > the long run than Qcow2 files, due to no weird limitation on L2 chunk > cache size. > > I found the checkbox quite self-explanatory and very handy. Any > chances to reconsider your decision? > Thanks.Hi, sorry for the bump... any feedback about that? Thanks. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti@assyoma.it - info@assyoma.it GPG public key ID: FF5F32A8
Cole Robinson
2018-Jun-26 21:49 UTC
Re: [libvirt-users] Reintroduce "allocate entire disk" checkbox on virt-manager
On 06/19/2018 07:06 PM, Gionatan Danti wrote:> Il 19-06-2018 22:16 Cole Robinson ha scritto: >> 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. > > Sure, but the automatic disk creation is very handy and much less error > prone. > As it is now, if using a fallocate-less filesystem (eg: ZFS) and *not* > selecting to create a custom disk, you risk waiting minutes or hours for > libvirt to fully allocate the image by writing 0s to the disk file. This > can wreck havok on SSDs and other eundurance-limited medium. > >> 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 > > On CoW filesystems, sparse RAW files are faster then Qcow2 ones. > Moreover, avoiding double CoW is important for SSDs (which have limited > lifespan). Even on XFS, sparse RAW files should be faster in the long > run than Qcow2 files, due to no weird limitation on L2 chunk cache size. > > I found the checkbox quite self-explanatory and very handy. Any chances > to reconsider your decision?I see it as another test case and larger UI surface in the common path for something that will save clicks for a corner case. I still don't see it asworth exposing in the UI. - Cole
Gionatan Danti
2018-Jun-28 10:35 UTC
Re: [libvirt-users] Reintroduce "allocate entire disk" checkbox on virt-manager
Il 26-06-2018 23:49 Cole Robinson ha scritto:> I see it as another test case and larger UI surface in the common path > for something that will save clicks for a corner case. I still don't > see > it asworth exposing in the UI. > > - ColeI can not force this decision, obviously. However, let me recap why I found it important to have the "allocate disk now" checkbox: - RAW files, even sparse one, are faster than Qcow2 files in the long run (ie: when block allocation is >8 GB); - Qcow2 snapshots have significant gotchas (ie: the guest is suspended during the snapshot), while using RAW files will at least prevent using virt-manager snapshot feature without thinking; - on CoW filesystems, using Qcow2 files will means *double* CoW with a) reduced performance and b) more wear on SSDs; - on filesystems not supporting fallocate, libvirtd reverts to "write zeroes to the entire file) which is both a) very slow and b) detrimental to SSDs life; - most other virtualization platform (old virt-manager and current oVirt included) split the choice of file format from the allocation policy. I 100% agree that, using the custom disk creation mask, what I ask it entirely possible with virt-manager today. However, it would be *very* handy to have the checkbox back in the VM wizard itself. Would opening a BZ ticket at least reopen the possibility to reconsider that decision? Thanks anyway. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti@assyoma.it - info@assyoma.it GPG public key ID: FF5F32A8
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