On Thu, May 31, 2018 at 02:34:15PM -0500, Ian Pilcher wrote: > Is it possible to make discard='unmap' the default for virtio-scsi > disks? (Related, is it possible to make virtio-scsi the default disk > type, rather than virtio-blk?) This is really a question for whatever management tool you're using with libvirt, since it is essentially defining an opinionated usage policy.

Yes, it inherits some defaults to libvirt and/or QEMU. If those are not suitable for some reason, then virt-manager needs to override it. The decision about whether to enable discard or not is a policy decision that doesn't have a single perfect answer. So changing it in libvirt might make it better for you, but worse for someone else. Libvirt does not want to get into such debates, so leaves such decisions for the app above to make, where there may well be more global context/knowledge allowing a better choice.

On Fri, Jun 01, 2018 at 08:37:30AM -0500, Ian Pilcher wrote: > On 06/01/2018 08:14 AM, Daniel P. Berrangé wrote: > > Yes, it inherits some defaults to libvirt and/or QEMU. If those are not > > suitable for some reason, then virt-manager needs to override it. The > > decision about whether to enable discard or not is a policy decision > > that doesn't have a single perfect answer. So changing it in libvirt > > might make it better for you, but worse for someone else. Libvirt does > > not want to get into such debates, so leaves such decisions for the app > > above to make, where there may well be more global context/knowledge > > allowing a better choice. > > To be clear, I'm not suggesting that the "default defaults" be changed, > I would just like to change the default on my personal system. > > It sounds like you're saying that libvirt expects virt-manager to > override these settings (if it wants to), but virt-manager doesn't > provide any way to do so, since it just uses the defaults from libvirt/ > QEMU. Yes, exactly. IOW, perhaps file an RFE against virt-manager