[libvirt-users] Make discard='unmap' the default?

[Ian Pilcher]

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?)

Thanks!

[Daniel P. Berrangé]

Post by Ian Pilcher
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.

Regards,
Daniel

[Ian Pilcher]

Post by Daniel P. Berrangé

Post by Ian Pilcher
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.

I'm using virt-manager. I was under the impression that it gets its
"hypervisor default" device types from libvirt.

[Daniel P. Berrangé]

Post by Ian Pilcher

Post by Daniel P. Berrangé

Post by Ian Pilcher
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.

I'm using virt-manager. I was under the impression that it gets its
"hypervisor default" device types from libvirt.

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.

Regards,
Daniel

[Ian Pilcher]

Post by Daniel P. Berrangé
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.

[Daniel P. Berrangé]

Post by Ian Pilcher

Post by Daniel P. Berrangé
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

Regards,
Daniel

[Pavel Hrdina]

Post by Daniel P. Berrangé

Post by Ian Pilcher

Post by Daniel P. Berrangé
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

There is a way how to set few defaults (Edit->Preferences->New VM)
but this one is not there. Creating RFE sounds reasonable.

Pavel