Currently when creating VM you can only create thick zvol.
I always use sparse zvols because that’s more storage efficient. But I have to either first create the sparse zvol or change it to sparse later in CLI.
So I suggest that there should be checkbox when creating VM to allow making the zvol sparse.
Or you could make GUI option to convert thick zvols to sparse in datasets page.
Thanks.
They might just use safer setting as tool tip shows
Help: Sparse
Enable to use thin provisioning where disk space for this volume is allocated ‘on demand’ as new writes are received. Use caution when enabling this feature, as writes can fail when the pool is low on space.
I seem to recall there being a technical reason about why this wasn’t implemented, but I might totally be wrong.
Following.
Voted for this. I do this manually, and while I very infrequently build new VMs this would be a really nice addition. Like in the default behavior now, and similar to ESXI, it should still default to “fat” volumes. However, having an option to thin provision shouldn’t require leaving the page and pre-provisioning the zvol each time.
I mean, you can overprovision your pool and run out of space. Its very easy to shoot yourself in the foot if you don’t know what you are doing. But in a world with compression, block cloning and dedupe, thin provisioning’s value can’t be understated.
It also can’t be understated how easy it is to shoot oneself in the foot with dedup.
I’m speaking more about the future when fast dedup is coming in 2.3 
Sorry for not being clear.
Since this request would be in a future version and all.
I believe this is basically done in Fangtooth.
Incus creates sparse volumes by default.
I checked freshly created VM and its zvol has refreservation = none.
It can be optionally set to reserve all the given space with zfs.reserve_space if iX thinks thats safer. I personally like sparse more. But choice is always good.
Yes, I used to always have to create my zvols manually to get sparse… so a “sparse” checkbox in the wizard would’ve been great.
Now that “sparse” is the incus default, maybe there should be a checkbox for “Thick Provision” instead or words to that effect? “Preallocate”?