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Re: [Qemu-block] import thin provisioned disks with image upload

From: Gianluca Cecchi
Subject: Re: [Qemu-block] import thin provisioned disks with image upload
Date: Fri, 8 Dec 2017 00:34:57 +0100

On Thu, Dec 7, 2017 at 9:33 PM, Nir Soffer <address@hidden> wrote:

For transferring images over http, there is no way to avoid sending 
unused blocks, except compression.

OK, understood

Maybe this file was crated with preallocation=full?

In virt-manager there is not this logic by default.
The default format is qcow2/sparse
When you create/add a disk you can choose "Select or create custom storage":

And then choose a format between:
raw, qcow, qcow2, qed, vmdk, vpc, vdi

In my case it was the default one, so qcow2, as qemu-img correctly detects.

I tested creating qcow2 files with virt manager, and it seems to use
the preallocation=metadata by default (behind your back), I guess 
for improving performance in some cases. oVirt doe not use this
option so we don't have this issue when downloading files.

Ah, ok. I didn't know about this preallocation option of qemu-img
Does your example mean that by default oVirt uses preallocation=off when creating thin provisoned disks?

I hope I convinced you this time ;-)


Yes :- ]  and thanks for the deep an detailed explanation, Nir

Thanks also to Eric for his comments in the other reply


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