qemu-devel
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Clarification regarding new qemu-img convert --target-is-zero flag


From: Sam Eiderman
Subject: Clarification regarding new qemu-img convert --target-is-zero flag
Date: Wed, 10 Jun 2020 08:28:29 +0300

Hi,

168468fe19c8 ("qemu-img: Add --target-is-zero to convert") has added a
nice functionality for cloud scenarios:

* Create a virtual disk
* Convert a sparse image (qcow2, vmdk) to the virtual disk using
--target-is-zero
* Use the virtual disk

This saves many unnecessary writes - a qcow2 with 1MB of allocated
data but with 100GB virtual size will be converted efficiently.

However, does this pose a problem if the virtual disk is not zero initialized?

Theoretically - if all unallocated blocks contain garbage - this
shouldn't matter, however what about allocated blocks of zero? Will
convert skip copying allocated zero blocks in the source image to the
target since it assumes that the target is zeroed out first thing?

Sam



reply via email to

[Prev in Thread] Current Thread [Next in Thread]