[2024-feb-29] Sad news: Eric Layton aka Nocturnal Slacker aka vtel57 passed away on Feb 26th, shortly after hospitalization. He was one of our Wiki's most prominent admins. He will be missed.
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howtos:emulators:kvm_libvirt_qemu_quirks_tips_etc [2022/05/16 10:29 (UTC)] – [Increasing guest console/framebuffer resolution] zeebra | howtos:emulators:kvm_libvirt_qemu_quirks_tips_etc [2023/11/05 20:49 (UTC)] – [QEMU QCOW2 freed virtual disk space doesn't shrink image] zeebra | ||
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+ | ===== QEMU QCOW2 freed virtual disk space doesn' | ||
+ | |||
+ | === Background === | ||
+ | |||
+ | Let's say you have a faulty setup for the virtual disk and QCOW2 images. If everything was working (dicard/ | ||
+ | |||
+ | Always remember to have proper backups (backup your QCOW2 image before proceeding). | ||
+ | |||
+ | === How to manually shrink the QCOW2 image to reflect the content on the virtual disk image === | ||
+ | |||
+ | 1. Inside the virtual machine, write zeroes to a file until the virtual disk is full. In a terminal: | ||
+ | < | ||
+ | dd if=/ | ||
+ | </ | ||
+ | |||
+ | 2. Delete the new file (/ | ||
+ | 3. Shut down the virtual machine | ||
+ | |||
+ | 4. You can use the convert image function to basically move the current image into a new image (convert from qcow2 to qcow2), and it will reflect the actual size of content (disregard zeroes) | ||
+ | < | ||
+ | qemu-img convert -O qcow2 oldimage.qcow2 newimage.qcow2 | ||
+ | </ | ||
+ | |||
+ | This is just a workaround. Ideally you should have your virtual machine setup with a functional discard inside the virtual machine to write zeroes to the areas of deleted files/ | ||
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