View source for ChatGPT 有多强：用 ChatGPT 使 qcow2 容量与实际相符

不同类型的Guest机有不同解决方式，基本思路就是用0填充未使用的客户机磁盘空间，然后用qemu-img转换磁盘镜像文件，转换后的磁盘镜像文件将只包含所有已使用的磁盘空间。致谢 [http://bbs.chinaunix.net/thread-3728461-1-1.html 这篇博客]

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|我
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Hi, I have a KVM Windows 10 guest, its C:\ disk is just 50G, but the host /home/user/Documents/win10.qcow2 is 93G. How to let the 93G smaller as actual?
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|ChatGPT
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You can reduce the size of the qcow2 disk image file used by your KVM Windows 10 guest by following these steps:

Note: Make sure you have a backup of your virtual machine or important data before proceeding, as disk resizing operations can be risky.

<b>1. Zero out Unused Space in the Guest</b>: In the Windows 10 guest, you need to zero out the unused space to allow the qcow2 image to be compacted. You can use a tool like "SDelete" (a Microsoft Sysinternals tool) or any other method to zero out free space on your Windows drive.

For example, you can use SDelete to zero out free space on the C: drive:
<syntaxhighlight lang="powershell">
sdelete -z C:
</syntaxhighlight>

<b>2. Shut Down the Guest</b>: Ensure the Windows 10 guest is powered off before proceeding.

<b>3. Resize the Virtual Disk</b>: Use the <code>qemu-img</code> command to resize the qcow2 image file. The following command resizes the image to 50GB (which matches the size of the C:\ disk in your guest):
<syntaxhighlight lang="bash">
qemu-img resize /home/user/Documents/win10.qcow2 50G
</syntaxhighlight>

<b>4. Run a Compaction Operation</b>: You need to perform a compaction operation to reclaim the unused space. Use the `qemu-img` command with the `convert` subcommand and the <code>--shrink</code> option:
<syntaxhighlight lang="bash">
qemu-img convert -O qcow2 /home/user/Documents/win10.qcow2 /home/user/Documents/win10_compacted.qcow2
</syntaxhighlight>

This command creates a compacted copy of your disk image called <code>win10_compacted.qcow2</code>.

<b>5. Replace the Original Disk Image</b>: After the compaction is complete, you can replace the original disk image with the compacted version. Be sure to back up the original image first if you haven't already:
<syntaxhighlight lang="bash">
mv /home/user/Documents/win10_compacted.qcow2 /home/user/Documents/win10.qcow2
</syntaxhighlight>

<b>6. Verify Disk Size</b>: Start your KVM Windows 10 guest and verify that the disk size matches the new, smaller size.

The above steps should help you reduce the size of the qcow2 disk image file to match the actual space used by the guest's C:\ drive.
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