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[Qemu-discuss] creating VM disk with

From: Nguyễn Thùy Linh
Subject: [Qemu-discuss] creating VM disk with
Date: Fri, 29 Apr 2016 16:02:27 +0200


I am working on booting a VM using qemu. My scenario: I have n VMs, first, I boot the 1st VM completely, then boot the rest VMs at the same time. 

I found out there are two ways to create a VM disk from image:
  1. using qemu-img convert: this command will create a disk with the same size of image. When VM is booted, VM use this disk to load OS. If I have many VMs, each VM owns an independent disk.
  2. using qemu-img create: this command will create an empty VM disk. When VM is booted, qemu will load necessary kernel data from image to this disk. If I have many VMs, each VM has an empty disk.
All VM disks is created from one image. What I expect is, in the 2nd way, when I boot the 1st VM, the image will be cached in memory, then, the other VMs will load image from cache. Therefore, the boot time of the other VMs might be faster.

However, when I run this experiment, I observe that the image is not cached in the memory. Every VM has to read kernel data from physical disk (where image stored).

My question is if image is cached in memory or not?

Thank you,

Linh Nguyen

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