qcow2 file size on NFS shared storage

DynFi User

DynFi User

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Apr 18, 2016
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Hello,

I am trying to figure out how things are working when related to disk size and disk image and real disk size.

I have an NFS shared storage with 10T of disk space.
This storage is a FreeNAS ZFS storage and is available on all nodes of my cluster (shared using NFS).

The size of the qcow2 disk on my NFS server is the following :

[root@jaws] /mnt/data/home/gregober# ls -alh /mnt/data/kvm/images/127/
total 4174686
drwxr----- 2 root wheel 3B Sep 15 16:46 ./
drwxr-xr-x 7 root wheel 7B Sep 15 16:46 ../
-rw-r--r-- 1 root wheel 9.8G Sep 15 17:27 vm-127-disk-1.qcow2
​

When I am inside the server I have a totally different picture :


gregober@fred:~$ df -h
Filesystem Size Used Avail Use% Mounted on
udev 478M 0 478M 0% /dev
tmpfs 100M 5.8M 94M 6% /run
/dev/vda1 62G 23G 37G 39% /
tmpfs 497M 4.0K 497M 1% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 497M 0 497M 0% /sys/fs/cgroup
tmpfs 100M 0 100M 0% /run/user/1002
tmpfs 100M 0 100M 0% /run/user/1001​




So my simple question is : where are the missing bits ??

I wrote two files of 10G each inside the KVM container and the size of the qcow2 image didn't move at all.


I have resized in Proxmox GUI the file size of the KVM image and put it 60G more… Still no change in the qcow2 file…


I am really perplex about all this : the size of my data inside the KVM is bigger than the reported file size of my qcow2 disk ?!


Could someone light my candle ?
 
dd if=/dev/zero of=10G2 bs=1M count=10000

Yes zeroes !
 
So all in all I should be safe with my Qcow2 being 10G and my KVM thinking It is 67G ?

I am testing It with /dev/urandom

Will also read the pointer !
 
I have written a 12G file using dd and /dev/urandom and the size of my qcow2 image hasn't move a bit ?!

I am really perplex :

  1. where are the data stored ?
  2. what if my data get bigger than my storage ?
  3. How can a virtualized file system be bigger than the image which is supposed to contain the data ?

I am asking all this because we are about to deploy critical servers using this method and, I need to avoid any problem with this deployment.
 
No, It is not possible that I am checking the wrong file.
 
could you post the output of "qemu-img info /mnt/data/kvm/images/127/vm-127-disk-1.qcow2" and "qm config 127"? I am pretty sure that we are missing something along the way..
 
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