Libguestfs - Jun 2016 - Re: [libvirt-users] virt-sparsify changing the apparent-size of files

On Wed, Jun 22, 2016 at 12:40:40AM -0500, libvirt_users@skagitattic.com
wrote:
> So you are saying when I do the virt-sparsify its converting the image
> from raw to [qcow2]?
No.  virt-sparsify will use the same input and output formats, unless
you use the --convert option.
> I studied the man page for virt-sparsify and tried again with
> the flag "--format raw" (output2.cow2).  This output files looks
as I
> first expected.
> 
> # ls -lrh
> total 4.7G
> -rw-r--r-- 1 root root 790M Jun 14 22:36 output.qcow2
> -rw-r--r-- 1 root root  51G Jun 21 18:34 output2.qcow2
> -rw-r--r-- 1 root root  51G Jun 14 22:30 input.qcow2
> -rw-r--r-- 1 root root 512M Jun 14 22:30 file.img
> # du -sh *
> 0       file.img
> 2.4G    input.qcow2
> 1.6G    output2.qcow2
> 790M    output.qcow2
>
> So I guess it was detecting the source wrong and doing a conversion?
> (As it says "If this is not specified, then the input format is
used."
> in the man page)
> 
> Also seems odd that it is 1.6G rather then the 790M of the output in
> qcow2 format.  Does qcow2 do some compression or something?
I'm really confused about what you actually are doing.

Delete what you've done and start from the beginning.  Describe
exactly how you created the guest.  Use 'qemu-img info' to show the
format of the input file.  Show precisely the virt-sparsify command
you are running.  And use 'qemu-img info' on the output file too.
> Is there any reason to use raw vs non-raw?  From some reading online it
> appears performance is better with raw files.  Is there a downside to
> using raw?
Raw has fewer features, especially no simple snapshotting or support
for backing files.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-builder quickly builds VMs from scratch
http://libguestfs.org/virt-builder.1.html

> Delete what you've done and start from the beginning.  Describe
> exactly how you created the guest.  Use 'qemu-img info' to show the
> format of the input file.  Show precisely the virt-sparsify command
> you are running.  And use 'qemu-img info' on the output file too.
Okay, here goes.  Start off with an install 

    root@testingbox:~ # virt-install --name testimage --memory 512 -l
    'http://ftp.nl.debian.org/debian/dists/jessie/main/installer-amd64/'
    --disk size=50 --nographics -x "console=ttyS0"             

    Starting install...
    Retrieving file
    MANIFEST...
    | 3.3 kB     00:00 ... Retrieving file
    linux...
    | 6.0 MB     00:03 ... Retrieving file
    initrd.gz...
    |  29 MB     00:09 ... Allocating
    'testimage.qcow2'
    |  50 GB     00:00 Creating
    domain...
    |    0 B     00:00 Connected to domain testimage Escape character is
    [    0.000000] Initializing cgroup subsys cpuset [    0.000000]
    Initializing cgroup subsys cpu [    0.000000] Initializing cgroup
    subsys cpuacct [    0.000000] Linux version 3.16.0-4-amd64
    (debian-kernel@lists.debian.org) (gcc version 4.8.4 (Debian 4.8.4-1)
    ) #1 SMP Debian 3.16.7-ckt25-2 (2016-04-08)

....   Many more lines here and it turns interactive.  Suffice it to
say I did a basic minimal install following the prompts.  Nothing
special here.

This created an image that is 2.5G with a 50G apparent size and
identifies as qcow2 as shown below.

    # ls -slh testimage.qcow2 
    2.5G -rw-r--r-- 1 root root 51G Jun 22 20:22 testimage.qcow2

    # qemu-img info testimage.qcow2
    image: testimage.qcow2
    file format: qcow2
    virtual size: 50G (53687091200 bytes)
    disk size: 2.4G
    cluster_size: 65536
    Format specific information:
        compat: 1.1
        lazy refcounts: true

Now we sparsify (/bigtmp is on a larger partition then / to give
virt-sparsify enough room to work with so it does not complain).

    root@testingbox: 08:59 PM # virt-sparsify testimage.qcow2
    testimage1.qcow2 --tmp /bigtmp Input disk virtual size = 53687091200
    bytes (50.0G) Create overlay file in /bigtmp to protect source
    disk ... Examine source disk ...
       100%
⟦▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒⟧
    --:-- Fill free space in /dev/sda1 with zero ... 100%
⟦▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒⟧
    00:00 Clearing Linux swap on /dev/sda5 ... 100%
⟦▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒⟧
    --:-- Copy to destination and make sparse ...

    Sparsify operation completed with no errors.  Before deleting the
    old disk, carefully check that the target disk boots and works
    correctly. 
    root@testingbox: 09:04 PM # 

This image reports still reports as qcow2 however the apparent and real
size is the same.

    # ls -slh testimage1.qcow2 
    1.1G -rw-r--r-- 1 root root 1.1G Jun 22 21:04 testimage1.qcow2

    # qemu-img info testimage1.qcow2
    image: testimage1.qcow2
    file format: qcow2
    virtual size: 50G (53687091200 bytes)
    disk size: 1.1G
    cluster_size: 65536
    Format specific information:
        compat: 1.1
        lazy refcounts: false

If we try it again but specify raw its MUCH faster

    root@testingbox: 09:26 PM # virt-sparsify testimage.qcow2
    testimage2.qcow2 --tmp /bigtmp --format raw Input disk virtual size
    = 53687091200 bytes (50.0G) Create overlay file in /bigtmp to
    protect source disk ... Examine source disk ...
    Copy to destination and make sparse ...

    Sparsify operation completed with no errors.  Before deleting the
    old disk, carefully check that the target disk boots and works
    correctly. 
    root@testingbox: 09:27 PM #

This time it takes up more space and reports real and apparent size
differently.  It still reports as qcow2 with qemu-img.

    # ls -slh testimage2.qcow2 
    1.7G -rw-r--r-- 1 root root 51G Jun 22 21:27 testimage2.qcow2
    # qemu-img info testimage2.qcow2
    image: testimage2.qcow2
    file format: qcow2
    virtual size: 50G (53687091200 bytes)
    disk size: 1.7G
    cluster_size: 65536
    Format specific information:
        compat: 1.1
        lazy refcounts: true

The only things I see different from the finished files is that the raw
one uses a bit more space, the apparent size is not set to the
virtual size on the default sparsify one and the lazy refcounts is
different.

Is there something more detailed then "qemu-img info" that I could
tell
the difference with?
> Raw has fewer features, especially no simple snapshotting or support
> for backing files.
Is simple snapshotting using qemu-img snapshot or something else?  I
tried making a snapshot with both test images and they both appeared to
work.

    # qemu-img snapshot -c test  testimage1.qcow2 
    # qemu-img snapshot -c test  testimage2.qcow2 
    # qemu-img info  testimage2.qcow2 
    image: testimage2.qcow2
    file format: qcow2
    virtual size: 50G (53687091200 bytes)
    disk size: 1.7G
    cluster_size: 65536
    Snapshot list:
    ID        TAG                 VM SIZE                DATE       VM
     CLOCK 1         test                      0 2016-06-22 22:41:52
     00:00:00.000 Format specific information:
        compat: 1.1
        lazy refcounts: true
    # qemu-img info  testimage1.qcow2 
    image: testimage1.qcow2
    file format: qcow2
    virtual size: 50G (53687091200 bytes)
    disk size: 1.1G
    cluster_size: 65536
    Snapshot list:
    ID        TAG                 VM SIZE                DATE       VM
     CLOCK 1         test                      0 2016-06-22 22:41:44
     00:00:00.000 Format specific information:
        compat: 1.1
        lazy refcounts: false

The backing file thing appeared to work on the 2nd one where I
specified raw as well.
    # qemu-img create -f qcow2 -b testimage2.qcow2  backup-test2.qcow2
    Formatting 'backup-test2.qcow2', fmt=qcow2 size=53687091200
    backing_file='testimage2.qcow2' encryption=off cluster_size=65536
    lazy_refcounts=off 
    # ls -lsh
    backup-test2.qcow2 196K -rw-r--r-- 1 root root 193K Jun 22 22:48
    backup-test2.qcow2

Though perhaps if I actually tried to add them and boot it up something
would not work?


Keelan



On Wed, 22 Jun 2016 09:58:29 +0100
"Richard W.M. Jones" <rjones@redhat.com> wrote:
> On Wed, Jun 22, 2016 at 12:40:40AM -0500,
> libvirt_users@skagitattic.com wrote:
> > So you are saying when I do the virt-sparsify its converting the
> > image from raw to [qcow2]?  
> 
> No.  virt-sparsify will use the same input and output formats, unless
> you use the --convert option.
> 
> > I studied the man page for virt-sparsify and tried again with
> > the flag "--format raw" (output2.cow2).  This output files
looks as
> > I first expected.
> > 
> > # ls -lrh
> > total 4.7G
> > -rw-r--r-- 1 root root 790M Jun 14 22:36 output.qcow2
> > -rw-r--r-- 1 root root  51G Jun 21 18:34 output2.qcow2
> > -rw-r--r-- 1 root root  51G Jun 14 22:30 input.qcow2
> > -rw-r--r-- 1 root root 512M Jun 14 22:30 file.img
> > # du -sh *
> > 0       file.img
> > 2.4G    input.qcow2
> > 1.6G    output2.qcow2
> > 790M    output.qcow2
> >
> > So I guess it was detecting the source wrong and doing a conversion?
> > (As it says "If this is not specified, then the input format is
> > used." in the man page)
> > 
> > Also seems odd that it is 1.6G rather then the 790M of the output in
> > qcow2 format.  Does qcow2 do some compression or something?  
> 
> I'm really confused about what you actually are doing.
> 
> Delete what you've done and start from the beginning.  Describe
> exactly how you created the guest.  Use 'qemu-img info' to show the
> format of the input file.  Show precisely the virt-sparsify command
> you are running.  And use 'qemu-img info' on the output file too.
> 
> > Is there any reason to use raw vs non-raw?  From some reading
> > online it appears performance is better with raw files.  Is there a
> > downside to using raw?  
> 
> Raw has fewer features, especially no simple snapshotting or support
> for backing files.
> 
> Rich.
>

On Wed, 2016-06-22 at 17:56 -0500, libvirt_users@skagitattic.com
wrote:
> If we try it again but specify raw its MUCH faster
> 
>     root@testingbox: 09:26 PM # virt-sparsify testimage.qcow2
>     testimage2.qcow2 --tmp /bigtmp --format raw Input disk virtual size
>     = 53687091200 bytes (50.0G) Create overlay file in /bigtmp to
>     protect source disk ... Examine source disk ...
>     Copy to destination and make sparse ...
> 
>     Sparsify operation completed with no errors.  Before deleting the
>     old disk, carefully check that the target disk boots and works
>     correctly. 
>     root@testingbox: 09:27 PM #
> 
> This time it takes up more space and reports real and apparent size
> differently.  It still reports as qcow2 with qemu-img.
> 
>     # ls -slh testimage2.qcow2 
>     1.7G -rw-r--r-- 1 root root 51G Jun 22 21:27 testimage2.qcow2
>     # qemu-img info testimage2.qcow2
>     image: testimage2.qcow2
>     file format: qcow2
>     virtual size: 50G (53687091200 bytes)
>     disk size: 1.7G
>     cluster_size: 65536
>     Format specific information:
>         compat: 1.1
>         lazy refcounts: true
The '--format' option is to specify the image format for the
input image. If you want the *output* image to be raw, you'll
have to use '--convert raw'.

-- Andrea Bolognani / Red Hat / Virtualization

On Wed, Jun 22, 2016 at 05:56:09PM -0500, libvirt_users@skagitattic.com
wrote:
> > Delete what you've done and start from the beginning.  Describe
> > exactly how you created the guest.  Use 'qemu-img info' to
show the
> > format of the input file.  Show precisely the virt-sparsify command
> > you are running.  And use 'qemu-img info' on the output file
too.
> 
> Okay, here goes.  Start off with an install 
> 
>     root@testingbox:~ # virt-install --name testimage --memory 512 -l
>    
'http://ftp.nl.debian.org/debian/dists/jessie/main/installer-amd64/'
>     --disk size=50 --nographics -x "console=ttyS0"             
> 
>     Starting install...
>     Retrieving file
>     MANIFEST...
>     | 3.3 kB     00:00 ... Retrieving file
>     linux...
>     | 6.0 MB     00:03 ... Retrieving file
>     initrd.gz...
>     |  29 MB     00:09 ... Allocating
>     'testimage.qcow2'
>     |  50 GB     00:00 Creating
>     domain...
>     |    0 B     00:00 Connected to domain testimage Escape character is
>     [    0.000000] Initializing cgroup subsys cpuset [    0.000000]
>     Initializing cgroup subsys cpu [    0.000000] Initializing cgroup
>     subsys cpuacct [    0.000000] Linux version 3.16.0-4-amd64
>     (debian-kernel@lists.debian.org) (gcc version 4.8.4 (Debian 4.8.4-1)
>     ) #1 SMP Debian 3.16.7-ckt25-2 (2016-04-08)
> 
> ....   Many more lines here and it turns interactive.  Suffice it to
> say I did a basic minimal install following the prompts.  Nothing
> special here.
> 
> This created an image that is 2.5G with a 50G apparent size and
> identifies as qcow2 as shown below.
> 
>     # ls -slh testimage.qcow2 
>     2.5G -rw-r--r-- 1 root root 51G Jun 22 20:22 testimage.qcow2
> 
>     # qemu-img info testimage.qcow2
>     image: testimage.qcow2
>     file format: qcow2
>     virtual size: 50G (53687091200 bytes)
>     disk size: 2.4G
>     cluster_size: 65536
>     Format specific information:
>         compat: 1.1
>         lazy refcounts: true
> 
> Now we sparsify (/bigtmp is on a larger partition then / to give
> virt-sparsify enough room to work with so it does not complain).
> 
>     root@testingbox: 08:59 PM # virt-sparsify testimage.qcow2
>     testimage1.qcow2 --tmp /bigtmp Input disk virtual size = 53687091200
>     bytes (50.0G) Create overlay file in /bigtmp to protect source
>     disk ... Examine source disk ...
>        100%
>
⟦▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒⟧
>     --:-- Fill free space in /dev/sda1 with zero ... 100%
>
⟦▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒⟧
>     00:00 Clearing Linux swap on /dev/sda5 ... 100%
>
⟦▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒⟧
>     --:-- Copy to destination and make sparse ...
> 
>     Sparsify operation completed with no errors.  Before deleting the
>     old disk, carefully check that the target disk boots and works
>     correctly. 
>     root@testingbox: 09:04 PM # 
> 
> This image reports still reports as qcow2 however the apparent and real
> size is the same.
> 
>     # ls -slh testimage1.qcow2 
>     1.1G -rw-r--r-- 1 root root 1.1G Jun 22 21:04 testimage1.qcow2
> 
>     # qemu-img info testimage1.qcow2
>     image: testimage1.qcow2
>     file format: qcow2
>     virtual size: 50G (53687091200 bytes)
>     disk size: 1.1G
>     cluster_size: 65536
>     Format specific information:
>         compat: 1.1
>         lazy refcounts: false
virt-sparsify saved about 1.3 GB of disk space (2.4G -> 1.1G).
> If we try it again but specify raw its MUCH faster
> 
>     root@testingbox: 09:26 PM # virt-sparsify testimage.qcow2
>     testimage2.qcow2 --tmp /bigtmp --format raw
This is incorrect usage.  You've told virt-sparsify that the input
image is raw.  But it's not raw, it's qcow2.

In any case, virt-sparsify opened the image as raw, couldn't make any
sense of it (it appears to virt-sparsify to be random data, not a disk
image), and so it cannot sparsify it properly.  This is "quicker" only
because virt-sparsify didn't do any sparsification of filesystems,
because it couldn't see the filesystems.
> This time it takes up more space and reports real and apparent size
> differently.  It still reports as qcow2 with qemu-img.
> 
>     # ls -slh testimage2.qcow2 
>     1.7G -rw-r--r-- 1 root root 51G Jun 22 21:27 testimage2.qcow2
>     # qemu-img info testimage2.qcow2
>     image: testimage2.qcow2
>     file format: qcow2
>     virtual size: 50G (53687091200 bytes)
>     disk size: 1.7G
Looks like virt-sparsify still found some clusters containing all
zeroes which it could trim, even though it didn't know how to read the
disk.

Anyway, the moral is, don't misinform virt-sparsify of the format
of your input image.

If what you really intended to do was to convert the format from qcow2
to raw, you should use '--convert raw' instead.
> The only things I see different from the finished files is that the raw
> one uses a bit more space, the apparent size is not set to the
> virtual size on the default sparsify one and the lazy refcounts is
> different.
> 
> Is there something more detailed then "qemu-img info" that I
could tell
> the difference with?
qemu-img info is the correct tool to use.
> > Raw has fewer features, especially no simple snapshotting or support
> > for backing files.
I wrote this thinking you were talking about actual raw format disks,
not about qcow2 but where you've misinformed virt-sparsify about the
format.
> Is simple snapshotting using qemu-img snapshot or something else?  I
> tried making a snapshot with both test images and they both appeared to
> work.
http://wiki.qemu.org/Documentation/CreateSnapshot
>     # qemu-img snapshot -c test  testimage1.qcow2 
>     # qemu-img snapshot -c test  testimage2.qcow2 
>     # qemu-img info  testimage2.qcow2 
>     image: testimage2.qcow2
>     file format: qcow2
>     virtual size: 50G (53687091200 bytes)
>     disk size: 1.7G
>     cluster_size: 65536
>     Snapshot list:
>     ID        TAG                 VM SIZE                DATE       VM
>      CLOCK 1         test                      0 2016-06-22 22:41:52
>      00:00:00.000 Format specific information:
>         compat: 1.1
>         lazy refcounts: true
This works because testimage2.qcow2 is still in qcow2 format.

Anyway, use the correct --format option.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
libguestfs lets you edit virtual machines.  Supports shell scripting,
bindings from many languages.  http://libguestfs.org