** Changed in: qemu-kvm (Ubuntu)
Status: Confirmed => Triaged
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https://bugs.launchpad.net/bugs/814222
Title:
kvm cannot use vhd files over 127GB
Status in QEMU:
New
Status in “qemu-kvm” package in Ubuntu:
Triaged
Bug description:
The primary use case for using vhds with KVM is to perform a
conversion to a raw image file so that one could move from Hyper-V to
Linux-KVM. See more on this http://blog.allanglesit.com/2011/03
/linux-kvm-migrating-hyper-v-vhd-images-to-kvm/
# kvm-img convert -f raw -O vpc /root/file.vhd /root/file.img
The above works great if you have VHDs smaller than 127GB, however if
it is larger, then no error is generated during the conversion
process, but it appears to just process up to that 127GB barrier and
no more. Also of note. VHDs can also be run directly using KVM if
they are smaller than 127GB. VHDs can be read and function well using
virtualbox as well as hyper-v, so I suspect the problem lies not with
the VHD format (since that has a 2TB limitation). But instead with
how qemu-kvm is interpreting them.
BORING VERSION INFO:
# cat /etc/issue
Ubuntu 11.04 \n \l
# uname -rmiv
2.6.38-8-server #42-Ubuntu SMP Mon Apr 11 03:49:04 UTC 2011 x86_64 x86_64
# apt-cache policy kvm
kvm:
Installed: 1:84+dfsg-0ubuntu16+0.14.0+noroms+0ubuntu4.1
Candidate: 1:84+dfsg-0ubuntu16+0.14.0+noroms+0ubuntu4.1
Version table:
*** 1:84+dfsg-0ubuntu16+0.14.0+noroms+0ubuntu4.1 0
500 http://apt.sonosite.com/ubuntu/ natty-updates/main amd64 Packages
500 http://apt.sonosite.com/ubuntu/ natty-security/main amd64 Packages
100 /var/lib/dpkg/status
1:84+dfsg-0ubuntu16+0.14.0+noroms+0ubuntu4 0
500 http://apt.sonosite.com/ubuntu/ natty/main amd64 Packages
# apt-cache policy libvirt-bin
libvirt-bin:
Installed: 0.8.8-1ubuntu6.2
Candidate: 0.8.8-1ubuntu6.2
Version table:
*** 0.8.8-1ubuntu6.2 0
500 http://apt.sonosite.com/ubuntu/ natty-updates/main amd64 Packages
500 http://apt.sonosite.com/ubuntu/ natty-security/main amd64 Packages
100 /var/lib/dpkg/status
0.8.8-1ubuntu6 0
500 http://apt.sonosite.com/ubuntu/ natty/main amd64 Packages
qemu-img version 0.14.0
# vboxmanage -v
4.0.12r72916
REPRODUCTION STEPS (requires Windows 7 or Windows 2008 R2 with < 1GB of free
space)
## WINDOWS MACHINE ##
Use Computer Management > Disk Management
-Create 2 VHD files, both dynamically expanding 120GB and 140GB respectively.
-Do not initialize or format.
These files will need to be transferred to an Ubuntu KVM machine (pscp
is what I used but usb would work as well).
## UBUNTU KVM MACHINE ##
# ls *.vhd
120g-dyn.vhd 140g-dyn.vhd
# kvm-img info 120g-dyn.vhd
image: 120g-dyn.vhd
file format: vpc
virtual size: 120G (128847052800 bytes)
disk size: 244K
# kvm-img info 140g-dyn.vhd
image: 140g-dyn.vhd
file format: vpc
virtual size: 127G (136899993600 bytes)
disk size: 284K
# kvm-img info 120g-dyn.vhd | grep "virtual size"
virtual size: 120G (128847052800 bytes)
# kvm-img info 140g-dyn.vhd | grep "virtual size"
virtual size: 127G (136899993600 bytes)
Regardless of how big the second vhd is I always get a virtual size of
127G
Now if we use virtualbox to view the vhds we see markedly different
results.
# VBoxManage showhdinfo 120g-dyn.vhd
UUID: e63681e0-ff12-4114-85de-7d13562b36db
Accessible: yes
Logical size: 122880 MBytes
Current size on disk: 0 MBytes
Type: normal (base)
Storage format: VHD
Format variant: dynamic default
Location: /root/120g-dyn.vhd
# VBoxManage showhdinfo 140g-dyn.vhd
UUID: 94531905-46b4-469f-bb44-7a7d388fb38f
Accessible: yes
Logical size: 143360 MBytes
Current size on disk: 0 MBytes
Type: normal (base)
Storage format: VHD
Format variant: dynamic default
Location: /root/140g-dyn.vhd
# kvm-img convert -f vpc -O raw 120g-dyn.vhd 120g-dyn.img
#
# kvm-img convert -f vpc -O raw 140g-dyn.vhd 140g-dyn.img
#
# kvm-img info 120g-dyn.img
image: 120g-dyn.img
file format: raw
virtual size: 120G (128847052800 bytes)
disk size: 0
# kvm-img info 120g-dyn.img | grep "virtual size"
virtual size: 120G (128847052800 bytes)
# kvm-img info 140g-dyn.img
image: 140g-dyn.img
file format: raw
virtual size: 127G (136899993600 bytes)
disk size: 0
# kvm-img info 140g-dyn.img | grep "virtual size"
virtual size: 127G (136899993600 bytes)
Notice after the conversion the raw image will the taken on the
partial geometry of the vhd, thus rendering that image invalid.
vboxmanage has a clonehd option which allows you to successfully
convert vhd to a raw image, which kvm then sees properly.
For giggles I also tested with a 140GB fixed VHD (in the same manner
as above) and it displayed the virtual size as correct, so a good work
around is to convert your VHDs to fixed, then use kvm-img to convert
them.
Keep in mind that these reproduction steps will not have a file
systems therefore no valid data, if there were for example NTFS with a
text file the problem would still occur but more importantly the guest
trying to use it would not be able to open the disk because of it
being unable to find the final sector.
So long story short I think we are dealing with 2 issues here.
1) kvm not being able to deal with dynamic VHD files larger than 127GB
2) kvm-img not generating an error when it "fails" at converting or
displaying information on dynamic VHDs larger than 127GB. The error should be
something like "qemu-kvm does not support dynamic VHD files larger that
127GB..."
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