[PVE-User] Problem with sparse files disks

Fabien Bagard fabien.bagard at intersec.com
Fri Apr 23 11:58:41 CEST 2010

Hi all!

First of all, thank you for this wonderful enterprise-class suite !

I use PVE since 2 weeks from now, and I encountered some problems


All my VMs uses sparse files as disks (raw format). I wanted to migrate 
all my VMs from a server to another (same characteristics, same disk 
space, ...) After a while, I got an error, no space left on device. I 
checked VM disks size with du -sm. The surprise was : On the master, a 
50Go disk reported a size of 1Go (normal, it's a sparse file), but once 
migrated, it reported a size of 50Go... Maybe you should consider using 
the '-S' option of rsync (handling sparse files). But I don't know what 
is the effect of -S option on a non-sparse file.

For those who are stuck with non-sparse files after a migration, it is 
possible to recreate them, without any loss of data :

bender:/var/lib/vz/images/100# du -sm vm-100-disk-1.raw
51251    vm-100-disk-1.raw

Convert the big disk in another format, for example qcow2 : qemu-img 
convert -f raw -O qcow2 vm-100-disk-1.raw vm-100-disk-1.qcow2

bender:/var/lib/vz/images/100# du -sm vm-100-disk-1.qcow2
890    vm-100-disk-1.qcow2

then convert it back to raw format : qemu-img convert -f qcow2 -O raw 
vm-100-disk-1.qcow2 vm-100-disk-1.raw

bender:/var/lib/vz/images/100# du -sm vm-100-disk-1.raw
828    vm-100-disk-1.raw

By the way, we can see that raw format is lighter than qcow2 ;)


Thank you again for you wonderful job ! PVE is exactly what I needed !

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