[Users] Info on snapshot removal operations and final disk format

[Gianluca Cecchi]

Hello,
I'm on oVirt 3.2.3-1 on a Fedora 18 all-in-one test server.
I have a Windows XP VM that has a disk in qcow2 format and has a snapshot on it.
When I delete the snapshot I see, from the commands intercepted, that
the final effect is to have a raw disk (aka preallocated) .... is this
correct and always true?

Does this mean that even if I create a VM with thin provisioned disks,
as soon as I take at least one snapshot and I then delete it I only
have raw disks?
Or am I missing anything?

This what I observed:
as soon as I launch delete snapshot operation:

raw format of new disk
vdsm     30805  1732  6 13:24 ?        00:00:00 /usr/bin/dd
if=/dev/zero of=/rhev/data-center/65c9777e-23f1-4f04-8cea-e7c8871dc88b/0a8035e6-e41d-40ff-a154-e0a374f264b2/images/75c54716-5222-4ad6-91f2-8b312eacc4b4/d4fa7785-8a89-4d13-9082-52556ab0b326_MERGE
bs=1048576 seek=0 skip=0 conv=notrunc count=11264 oflag=direct

after about 5 minutes:
convert from qemu format to raw format
vdsm     31287  1732  7 13:29 ?        00:00:08 /usr/bin/qemu-img
convert -t none -f qcow2
/rhev/data-center/65c9777e-23f1-4f04-8cea-e7c8871dc88b/0a8035e6-e41d-40ff-a154-e0a374f264b2/images/75c54716-5222-4ad6-91f2-8b312eacc4b4/d4fa7785-8a89-4d13-9082-52556ab0b326
-O raw /rhev/data-center/65c9777e-23f1-4f04-8cea-e7c8871dc88b/0a8035e6-e41d-40ff-a154-e0a374f264b2/images/75c54716-5222-4ad6-91f2-8b312eacc4b4/d4fa7785-8a89-4d13-9082-52556ab0b326_MERGE

at the end probably there is a rename of the disk file and
qemu-img info /rhev/data-center/65c9777e-23f1-4f04-8cea-e7c8871dc88b/0a8035e6-e41d-40ff-a154-e0a374f264b2/images/75c54716-5222-4ad6-91f2-8b312eacc4b4/d4fa7785-8a89-4d13-9082-52556ab0b326

image: /rhev/data-center/65c9777e-23f1-4f04-8cea-e7c8871dc88b/0a8035e6-e41d-40ff-a154-e0a374f264b2/images/75c54716-5222-4ad6-91f2-8b312eacc4b4/d4fa7785-8a89-4d13-9082-52556ab0b326
file format: raw
virtual size: 11G (11811160064 bytes)
disk size: 9.5G


# ll /rhev/data-center/65c9777e-23f1-4f04-8cea-e7c8871dc88b/0a8035e6-e41d-40ff-a154-e0a374f264b2/images/75c54716-5222-4ad6-91f2-8b312eacc4b4/
total 9995476
-rw-rw----. 1 vdsm kvm     1048576 Nov 16 12:09
6ac73ee2-6419-43a4-91e7-7d4ef2026943_MERGE.lease
-rw-rw----. 1 vdsm kvm 11811160064 Nov 16 13:32
d4fa7785-8a89-4d13-9082-52556ab0b326
-rw-rw----. 1 vdsm kvm     1048576 Mar 23  2013
d4fa7785-8a89-4d13-9082-52556ab0b326.lease
-rw-rw----. 1 vdsm kvm     1048576 Nov 16 13:29
d4fa7785-8a89-4d13-9082-52556ab0b326_MERGE.lease
-rw-r--r--. 1 vdsm kvm         274 Nov 16 13:29
d4fa7785-8a89-4d13-9082-52556ab0b326.meta

Thanks
Gianluca