On 19.11.2014 12:41, Paolo Bonzini wrote:
On 19/11/2014 12:39, Prof. Dr. Michael Schefczyk wrote:
Dear Paolo,
thank you very much for your prompt reply.
Hi,
please keep the replies on the mailing list. I've added the qemu-devel
mailing list, where more people should be able to see the message and
hopefully reply with something helpful.
Also, how do you do the backups?
Paolo
For example, I have a guest named "gatewayb72.img" where the backup failed. If
I thereafter try to create or delete a snapshot, the following reply occurs on the
command line:
[root@linuxhost2 kvm02]# qemu-img snapshot -d gatewayb72 /kvm02/gatewayb72.img
qemu-img: Could not open '/kvm02/gatewayb72.img': Could not read snapshots:
File too large
If I want to reboot that machine, I get the following error:
Fehler beim Starten der Domain: Interner Fehler: Prozess wurde während der
Verbindungsaufnahme zum Monitor beendet : qemu-kvm: -drive
file=/kvm02/gatewayb72.img,if=none,id=drive-virtio-disk0,format=qcow2,cache=none:
could not open disk image /kvm02/gatewayb72.img: Could not read snapshots:
File too large
Traceback (most recent call last):
File "/usr/share/virt-manager/virtManager/asyncjob.py", line 100, in
cb_wrapper
callback(asyncjob, *args, **kwargs)
File "/usr/share/virt-manager/virtManager/asyncjob.py", line 122, in tmpcb
callback(*args, **kwargs)
File "/usr/share/virt-manager/virtManager/domain.py", line 1220, in startup
self._backend.create()
File "/usr/lib64/python2.7/site-packages/libvirt.py", line 698, in create
if ret == -1: raise libvirtError ('virDomainCreate() failed', dom=self)
libvirtError: Interner Fehler: Prozess wurde während der Verbindungsaufnahme
zum Monitor beendet : qemu-kvm: -drive
file=/kvm02/gatewayb72.img,if=none,id=drive-virtio-disk0,format=qcow2,cache=none:
could not open disk image /kvm02/gatewayb72.img: Could not read snapshots:
File too large
Based on the facts I can see, the file is not too large. When reading the first error,
the file size was 13.8 GB, while the limit is 14.5 GB. The same does also happen with
files which are only, for example 6 GB big, while their limit is also 14.5 GB. Therefore,
I think that the "file too large" really stands for something else.
It most probably does, yes. Some months ago, we included a limit in
qemu's qcow2 implementation for the (internal) snapshot table size. When
this limit is hit, "File too large" will be printed (it's a pretty bad
error message, I know, but we thought it never to occur for reasonable
images, so we did not see the need to improve it). That limit is 64 MB,
which comes from having 1 kB of metadata per snapshot in average and a
maximum of 64k snapshots. 1 kB per snapshot is reasonable: Normally, you
have 56 bytes plus the length of the snapshot's name plus the length of
the snapshot's ID (plus a couple of bytes of padding).
We have indeed seen some bug reports regarding this limit; however,
nobody could provide us with an image to look into this issue so far (as
far as I'm aware), and we could not reproduce it ourselves.
I understand that providing a 13.8 GB image is a bit much, but maybe you
are able to do it anyway (the TU Dresden does have a reasonable internet
connection, as far as I'm aware) or, if possible, provide us with
information on how to recreate a similar image ourselves.
Max
