Hi Eric and list,
I had another production VM start pausing itself. This one had
been running for more than 4 years on a 60G LVM volume. It has
had the occasional snapshot during that time though all have been
"removed" using the virt-manager gui so I used qemu-img as you
suggested.
# qemu-img convert /dev/trk-kvm-02-vg/rt44 -O qcow2
/mnt/scratch/rt44.qcow2
dd'd the qcow2 image back on to the LV after testing it boots OK
directly from the image and it is in production again.
The VM itself reports ample space available:
$ df -h
Filesystem Size Used Avail Use%
Mounted on
udev 3.9G 0 3.9G 0%
/dev
tmpfs 789M 8.8M 780M 2%
/run
/dev/mapper/RT--vg-root 51G 21G 28G 42% /
tmpfs 3.9G 0 3.9G 0%
/dev/shm
tmpfs 5.0M 0 5.0M 0%
/run/lock
tmpfs 3.9G 0 3.9G 0%
/sys/fs/cgroup
/dev/vda1 472M 155M 293M 35%
/boot
192.168.0.16:/volume1/fileLevel 8.1T 2.5T 5.6T 31%
/mnt/nfs/fileLevel
tmpfs 789M 0 789M 0%
/run/user/1000
I would prefer to not get caught out again with this machine
pausing, how can I determine how much space is being used up by
'deleted' internal snapshots? Do you have any suggested reading
on this?
If I extend the LVM volume but not the guest file system will
snapshots be "at the end" of the LV and "outside" the guest file
system?
If I were to expand the guest's ext4 file system I would want to
do it unmounted and from a live CD but I'm having a heck of a time
getting my live distro to use the virtio disk drivers. Any advice
there?
sincerely
On 2018-05-01 02:31 PM, Eric Blake
wrote:
On
05/01/2018 04:17 PM, Paul O'Rorke wrote:
I have been using internal snapshots on
production qcow2 images for a couple of years, admittedly as
infrequently as possible with one exception and that exception
has had multiple snapshots taken and removed using
virt-manager's GUI.
I was unaware of this:
There are some technical downsides to
internal snapshots IIUC, such as inability to free the space
used by the
internal snapshot when it is deleted,
This is not an insurmountable difficulty, just one that no one has
spent time coding up.
This might explain why this VM recently kept going into a paused
state and I had to extend the volume to get it to stay up. This
VM is used for testing our software in SharePoint and we make
heavy use of snapshots. Is there nothing I can to do recover
that space?
If you have no internal snapshots, you can do a 'qemu-img convert'
to copy just the portion of the image that is actively in use; the
copy will use less disk space than the original because it got rid
of the now-unused space. 'virt-sparsify' from libguestfs takes
this one step further, by also removing unused space within the
guest filesystem itself.
In fact, even if you do have internal snapshots, there is probably
a sequence of 'qemu-img convert' invocations that can ultimately
convert all of your internal snapshots into an external chain of
snapshots; but I don't have a ready formula off-hand to point to
(experiment on an image you don't care about, before doing it on
your production image).
What would be the best practice then for a
VM that needs to be able to create and remove snapshots on a
regular basis?
In a managed environment, external snapshots probably have the
most support for creating and later merging portions of a chain of
snapshots, although we could still improve libvirt to make this
feel like more of a first class citizen.
