I'm still trying to improve my snapshot behavior. I was reading through the
RedHat documentation and found this, "Important Red Hat recommends the use of
external snapshots” Actually external snapshots sound great. Then on a later
page I found this: “However, external snapshots are currently not fully
implemented on Red Hat Enterprise Linux 7, and are not available when using
virt-manager.” Hrm. Well, that’s for RHEL 7 and I’m using RHEL 8. Maybe it
has been fixed? Apparently no. When I tried to take the external snapshot it
crashed with “libvirt.libvirtError: internal error: unable to execute QEMU
command 'cont': Failed to get shared "write" lock.” It created a new
disk.qcow2, but the memory was not saved. Worse, when I tried to reboot my VM
it was locked to the new disk. I changed it back to my original disk, but it
says it can’t get the lock. Even if it doesn’t work, I didn’t expect taking a
snapshot to be destructive! So, a couple of questions:
1. Is there any way to get external snapshots to work?
2. How do I clear the lock on my disk? There aren’t any VMs alive to be
using it, so I just need to clear the lock.
Below is what I was trying to do:
$ virsh snapshot-create-as centos8_1 externsnap --atomic --diskspec
vda,file=$PWD/disk.qcow2,snapshot=external --memspec
file=$PWD/mem.qcow2,snapshot=external
error: internal error: unable to execute QEMU command 'cont': Failed to get
shared "write" lock
$ ls *.qcow2
disk.qcow2
$ #Noite there is no mem.qcow2
Then when trying to restart I first had to point virt-manager back to my
original VM disk, I got this error about the disk lock:
Error starting domain: internal error: qemu unexpectedly closed the monitor:
2021-09-13T14:12:42.409301Z qemu-kvm: -blockdev
{"node-name":"libvirt-2-format","read-only":false,"driver":"qcow2","file":"libvirt-2-storage","backing":"libvirt-3-format"}:
Failed to get "write" lock
Is another process using the image [/home/leek2/qemu/rhel8_1.qcow2]?
Traceback (most recent call last):
File "/usr/share/virt-manager/virtManager/asyncjob.py", line 75, in cb_wrapper
callback(asyncjob, *args, **kwargs)
File "/usr/share/virt-manager/virtManager/asyncjob.py", line 111, in tmpcb
callback(*args, **kwargs)
File "/usr/share/virt-manager/virtManager/object/libvirtobject.py", line 66,
in newfn
ret = fn(self, *args, **kwargs)
File "/usr/share/virt-manager/virtManager/object/domain.py", line 1280, in
startup
self._backend.create()
File "/usr/lib64/python3.6/site-packages/libvirt.py", line 1234, in create
if ret == -1: raise libvirtError ('virDomainCreate() failed', dom=self)
libvirt.libvirtError: internal error: qemu unexpectedly closed the monitor:
2021-09-13T14:12:42.409301Z qemu-kvm: -blockdev
{"node-name":"libvirt-2-format","read-only":false,"driver":"qcow2","file":"libvirt-2-storage","backing":"libvirt-3-format"}:
Failed to get "write" lock
Is another process using the image [/home/leek2/qemu/rhel8_1.qcow2]?
Thanks,
Jim
