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Any size limitation on the backing store?
by Jeff Brown 10 May '22

10 May '22

We have a few QCOW2 images that have grown rather large (> 250GB) and to back them up across the VLAN is resource intensive and time consuming. What I'd like to do to optimise backups is freeze the backing store and always run the VMs in 'snapshot 1', and then run 'snapshot 2' to backup 'snapshot 1' to reciprocal failover hypervisors in the DC. I do know it's common practice to even run multiple VMs off a single "golden image" backing store, but I'm concerned about the performance impact with such a large backing store, and 'snapshot 1' growing at ~10GB a year. With that in mind, it should be feasible to pivot 'snapshot 1' into the backing image periodically. Further, I am aware of incremental backups which Debian 11 doesn't yet support. I think it's coming in Debian 12, but some of our servers are actually still on Debian 10. jeff@abacus:/var/lib/libvirt/images$ virsh backup-begin dev error: Operation not supported: incremental backup is not supported yet In a nutshell, is it feasible to run off an > 250GB and growing backing store? Thanks in advance for any advice. -- Jeff Brown Future Foundation Cell 074 101 5170 VoIP 087 550 1210 Fax: 086 532 3508

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virtqemud high CPU load
by lejeczek 06 May '22

06 May '22

Hi guys, Anybody on centos9? With latest updates I get 100% load (so one core fully loaded) almost all the time, I don't remember that being the case before. 'virtqemud' itself does not log much, with default verbosity. Any thoughts? many thanks, L.

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Issue with Guest and 2 Displays
by Thomas Luening 29 Apr '22

29 Apr '22

Hi @ all Since switching from Debian 10 to Debian 11, I've had a new small unsolved problem... with essentially the same customizing as before. It all takes place on my local Desktop-PC, where I have set up a restricted VM for actions in the internet. After I started the VM locally on my PC, I can operate the VM with the virtviewer without any errors. If I then open the second monitor via the Menu 'View->Display', a blank white window appears with the message "Waiting for display 2". xrandr correctly shows the second display as disconnected and also all available display-modes. After the following command xrandr --output Virtual-2 --auto --right-of Virtual-1 both (!) displays are white and both are waiting for a display.... and nothing works anymore. A previously started SSH connection to the VM from the PC shows the following for this moment: tom@pc:~ $ ssh 192.168.100.10 $ tom@vm:~ $su- Password: root@vm:~ # journalctl -f Apr 29 16:24:34 internet kernel: [drm] driver is in bug mode Apr 29 16:24:44 internet spice-vdagent[809]: Unable to find a display id for output index 2) Apr 29 16:24:44 internet spice-vdagent[809]: Unable to find a display id for output index 3) Apr 29 16:24:44 internet spice-vdagent[809]: Unable to find a display id for output index 2) Apr 29 16:24:44 internet spice-vdagent[809]: Unable to find a display id for output index 3) Apr 29 16:24:44 internet kernel: input: spice vdagent tablet as /devices/virtual/input/input7 It is no longer possible to restart the VM via "systemctl reboot", the VM is probably stuck in some systemd-timeouts, only "systemctl reboot -ff" leads to a reboot as a hard intervention. Does anyone know this problem? Is there a solution for this, to get the second display working? Below some relevant system-informations of my PC and the VM. root@pc:~ $ lsb_release -a Distributor ID: Debian Description: Debian GNU/Linux 11 (bullseye) Release: 11 Codename: bullseye root@pc:~ # uname -a Linux pc 5.10.0-13-amd64 #1 SMP Debian 5.10.106-1 (2022-03-17) x86_64 GNU/Linux root@pc:~ # cat /etc/libvirt/qemu/internet.xml | grep '<video' -A 3 <video> <model type='qxl' ram='65536' vram='65536' vgamem='16384' heads='2' primary='yes'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/> </video> tom@vm:~ $ lsb_release -a Distributor ID: Debian Description: Debian GNU/Linux 11 (bullseye) Release: 11 Codename: bullseye tom@vm:~ $ dpkg -l | grep -i spice ii spice-vdagent 0.20.0-2 amd64 Spice agent for Linux tom@vm:~ $ systemctl status spice-vdagent.service ● spice-vdagentd.service - Agent daemon for Spice guests Loaded: loaded (/lib/systemd/system/spice-vdagentd.service; indirect; vendor preset: enabled) Active: active (running) since Fri 2022-04-29 16:00:56 CEST; 16min ago TriggeredBy: ● spice-vdagentd.socket Process: 847 ExecStart=/usr/sbin/spice-vdagentd $SPICE_VDAGENTD_EXTRA_ARGS (code=exited, status=0/SUCCESS) Main PID: 849 (spice-vdagentd) Tasks: 2 (limit: 4702) Memory: 944.0K CPU: 1.918s CGroup: /system.slice/spice-vdagentd.service └─849 /usr/sbin/spice-vdagentd Thanks and Best Regards Tom

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Re: how to change emulator path during live migration
by Peter Krempa 27 Apr '22

27 Apr '22

[re-adding libvirt-users list] Please always reply to the list so that the follow-up conversation is archived and delivered to all subscribers. On Wed, Apr 27, 2022 at 15:36:54 +0800, Jiatong Shen wrote: > Thank you for the feedback! > > Is it ok if the source node does not contain a emulator path used by the > dest node? for example, on src emulator path is /a/b/c, but > on dest it is /a/b/d, and /a/b/d does not exist on src. You can change the emulator path arbitrarily. The only limitation is that the emulator you pick (the binary, not the path) must be able to run the VM, but that will be validated during the migration.

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how to change emulator path during live migration
by Jiatong Shen 27 Apr '22

27 Apr '22

Hello libvirt experts, I am facing the following exceptions during live migrating a virtual machine from one compute node to another. file or directory: libvirt.libvirtError: Cannot check QEMU binary /usr/bin/kvm-spice: No such file or directory File "/var/lib/openstack/lib/python3.6/site-packages/eventlet/tpool.py", line 83, in tworker rv = meth(*args, **kwargs) File "/var/lib/openstack/lib/python3.6/site-packages/libvirt.py", line 1745, in migrateToURI3 if ret == -1: raise libvirtError ('virDomainMigrateToURI3() failed', dom=self) libvirt.libvirtError: Cannot check QEMU binary /usr/bin/kvm-spice: No such file or directory After some investigation, we found that this error is triggered because we do not have qemu-kvm installed in our container, btw the libvirt is directly installed on the source node. I have following questions Is it possible to change emulator during live migration? I try to to remove emulator under devices but looks like it does not help. thank you very much and looking forward for the feedback. -- Best Regards, Jiatong Shen

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set fixed time at vm guest startup?
by Fred Clift 26 Apr '22

26 Apr '22

I'm looking at the <clock> libvirt parameters. Is there a way to set the guests clock to a specific time/date at virt startup? I'm trying to virtualize a system with pci passthrough for a hardware device that wants to always live in pre-2011. The license manager for the software/hardware has 31-bit overflow of time calculations. The current process on the physical machine is to power it on, use the bios to set the hardware date to Jan 1 2010, boot the system, use an RC script to ntp-set the date now that the hardware is up and running, and then everything works till next boot. We even have a nice rc script that will set the clock back to 2010 if you do a clean shutdown/reboot. I see I can set my clock sync to variable and specify a negative offset - is there a way to just say "always be jan 10 2010 when you power on"? Fred

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discard option on ext4 mounts in QEMU qcow2 images
by Nate Collins 26 Apr '22

26 Apr '22

Hello, Does anyone have any real-world statistics on the reliability and performance of the ext4 discard option in QEMU VMs? I've heard it's discouraged for physical devices, as some are inefficient in how TRIM requests are processed, but I was wondering if there were any drawbacks/warnings when it comes to virtual disks (in this case, QCOW2s). I currently use either virtio-scsi or virtio-blk drivers for disk images depending on what the host/guest support, and run TRIMs weekly, but having an immediate freeing of space is desirable for many reasons. Also wondering if snapshots on snapshotting filesystems (such as ZFS) can run into corruption or other issues if snapshots are taken during a TRIM. Thanks.

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race condition? virsh migrate --copy-storage-all
by Valentijn Sessink 20 Apr '22

20 Apr '22

Hi list, I'm trying to migrate a few qemu virtual machines between two 1G ethernet connected hosts, with local storage only. I got endless "error: operation failed: migration of disk vda failed: Input/output error" errors and thought: something wrong with settings. However, then, suddenly: I succeeded without changing anything. And, hey: while ! time virsh migrate --live --persistent --undefinesource --copy-storage-all ubuntu20.04 qemu+ssh://duikboot/system; do a=$(( $a + 1 )); echo $a; done ... retried 8 times, but then: success. This smells like a race condition, doesn't it? A bit weird is the fact that the migration seems to succeed every time while copying from revolving disks to SSD; but the other way around has this Input/output error. There are some messages in /var/log/syslog, but not at the time of the failure, and no disk errors. These disks are LVM2 volumes and they live on raid arrays - and/so there is not a real, as in physical, I/O-error. Source system has SSD's, target system has regular disks. 1) is this the right mailing list? I'm not 100% sure. 2) how can I research this further? Spending hours on a "while / then" loop to try and retry live migration looks like a dull job for my poor computers ;-) Best regards, Valentijn

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Virtio-scsi and block mirroring
by Bjoern Teipel 20 Apr '22

20 Apr '22

Hello everyone, I’m looking at an issue where I do see guests freezing (Dl) process state during a block disk mirror from one storage to another storage (NFS) where the network stack of the guest can freeze for up to 10 seconds. Looking at the storage and IO I noticed good throughput ad low latency <3ms and I am having trouble to track down the source for the issue, as neither storage nor networking show issues. Interestingly when I do the same test with virtio-blk I do not really see the process freezes at the frequency or duration compared to virtio-scsi which seem to indicate a client side rather than storage side problem. I had looked at the syscalls and nothing stuck out: % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 28.51 20.672654 8339 2479 ioctl 27.81 20.162714 3379 5967 31 futex 22.02 15.964498 785 20335 poll 15.22 11.038403 150 73561 io_submit 4.17 3.023285 41 73540 lseek 1.20 0.868003 5 158591 write 0.63 0.459030 11 42871 ppoll 0.22 0.159263 8 19314 recvmsg 0.16 0.115520 5 22526 read 0.04 0.029149 29149 1 restart_syscall 0.01 0.009252 28 330 sendmsg 0.00 0.001221 1221 1 munmap 0.00 0.000458 22 21 fcntl 0.00 0.000286 95 3 openat 0.00 0.000166 5 32 rt_sigprocmask 0.00 0.000103 10 10 fdatasync 0.00 0.000099 25 4 clone 0.00 0.000081 7 12 mmap 0.00 0.000077 19 4 close 0.00 0.000076 6 12 mprotect 0.00 0.000056 14 4 madvise 0.00 0.000025 6 4 set_robust_list 0.00 0.000023 6 4 prctl ------ ----------- ----------- --------- --------- ---------------- 100.00 72.504442 419626 31 total Does anyone have an idea how to better debug this issue ? Thanks Bjoern

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When does the balloon-change or control-error event occur
by Han Han 19 Apr '22

19 Apr '22

Hi developers, I have questions about balloon-change or control-error event: 1. What's the meaning of these events 2. When do the events occur? The comments of their callbacks don't mention that( https://gitlab.com/libvirt/libvirt/-/blob/master/include/libvirt/libvirt-do… https://gitlab.com/libvirt/libvirt/-/blob/master/include/libvirt/libvirt-do… )

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