On Thu, Apr 14, 2022 at 16:36:38 +0000, Bjoern Teipel wrote: > Hello everyone, Hi, > > 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. Hmm, this is really weird if the difference is in the guest-facing device frontend. Since libvirt is merely setting up the block job for the copy and the copy itself is handled by qemu I suggest you contact the qemu-block@xxxxxxxxxx mailing list. Unfortunately you didn't provide any information on the disk configuration (the VM XML) or how you start the blockjob, which I could translate for you into qemu specifics. If you provide such information I can do that to ensure that the qemu folks have all the relevant information.