This is an automated cleanup. This bug report has been moved to QEMU's new bug tracker on gitlab.com and thus gets marked as 'expired' now. Please continue with the discussion here:
https://gitlab.com/qemu-project/qemu/-/issues/307 ** Changed in: qemu Status: New => Expired ** Bug watch added: gitlab.com/qemu-project/qemu/-/issues #307 https://gitlab.com/qemu-project/qemu/-/issues/307 -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1912224 Title: qemu may freeze during drive-mirroring on fragmented FS Status in QEMU: Expired Bug description: We have odd behavior in operation where qemu freeze during long seconds, We started an thread about that issue here: https://lists.gnu.org/archive/html/qemu-devel/2020-11/msg05623.html It happens at least during openstack nova snapshot (qemu blockdev-mirror) or live block migration(which include network copy of disk). After further troubleshoots, it seems related to FS fragmentation on host. reproducible at least on: Ubuntu 18.04.3/4.18.0-25-generic/qemu-4.0 Ubuntu 16.04.6/5.10.6/qemu-5.2.0-rc2 # Lets create a dedicated file system on a SSD/Nvme 60GB disk in my case: $sudo mkfs.ext4 /dev/sda3 $sudo mount /dev/sda3 /mnt $df -h /mnt Filesystem Size Used Avail Use% Mounted on /dev/sda3 59G 53M 56G 1% /mnt #Create a fragmented disk on it using 2MB Chunks (about 30min): $sudo python3 create_fragged_disk.py /mnt 2 Filling up FS by Creating chunks files in: /mnt/chunks We are probably full as expected!!: [Errno 28] No space left on device Creating fragged disk file: /mnt/disk $ls -lhs 59G -rw-r--r-- 1 root root 59G Jan 15 14:08 /mnt/disk $ sudo e4defrag -c /mnt/disk Total/best extents 41971/30 Average size per extent 1466 KB Fragmentation score 2 [0-30 no problem: 31-55 a little bit fragmented: 56- needs defrag] This file (/mnt/disk) does not need defragmentation. Done. # the tool^^^ says it is not enough fragmented to be able to defrag. #Inject an image on fragmented disk sudo chown ubuntu /mnt/disk wget https://cloud-images.ubuntu.com/bionic/current/bionic-server-cloudimg-amd64.img qemu-img convert -O raw bionic-server-cloudimg-amd64.img \ bionic-server-cloudimg-amd64.img.raw dd conv=notrunc iflag=fullblock if=bionic-server-cloudimg-amd64.img.raw \ of=/mnt/disk bs=1M virt-customize -a /mnt/disk --root-password password:xxxx # logon run console activity ex: ping -i 0.3 127.0.0.1 $qemu-system-x86_64 -m 2G -enable-kvm -nographic \ -chardev socket,id=test,path=/tmp/qmp-monitor,server,nowait \ -mon chardev=test,mode=control \ -drive file=/mnt/disk,format=raw,if=none,id=drive-virtio-disk0,cache=none,discard\ -device virtio-blk-pci,scsi=off,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1,write-cache=on $sync $echo 3 | sudo tee -a /proc/sys/vm/drop_caches #start drive-mirror via qmp on another SSD/nvme partition nc -U /tmp/qmp-monitor {"execute":"qmp_capabilities"} {"execute":"drive-mirror","arguments":{"device":"drive-virtio-disk0","target":"/home/ubuntu/mirror","sync":"full","format":"qcow2"}} ^^^ qemu console may start to freeze at this step. NOTE: - smaller chunk sz and bigger disk size the worst it is. In operation we also have issue on 400GB disk size with average 13MB/extent - Reproducible also on xfs Expected behavior: ------------------- QEMU should remain steady, eventually only have decrease storage Performance or mirroring, because of fragmented fs. Observed behavior: ------------------- Perf of mirroring is still quite good even on fragmented FS, but it breaks qemu. ###################### create_fragged_disk.py ############ import sys import os import tempfile import glob import errno MNT_DIR = sys.argv[1] CHUNK_SZ_MB = int(sys.argv[2]) CHUNKS_DIR = MNT_DIR + '/chunks' DISK_FILE = MNT_DIR + '/disk' if not os.path.exists(CHUNKS_DIR): os.makedirs(CHUNKS_DIR) with open("/dev/urandom", "rb") as f_rand: mb_rand=f_rand.read(1024 * 1024) print("Filling up FS by Creating chunks files in: ",CHUNKS_DIR) try: while True: tp = tempfile.NamedTemporaryFile(dir=CHUNKS_DIR,delete=False) for x in range(CHUNK_SZ_MB): tp.write(mb_rand) os.fsync(tp) tp.close() except Exception as ex: print("We are probably full as expected!!: ",ex) chunks = glob.glob(CHUNKS_DIR + '/*') print("Creating fragged disk file: ",DISK_FILE) with open(DISK_FILE, "w+b") as f_disk: for chunk in chunks: try: os.unlink(chunk) for x in range(CHUNK_SZ_MB): f_disk.write(mb_rand) os.fsync(f_disk) except IOError as ex: if ex.errno != errno.ENOSPC: raise ###########################################################3 To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1912224/+subscriptions
