On Mon, 06/23 10:06, lihuiba wrote: > Hi, all > > > I'm using a qcow2 image stored on a SSD RAID1 (2 x intel S3500), and I'm > benchmarking the > system using fio. Although the throughput in VM (with KVM and virtio enabled) > is acceptable (67% > of thoughtput in host), the IOPS performance seems is extremely low ---- only > 2% of IOPS in host. > > > I was initially using qemu-1.1.2, and I also tried qemu-1.7.1 for comparison. > There was no significant > difference. > > > In contrast, raw image and LVM perform very well. They usually achieve 90%+ > of throughput and > 60%+ of IOPS. So the problem must lie in the QCOW2 image format. > > > And I observed that, when I perform 4KB IOPS benchmark in VM with a QCOW2 > image, fio in VM reports > it is reading 9.x MB/s, while iostat in host reports the SSD is being read > 150+ MB/s. So QEMU or QCOW2 > must have amplified the amount of read by nearly 16 times. > > > So, how can I fix or tune the performance issue of qcow2?
Did you prefill the image? Amplification could come from cluster allocation. Fam > > > Thanks! > > > > > PS: > 1. qemu parameters: > -enable-kvm -cpu qemu64 -rtc base=utc,clock=host,driftfix=none -usb -device > usb-tablet -nodefaults -nodefconfig -no-kvm-pit-reinjection -global > kvm-pit.lost_tick_policy=discard -machine pc,accel=kvm -vga std -k en-us -smp > 8 -m 4096 -boot order=cdn -vnc :1 -drive > file=$1,if=none,id=drive_0,cache=none,aio=native -device > virtio-blk-pci,drive=drive_0,bus=pci.0,addr=0x5 -drive > file=$2,if=none,id=drive_2,cache=none,aio=native -device > virtio-blk-pci,drive=drive_2,bus=pci.0,addr=0x7 > > > 2. fio parameters for IOPS: > fio --filename=/dev/vdb --direct=1 --ioengine=libaio --iodepth 32 --thread > --numjobs=1 --rw=randread --bs=4k --size=100% --runtime=60s --group_reporting > --name=test > > > 3. fio parameters for throughput: > fio --filename=/dev/vdb--direct=1 --ioengine=psync --thread --numjobs=3 > --rw=randread --bs=1024k --size=100% --runtime=60s --name=randread > --group_reporting -name=test > > >
