Dear Sir,
    I use dirty bitmap to backup kvm raw images. I did not shutdown or suspend the vm when backup. 
    I try to export backup as raw images or qcow2 images  when doing full backups as the origin disk is in raw format, all backup jobs finish successfully. But only the raw images  works, the guest os runs well. The qcow2 backup has data corruption and the guest os is in rescue mode.This happens all the time and no operation is done to the vm when doing backup.

export as raw disk
{ "type": "drive-backup", "data": {"device": "drive-virtio-disk0", "target": "/datastore/centos.raw","sync":"full" ,"format": "raw"}}
export as qcow2 disk
{ "type": "drive-backup", "data": {"device": "drive-virtio-disk0", "target": "/datastore/centos.raw","sync":"full" ,"format": "qcow2"}}

After I suspend the vm, and export qcow2 disk, the disk works.
Are there any limits when using bitmap to backup raw disks? For example , we should keep the backup disk in the same format as the origin when vm is running?