I have on vm with a disk size of 6TiB. Everytime I need to reboot the host, or change the vm's configuration, the bitmap is dirty causing the next backup task to do a full disk read. This is very slow. It takes 15 hours aprox. to do the whole disk. Not much is being synced to the remote PBS however, because not much data has actually changed.

Is there a way to speed up the backup task? Are my disks just too slow? The VM disk is a "raw" vm disk on a ZFS partition, containing 2 mirrors of 8TB hard drives.