Using blockdev-mirror for Live Backup

[aliqrudi]

Hi,

We are executing hundreds of VMs in our hosts (dual AMD EPYC 7002 CPUs
+ 2TB memory + 8 NVMe disks).  To cope with disk failures, we tried
different Linux software RAID mechanisms.  At high disk usage, all of
them faced unexpectedly high CPU load, mostly in the kernel.  Therefore
we decided not to use software RAID.

As an alternative, can we use blockdev-mirror for keeping a live
mirror of each image?  The problem seems to be that when Qemu starts
and the mirror exists, it does not need to write the whole disk to the
mirror again; writing just the updates would be enough.  Looking at
the code, the incremental sync mode (which probably does what is
needed) is not supported.

Is using blockdev-mirror a good idea?

Is there any reason that blockdev-mirror's incremental sync mode is
missing?

As the mirror device is updated in Qemu itself, does using virtio
devices help?

Thank you very much for your time.

Best wishes,
Ali