[MooseFS-Users] High disk usage inside vm makes moosefs read only

[<ma...@me...>]

Hi!
I'm using moosefs-3.0.86 on ubuntu 16. This is two node setup. On second
node - node without mfsmaster, only with mfschunkserver, I'm starting
qemu VM (parameters for qemu:  [...] -drive
file=/var/lib/one//datastores/101/42/disk.0,format=qcow2,if=none,id=drive-virtio-disk0,cache=none
-device
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x5,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1,logical_block_size=512,physical_block_size=4096
[...] )

When high I/O starts inside VM then qcow file with vm image becomes
unreadable. OS inside qemu hangs. When I run md5sum on qcow file it also
stuck in D state after reading some part of file.
There is nothing suspicious in syslog. On mfsmaster I have:
> Jan 11 16:57:27 w2t-cl-a-00 mfsmount[15828]: high packet travel time between client and master (0.248819s) - ignoring in time sync
> Jan 11 17:00:00 w2t-cl-a-00 mfsmaster[2501]: no metaloggers connected !!!
> Jan 11 17:00:03 w2t-cl-a-00 mfsmaster[2501]: child finished
> Jan 11 17:00:03 w2t-cl-a-00 mfsmaster[2501]: store process has finished - store time: 3.750

[here, about 17:25 vm stuck in D state]

> Jan 11 17:41:02 w2t-cl-a-00 mfsmaster[2501]: structure check loop


How to fix it? How to debug it?
Thanks,
Marcin