[Qemu-devel] qmp block-mirror hang, lots of nfs op/s on nfs source disk

[Alexandre DERUMIER]

Hi,

I'm currently playing with drive-mirror, (qemu 2.2)

and I have qmp hang when drive-mirror is starting.

just after qmp "drive-mirror" exec, qmp socket or hmp are not responding.

After some times it's working again, and I can see result of query-block-jobs.


The source volume is on nfs (v4), and it seem that the bigger the volume is, 
the bigger I need to wait before the mirror begin.


Looking at nfsiostat

   op/s         rpc bklog
1806.00            0.00
read:             ops/s            kB/s           kB/op         retrans         
avg RTT (ms)    avg exe (ms)
                  0.000           0.000           0.000        0 (0.0%)         
  0.000           0.000
write:            ops/s            kB/s           kB/op         retrans         
avg RTT (ms)    avg exe (ms)
                  0.000           0.000           0.000        0 (0.0%)         
  0.000           0.000


I'm seeing a lot of  nfs op/s on source disk (but not read).

I wonder if some kind of source file scan is done ? is it expected ?

I can reproduce it 100%

I found a report on redhat bugzilla here, which seem to have same behaviour 
(not on nfs):
https://bugzilla.redhat.com/show_bug.cgi?id=1185172