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[Qemu-devel] [Bug 1120383] Re: incremental live block migration of qemu


From: Reno Gan
Subject: [Qemu-devel] [Bug 1120383] Re: incremental live block migration of qemu 1.3.1 doesn't work
Date: Sun, 10 Feb 2013 06:37:18 -0000

If you want to reproduce it, you can refer to my test case in this bug 
description, only differences are:
  1) make sure "os.img" is big enough, for example, > 300M
  2) write a script to migrate it in a loop:
       a) migrate from A to B
       b) shutdown guest on B and start it again
       c) check if guest os is healthy. (I use guestfs to do this, you can use 
ssh to write a simple file in the guest file system)

If error happens, the guest os will be mounted as read-only and a lot of
root file system errors will be thrown out in syslog.

I checked the image size from A to B and noticed that image size is
shrinked dramatically. For example, if source size is 300M, only 10M is
left on host B after migration.

I also print out values of "block_mig_state.submitted",
"block_mig_state.read_done", and "block_mig_state.transferred", and
found that if error happened, "submitted" is zero and "read_done" is not
zero.

For example, if 52 blocks are to be migrated from A to B, when migration is 
completed, the three values will be:
     submitted = 0,  read_done = 40,  transferred = 12

That is : a lot of data are actually "readed" but not "transferred",
only part of data are migrated.

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https://bugs.launchpad.net/bugs/1120383

Title:
  incremental live block migration of qemu 1.3.1 doesn't work

Status in QEMU:
  New

Bug description:
  We tested qemu 1.3.1 for live migration of block device. It failed
  with error.   Since qemu-kvm 1.2.0 is ok for this test, we think this
  problem is introduced by new qemu 1.3.x releases.

  To reproduce:

  1. compile qemu 1.3.1:
      # cd qemu-1.3.1
      # ./configure --prefix=/usr --sysconfdir=/etc --target-list=x86_64-softmmu
      # make; make install

  2. prepare source(172.16.1.13):
      # qemu-img create -f qcow2 os.img -b /home/reno/wheezyx64     ###Note: 
wheezyx64 is a template image for Debian Wheezy 
      # qemu-system-x86_64 -hda os.img -m 512 --enable-kvm -vnc :51 -monitor 
stdio

  3. prepare destination(172.16.1.14):
      # qemu-img create -f qcow2 os.img -b /home/reno/wheezyx64    
      # qemu-system-x86_64 -hda os.img -m 512 --enable-kvm -vnc :51 -incoming 
tcp:0:4444

  4. do live migrate:
      on source monitor command prompt, input:
      (qemu) migrate -i tcp:172.16.1.14:4444

  monitor command will quit immediately and on destination host, there are 
errors thrown:
      Receiving block device images
      Co-routine re-entered recursively
      Aborted

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