Qemu Migration优化特性 XBZRLE

Qemu Migration优化特性

XBZRLE (Xor Based Zero Run Length Encoding)

概述

用于降低虚拟机downtime和迁移的总时间。尤其对运行内存高负载写的虚拟机有效。
比如SAP的ERP系统这样的大型企业应用。

通过源端cache已经发送的内存页，下次发送该页时就可以对比，只发送变化部分的数据。
因此cache越大，则命中越高。

cache大小可以在迁移前调整。

用法

 1. Verify the destination QEMU version is able to decode the new format.

    {qemu} info migrate_capabilities

    {qemu} xbzrle: off , ...

2. Activate xbzrle on both source and destination:

   {qemu} migrate_set_capability xbzrle on

3. Set the XBZRLE cache size - the cache size is in MBytes and should be a

power of 2. The cache default value is 64MBytes. (on source only)

    {qemu} migrate_set_cache_size 256m

4. Start outgoing migration

    {qemu} migrate -d tcp:destination.host:4444

    {qemu} info migrate

    capabilities: xbzrle: on

    Migration status: active

    transferred ram: A kbytes

    remaining ram: B kbytes

    total ram: C kbytes

    total time: D milliseconds

    duplicate: E pages

    normal: F pages

    normal bytes: G kbytes

    cache size: H bytes

    xbzrle transferred: I kbytes

    xbzrle pages: J pages

    xbzrle cache miss: K

    xbzrle overflow : L