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Live Migration of Virtual Machines

Live Migration of Virtual Machines. Christopher Clark, Keir Fraser, Steven Hand, Jacob Gorm Hanseny , Eric July, Christian Limpach , Ian Pratt, Andrew Wareld. Index . Motivation Migration Pre-copy migration Challenge in Pre-copy Implementation Managed Migration( Xen )

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Live Migration of Virtual Machines

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  1. Live Migration of Virtual Machines Christopher Clark, Keir Fraser, Steven Hand, Jacob GormHanseny, Eric July, Christian Limpach, Ian Pratt, Andrew Wareld

  2. Index • Motivation • Migration • Pre-copy migration • Challenge in Pre-copy • Implementation • Managed Migration(Xen) • Self Migration • Experiment • Optimization

  3. Motivation • Why we need live migration? We want to move VM without interrupting VM service. Products: • Xen 2.0 : live migration • VMware:VMotion

  4. Migration • Two important consideration: 1. Downtime 2. Total migration time • All migrations mechanism can be divided into three phases. 1. Push phase 2. Stop-and-copy phase 3. Pull phase

  5. Migration Example: • Stop-and-copy => Only stop-and-copy phase • Pure demand-migration => Stop-and-copy phase and Pull phase • Pre-copy => Push phase and Stop-and-copy phase

  6. Pre-copy migration

  7. Challenge in Pre-copy • Every VM have some set of pages which updates very frequently. • And the Sets size would influence downtime of the migration. • Writable Working Sets • The bandwidth of network also impact the migration time.

  8. Implementation • There are two kinds of implementation of migration. • Managed Migration • The physical machine has a management VM. (Xen) • Self Migration • There are three conditions to change into stop-and-copy phase. • The dirty rate is bigger than the upper bound. • The size if working set is small enough. • The limit of the rounds.

  9. Managed Migration(Xen) • 1st round: • Copy all memory pages to destination machine. • Replace originalpage table with shadow page table whose all pages are marked read-only . • Create a dirty bit map for the VM. • 2nd-(n-1)th round: • During the pages transferring, if VM want to modify a page, it will invoke Xen to set the appropriate bit in the dirty bit map. • Dirty pages will be resend again. • Reset dirty bit map for the next round. • nth round: • When the Dirty rate is bigger than up bound, begin to do stop-and-copy.

  10. Self Migration • 1st round: • Copy all memory pages to destination machine. • Mark all virtual address as write-protect. • The OS create a dirty bit map(used to tracking physical pages) to memory the modified pages. • 2nd-(n-1)th round: • During the pages transferring, if write faults occur, OS will set the appropriate bit in the dirty map. • Dirty pages will resend again. • Reset dirty bit map for the next round. • nth round: • When the dirty rate is bigger than the upper bound, OS would disable all activities. • Copy all dirty pages to shadow buffer. • Transfer the buffer and ignore new page updates.

  11. Web Server migration

  12. SPECweb99 benchmark

  13. A worst case example

  14. Optimization • Dynamic Rate-Limiting • Rapid Page Dirtying • Para-virtualized Optimization 1. Ballooning mechanism 2. Stunning rogue Process

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