2011-01-28

Hur funkar Dynamic Memory egentligen i Hyper-v?

Dynamic Memory är en ny feature i SP1 till Windows 2008 R2. Än så länge ligger denna bara som Beta, men många är nyfikna på hur den funkar.
Som tur är så har Maged Ezzat  skrivit ihop en artikel som visar exakt hur man gör på en VM för att aktivera och dessutom hur det hanteras i själva Windows. Ruskigt enkelt förklarat. Sånt tycker vi om. :)

Han refererar också till ett Witepaper om Dynamic Memory som rekommenderas att kika igenom.
En sak jag reagerat i det dokumentet är detta stycke (jag har markerat det jag reagerade på):
In order to be able to dynamically remove memory from a virtual machine, Dynamic Memory employs a process called ballooning. Ballooning works by having the virtual machine and the host agree that certain memory pages will no longer be accessible by the guest. This effectively reduces the amount of memory available to the guest, although system tools such as Task Manager running in the guest operating system will not display any decrease in memory available to the guest. Should the virtual machine later request additional memory from the host, memory pages that were previously ballooned will be unballooned as needed until all ballooned pages have been returned to the guest. Should the guest continue to request additional memory after this, Dynamic Memory allocates more memory to the virtual machine. Note that memory is not instantaneously removed from a virtual machine unless it is instantaneously required for use by another virtual machine.

Frågan är hur detta kommer att fungera i praktiken. Blir det inte så att en maskin alltid kan öka mängden minne men inte krympa den? att "krympningen" görs av balloon-drivern?
Kan bli jobbigt att administrera och få överblick på hur mycket minne maskinerna egentligen använder och behöver. Övervakningsverktygen behöver absolut uppdateras för att hantera denna typ av övervakning...

En annan intressant del är vilka OS som stöder dynamic Memory:

The following Windows server operating systems support Dynamic Memory when installed as the guest operating system on a virtual machine:
- Windows Server 2008 R2 Standard Edition SP1*
- Windows Server 2008 R2 Enterprise Edition SP1
- Windows Server 2008 R2 Datacenter Edition SP1
- Windows Server 2008 R2 Web Edition SP1*
- Windows Server 2008 Standard Edition SP2*
- Windows Server 2008 Enterprise Edition SP2
- Windows Server 2008 Datacenter Edition SP2
- Windows Server 2008 Web Edition SP2*
- Windows Server 2003 R2 Standard Edition SP2 or higher*
- Windows Server 2003 R2 Enterprise Edition SP2 or higher
- Windows Server 2003 R2 Datacenter Edition SP2 or higher
- Windows Server 2003 R2 Web Edition SP2 or higher*
- Windows Server 2003 Standard Edition SP2 or higher*
- Windows Server 2003 Enterprise Edition SP2 or higher
- Windows Server 2003 Datacenter Edition SP2 or higher
- Windows Server 2003 Web Edition SP2 or higher*
Note: The Beta release of Service Pack 1 does not support Dynamic Memory for the operating systems marked with an asterisk (*) above. However, support for Dynamic Memory for these operating systems will be added in a future release of SP1.
Note: Dynamic Memory is supported for both the x86 and x64 architectures of Windows Server 2003, Windows Server 2003 R2 and Windows Server 2008.

The following Windows client operating systems for both x86 and x64 architecture also support Dynamic Memory when installed as the guest operating system on a virtual machine:
- Windows® 7 Enterprise Edition
- Windows 7 Ultimate Edition
- Windows Vista® Enterprise Edition SP2
- Windows Vista Ultimate Edition SP2

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