[ALUG] Word of the Day: memory ballooning

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Word of the Day  
Daily updates on the latest technology terms | May 28, 2014  
memory ballooning 
Memory ballooning is a memory management technique that allows a physical host to take advantage of unused memory on its guest virtual machines (VMs).
When a host OS is short on physical memory, the hypervisor polls balloon drivers installed on the guests to request available memory. The guests respond by using page-reclaiming algorithms to determine which pages are available and can be assigned to the balloon drivers. The process of assigning available pages to the driver is known as inflating the balloon. Releasing available pages is known as deflating the balloon. 
In a positive sense, memory ballooning allows that the total amount of RAM required by guest virtual machines to exceed the amount of physically available RAM on the host. A problem can occur, however, when a balloon driver inflates to the point where the guest VM no longer has the memory it needs to run processes within the guest. In such a scenario, the guest operating system will start swapping things out to deal with its memory issues. This swap activity can negatively affect performance, depending upon the amount of memory to recoup and/or the quality of the storage IOPS delivered to the VM. 
Other memory-reclaiming techniques include memory overcommit, memory paging, memory mirroring and transparent page sharing. 
  
Quote of the Day 

 "Memory Ballooning is a technique that is only engaged when the host is running low on physical memory.  If you have a host with 60 GB of physical memory available and the virtual machines are only allocated a total of 30GB of memory, then you may never need to know what memory ballooning is all about." - Eric Shanks
 
 
Fun Fact 
In a VMware environment, the balloon driver only activates when memory becomes 
scarce. In a Windows Server 
environment, the balloon driver allocates RAM to the VM on-demand. 
  Related Terms 
Related Terms  
hypervisor
memory overcommit
memory mirroring
memory paging
transparent page sharing
memory management
virtual memory
paging
IOPS 
Related Tags 
Capacity planning for virtualization, Virtual machine provisioning and configuration  
  
Required Reading 
Virtual memory management techniques: A beginner's guide
Learn six virtual memory management techniques for improving memory sharing, preventing shortages and resolving memory overutilization.
Optimizing resources with vSphere memory management techniques
Learn about VMware's vSphere memory management techniques and how they can help you over-allocate memory in a vSphere environment.
Memory methods still differ for Microsoft and VMware
Dig deep into the memory management differences that still remain between Microsoft Hyper-V R2 SP1 and VMware ESX server virtualization.  Stay In Touch 
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