XenClient Best Practices Series - Keep on top of your VHD chains

XenClient Best Practices Series - Keep on top of your VHD chains -

Preface

If you're so these people looking under cover XenClient or probably have read a blog earlier about how XenClient operates chaining VHD, you may wonder if there is any way how you can manage some of your strings vhd

the answer is (Choose one) :. Type - Depends - Sure!

technical point of view, you can modify all aspects of VHD files and chains. However, there are some things you need to know: You can easily drag your VHD, so the VM wont boot up - There is no cancel button - Technical support can help you - do not blame me

pain with chain

although VHD chaining is a fantastic technology, there is a good chance that you loose track of the files belong that string. Furthermore, strings can got longer and longer during the life of a virtual machine.

At first, I wanted to share some CLI, how to get more ideas about your chains.

In the second step, I will show you how you can control the proces vhd COALESCE in XenClient

Show me the chain please

the first thing you probably want to know is how do I read these lines.

There are multiple ways to do, obviously, the first thing is to know who belongs vhd my vm here is an example how you can find it:

1. Open terminal
2. Enter: xec-vm -> it will show / UUID mapping you [VM

3. Read the respective configuration file by using the UUID eg
   
   
4. Look for the "disc"
   
5. the VHD file on "disc 1" is that the virtual machine will of - the leaf of the chain typically
6. now we will read the header of this VHD file using the tool vhd-util
   
7. You can see that this VHD file is actually a differentiation HDD and later on name of the parent can be read
   
8. now, you can repeat the steps with the VHD file parent and "walk the line"
9. TIP: use the following command to display the channels VHD in your storage directory:
   
10. output will give you a tabbed list of sorting VHD VHD files against the chain
    Note :. Our chain harddisk VM consists of 3 VHD files
    

which makes the growth of chains

[1945004?] Typically, a string is created each time your system allows instant. snapshot creation will make the current CHD readonly file, so an empty VHD file is created that has all changed since the snapshot -. This is often referred to the sheet

In a world of XenClient, there are many situations when a snapshot is created. By default each time you download an image of the Synrhonizer, the first thing XenClient made after installation of the image is to create a snapshot.

If you use dynamic image mode, you can superimpose the image, creating a gold and referenced differential files statue (diff level HDV compressed block), which are perfect for:

• Registration of bandwidth and storage
• maintaining multiple versions - You, can switch between them by just selecting a different version of an image

When ever a backup is made, XenClient will snapshot of the current sheet, create a vacuum and to download the old (read only) leaves to the synchronizer. After the backup was made the VHD chain will be "merged" in a housekeeping task. This is called coalescence and will work with a low priority in the background.

No worries, if the user is Shuting down the houskeeping XenClient will be continued on the next race until the treatment is completed. However, if it does not end until the next backup program is touched, the chain grows again ...

I want to control the process VHD coalesce

Sometimes you may want to get control of these processes. Guess what, many things in this XenClient is possible that you need to get juice to the terminal.

In order to have something to show, I'll create a manual backup of VM m.

As you can see on the next scan, the same chain of VHD, we examined before knowing four VHD0s opposed to three.

control to the user to control the coalescence process is bed coalasce - you can check which programs are awaiting coalescence using the goals , you can stop using the cancel or activate a canceled job using the enable or simply monitor the state with the monitor .

you can safely message and ruby erro monitoring may not be accurate, but you will get the message coalesce over after the work is completed.

What can I do with these chains

To be frankly honest in a managed environment (using Synchronizer) not much without breaking the system.

Considering the dynamic picture mode each version will add a VHD to the chain and we can switch between versions if these layers are intact. Using the vhd-util "raw" would allow you to merge all channels on the level of vhd, but the backend is not aware of opportunities and dampen VM.

I'v plans to add a share tips about handling VHD in an unmanaged environment in a future blog XenClient Best Practices Series.

Enjoy work with XenClient! Cheers, walter.hofstetter [at] eu.citrix.com

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