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Mar 19 2010

Sizing Storage for VMware View Linked Clones

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ERRATA: I have amended the sizing formula to include not only the Master Replica, but also the replicas. Please read second part of this article at http://myvirtualcloud.net/?p=779.

One of the great features provided by VMware View Composer is the linked cloning technology. Linked clones are dependent VMs linked to a master VM. A ‘replica’ is a copy of the Parent VM and serves as the Master VM.

Sizing storage for Linked Clones require a little bit more thought then Full Clones, as there is more to be considered. It’s necessary to take in consideration the sizes of the Master Replica, Delta Footprint, Log Files, User Data Disk and overhead.

The Delta contains only the differences from the master VM disk that are unique to the cloned VM, resulting in significant storage savings.

Let’s use the following example: 100 VMs with 20GB disk, 2GB RAM and 2GB User Data disk.

· Master Replica – 20 GB

· Delta Footprint – VM Provisioned Memory x 3 (2048 x 3 = 6144 MB)

· Maximum Log Size – 100 MB

· User Data Disk – 2048 GB

· Overhead 15%

973 GB (100 * (6144MB + 100MB + 2048MB) + 20GB + 124GB)

973 GB (n° VMs * (Delta Footprint + Log + User Data Disk) + Replica + Master Replica + Overhead)

A simplistic comparison with the same number of VMs using Full Clones would look like:

2.2 TB (100 * (20GB + 100MB + 2048MB))

2.2 TB (n° VMs * (Clone + Log + User Disk))

It’s not difficult to calculate storage consumption, but add to it Storage I/O, Datastore Sizing, Tiering ,IP storage; I wouldn’t say this is a 15 min job.

Now, If VMware introduces Thin Provisioning as a feature in View we than have a totally new scenario to analyse. The technology is already available in vSphere stack. Would it look like that?

Linked Cloning vs. Linked Cloning Thin Provisioned vs. Full Cloning Thin Provisioned

There is also Hardware Thin Provisioning at the storage layer to add to the equation.

To learn more about Linked Cloning technology refer to View Manager Administration Guide and View Architecture Design at http://www.vmware.com/support/pubs/view_pubs.html

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Permanent link to this article: http://myvirtualcloud.net/?p=745

12 comments

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  1. Ben Di Qual

    Have you seen the functionality of storage cloning utilities? NetApp have a mature one (RCU 3.0) and EMC are almost there

    http://blogs.netapp.com/virtualstorageguy/2009/12/preview-rapid-cloning-utility-30-vcenter-plug-in.html

    http://virtualgeek.typepad.com/virtual_geek/2010/03/additional-emc-nfs-integration-with-vmware-now-ga.html

  2. Andre Leibovici

    @Ben, yes, they are doing a good job and I have posted before about RCU http://myvirtualcloud.net/?p=341

    I havent’ seen the EMC version yet but in regards to NetApp RCU my only comment is: Unfortunately only manual pools are supported, therefore not very useful for large pools where dynamic provisioning is required.

    Cheers

  3. Ben Di Qual

    @Andre must of missed that one – good point Andrei. I’m waiting for the release of the EMC variant to test.

  4. Abhinav Joshi

    Andre,
    Great article. Storage sizing for VDI is definitely an iterative process as customer requirements change and new technologies are introduced. Also, you need to make sure that you choose the right set of provisioning/management technologies to meet the requirements for all user types in the environment.

    For NetApp deployments, I have seen customers leveraging both linked clones and NetApp RCU to meet the needs for different user types.

    One question, how did you get the number ’3′ in this statement?

    · Delta Footprint – VM Provisioned Memory x 3 (2048 x 3 = 6144 MB)

    Regards,

    Abhinav Joshi

  5. Andre Leibovici

    @Abhinav The initial delta footprint created when linked cloning is 3 times the amount of RAM provisioned. This number will eventually grow up to the size of the master replica according to changes made to the system drive. So, it is important to periodically refresh the VM to avoid running out of storage. The refreshing process delete and re-create the linked-clone.

  6. Emma Wingrave

    Hi Andre,

    Really interesting View sizing posts.

    To confirm the Delta Footprint is including the vswp file and vmss (if suspend is allowed)? Will it always be created at 3 * VM RAM or can you tweak this setting?

    Cheers

    Emma

  7. Appmangler

    Andre,

    Great article, very informative. One note to add when we are trying to figure out IOPS we use tools from LiquidWare labs and Lakeside. Both do a good job of clearly identifying read and write IOPS as well as lows and highs.

    Robert
    http://www.atlantiscomputing.com

  8. dan

    hi,

    how can i do ” sizing memory for vmware view 4.5 linked cloned” ?

    Thanks

  9. Andre Leibovici

    I recommend you to have a look at my VDI Calculator at http://myvirtualcloud.net/?page_id=1076.

    You should be able to calculate the whole infrastructure for your project.

  10. Roland van der Kruk

    Andre,

    I was talking to Peter Grant and he explained the same as you wrote in this article. However in my testing of View 3.0, I couldn’t get the linked clone disk (delta footprint?) to the full 20 GB. I had a ‘shared’ image to which all clones are linked, and the data inside that replica was not going to cost me storage for every linked clone. In this test I had WinXP workstations with a 20 GB hard drive, but only 7 GB was actually filled with WinXP and some apps. The 7 GB was saved on every linked clone. Every linked clone disk/delta footprint could only grow to 13 GB in my example. I wonder if I was wrong or that it changed in View 4.5? or…

  11. Andre Leibovici

    @Roland van der Kruk
    The size of the Delta is not based of contents in your Windows guest NTFS partition. You may be using only 1 GB in addition to the original 7GB and not being able to add more information. The Delta is measured by the amount of bytes committed to the VMDK disk that grows overtime. In saying that, I am not sure if anything has changed since View 3.0 in regards to the delta; however I think so. During my tests in 4.5 I was able to fully utilize the maximum allocation and even noticed that when removing files from the NTFS partition and than writing again the VMDK would not grow anymore if beyond a certain size. I hope this answer to your question.

  12. Christian Fedigan

    good

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