How does Storage VMotion or SVMotion works in VMware vSphere 5.5

How does Storage VMotion or SVMotion works in VMware vSphere 5.5

I have seen many guys asking this question, that how does SVMotion works at background and what are the process that is happening at the backend.

Storage VMotion is really a great feature which enables you to migrate your VM’s storage or Virtual disks from one datastore to another datastore without any downtime and yes now started from vSphere 5.5  using web client, you can do both VMotion and SVMotion of powered ON virtual machines simultaneously which was not possible earlier.



So how storage VMotion works?

So when you do SVMotion, all the non-volatile files that make up a VM is been copied first to the destination datastore i.e. .VMX, swp, snapshots and log files.So how storage VMotion works?

  • It starts a shadow VM on the destination datastore, as shadow VM doesn’t have virtual disks, it sits idle waiting for its virtual disks.
  • VMKernel datamover starts the initial copy of migration from source datastore to destination datastore. Than Mirror driver kicks in that mirror’s I/O between source to destination.
  • As I/O mirroring is in place, vSphere makes a single pass copy of virtual disks from source to destination datastore. And the changes made in between this process are been properly taken care by mirror driver by ensuring all the changes are been reflected on destination datastore also.
  • Once the virtual disk copy gets completed, vSphere quickly suspends and resumes in order transferring control to the shadow VM on the datastore.
  • Once it is confirmed that VM is working properly on the destination datastore, the files on the source datastore gets deleted.


What are the benefits of SVMotion?

  • Using storage VMotion, you can balance utilization on datastores.
  • SVMotion doesn’t require any downtime, so this becomes very helpful during storage upgradation or during any activity on storage side.
  • Using SVMotion you can convert thick disk to thin disk and vice versa.
  • Dynamically optimize storage I/O performance.



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