Storage VMotion (SVMotion) Explained

Storage VMotion (SVMotion) was initially introduced as method of relocating VMs of older VMFS file system to a new VMFS file system. Since then its has evolved into a technology that can serve many functions. In a manual configuration it can be use to relocate the files of the VM from datastore to another, however when enabled with Storage DRS and Datastore Clusters – SVMotion provides the engine for moving VMs around to improve overall disk performance, as well as assisting with placing the right VM on the type of storage of its IOPS requirements. In the early days, SVMotion required that VMotion was first configured, since then SVMotion has become a core feature of the vSphere platform, and therefore no such dependency exists.

SVMotion are significantly more intrusive to the vSphere environment than the more common VMotion events. This makes perfect sense because by definition SVMotion means the copying of significant amounts of data. Whereas with VMotion the files of the VM stay still, where the location of the VM moves from host to host. SVMotion can be carried out with moving the VM from the host. So it can be seen as being the polar oppposite of VMotion. With VMotion the VMs files stay still, but the VM is move to different host, with SVMotion the VM stay still, but the files are moved to a different datastore. Due to this increase in on load during the period of SVMotion, it could theoretically degrade the performance of the VM, and if simuluatanous SVMotion are carried out then the overall performance of the vSphere host could be degraded. For this reason many SysAdmin opt to carry out SVMotion at times when the load on the VM and host is at it lowest. VM can be left powered on, but the overall impact is reduced.

There are many different reasons to want to use SVMotion and these include:

  • Decommisioning an old storage array who maintanance warranty is about to expire
  • Switching from one storage protocol (NFS, iSCSI, FC, VSAN) to another.
  • Relocate VMs from a LUN/Volume that is running out of capacity or IOPS (or both)
  • To convert RDM disks to virtual disks

Requirements and Recommendations

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