Home > Storage > PowerMax and VMAX > Storage Admin > Dell PowerMax and VMware vSphere Configuration Guide > Copying virtual machines with TimeFinder
Organizations have many different reasons for creating copies of VMFS datastores. Some companies will simply create array snapshots at some regular interval but never link them to targets unless there is an issue (VM needs recovery, etc.). Others use them to mount to a backup host and copy the VMs. Still others run reporting activities on those copies.
The process to clone virtual machines with TimeFinder is essentially the same across the various technologies. Although each type of TimeFinder technology has specific commands tailored to it, there are required steps before and after the copy that must be completed. Therefore rather than show each TimeFinder command, SnapVX will be used as the example technology to demonstrate the process as it is the most commonly seen command in customer environments; however a brief mention of TimeFinder/Clone is included as it is not an emulation in PowerMaxOS 10.
Note: Ideally, virtual machines should be shut down before the metadata and virtual disks associated with the virtual machines are copied. Copying virtual machines after shutting down ensures a clean copy of the data that can be used for back up or quick startup of the cloned virtual machine. Live copies of VMs, however, will be crash-consistent with TimeFinder.[19]
TimeFinder/Clone allows users to quickly replicate an application for immediate use by creating read/write copies directly from the source devices. Creating replicas not attached to snapshots (i.e., SnapVX) reduces steps and resource usage.
Clones, however, are not protected by a snapshot. After clone data is modified, there is no snapshot image that can be used to return the clone to its original state. Therefore, generally clones should not be used for application protection; rather, they are useful in situations where there is a requirement for a quick copy to say test a patch, and then even to restore the patched, modified target data directly back to the source.
When using Solutions Enabler with TimeFinder/Clone, the target storage group and volumes, or individual volumes, must be created ahead of time. Unisphere for PowerMax has the capability to create the storage group and volumes for the user if the clone is taken at the storage group level. Individual volume clones are accomplished through Solutions Enabler.
SnapVX operations are performed using the symsnapvx command to create point-in-time copies (snapshots) of critical data. SnapVX creates snapshots by storing changed tracks (deltas) directly in the Storage Resource Pool (SRP) of the source device. SnapVX snapshots are targetless. There is no target device unless the snapshot is linked. As these are targetless, they only consume minimal cache space rather than actual disk space. If there is ever a need for the application to use the point-in-time data, one can create links from the snapshot to one or more target devices. If there are multiple snapshots and the application needs to find a particular point-in-time copy for host access, one can link and relink until the correct snapshot is located.
SnapVX supports up to 256 snapshots per source device (including any emulation mode snapshots) or 1024 snapshots at the storage group level. The legacy session limits still apply to the emulations. For a more detailed overview of TimeFinder SnapVX functionality including IO flow, refer to the appropriate product guides.
Since TimeFinder/SnapVX provides the flexibility of creating copies of devices without specifying a target, it distinguishes it from all other TimeFinder technologies. This offers customers greater flexibility and functionality to make copies of production data.
The steps to create array copies is the same whether or not a particular virtual machine has a raw device mapping (RDM). However, RDMs devices must be included with the VMFS devices when creating a copy to ensure the VM is complete. Failure to include the RDM devices will result in errors powering on the virtual machine after restoring the copy.
Note: TimeFinder/SnapVX technology also offers the option of copying the data as soon as the target is linked by using the “COPY” option. Typically this should only be done if the linked target is going to be used for an extended period of time. In PowerMaxOS 10, all copies are NOCOPY.
Note: Before undertaking the array snapshot[20] process, if the intended linked target device is currently in use as a VMFS datastore, the VMs should be unregistered and the datastore should be unmounted from the ESXi hosts.
[19] When using TimeFinder/Clone in PowerMaxOS 10, the -consistent flag is required.
[20] SnapVX uses the terminology snapshot when referring to the process of taking a copy of a device(s). It has no association with VMware snapshots. In this whitepaper, a VMware snapshot will always have the modifier “VMware” to distinguish it from the array technology.