Before we talk a little bit about Virtual Data Mover, I think it will be the best to explain what Data Mover itself is.
A Data Mover is a component that runs its own operating system (OS). This OPS retrieves data from a storage device and makes it available to a network client. It is basically a gateway to present NAS Storage to end-user. The Data Mover can use the NFS, CIFS and pNFS protocols.
The configuration and control data is stored in the root file system of a physical Data Mover.
Virtual Data Mover
A Virtual Data Mover (often called VDM) is software feature that enables the grouping of CIFS and/or NFS and servers into virtual containers. It is possible to separate CIFS (and/or NFS) from each other and from associated environment. For example, using two VDMs, you can attached different IP addresses, different replication scheme etc.
Each VDM storage its configuration information in its respective VDM root file system. The VDM configuration file is a subset of the configuration files on the physical Data Mover.
Picture above shows the Data Mover and 3 root file systems for VDMs. There are operations that can only be performed at the physical Data Mover level. Operations performed at the Data Mover level affect all VDMs!
These operations include:
- Stop, start, delete services (eg. CIFS)
- Data Mover failover
- Parameter changes
In addition to CIFS servers created on a VDM, a global CIFS server is required for antivirus functionality. It means you have to have one additional CIFS server, created on the physical Data Mover to use AntiVirus solution. In short future I will explain a little bit more regarding EMC CAVA.
Sooner or later I will create a seperate post regarding EMC Replicator, in this paragraph I just want to make a quick introduction to the concept of replication. In order for a CIFS object to be fully functional and accessible on a remote VNX system, the administrator must copy the complete CIFS working environment. That includes local groups, user mapping information, Kerberos objects, shares, event logs etc.. In addition you have to replicate the file systems associated with the CIFS server.
VDM replication accomodates the CIFS working environment by replicating the root file system of the VDM, which includes the CIFS working environment information. Using this form of replication, you will produce a point-in-time copy of a VDM than re-creates the CIFS environment at the destination.
The VDM root file replication does not include the replication of the filesystems mounted to that VDM! What does that mean? That if you replicate only the VDM root file, you will not be able to use your DR site, because the user data itself will not be replicated.
The replication failover procedure verifies that the remote VNX Data Mover has matching network interface(s) [same name] as the interface(s) configured on the source VDM. This check is also applied for all interfaces attached to the VDM regardless of which protocol they are bound.
Source VDMs can be involved in replicating up to four destination VDMs concurrently. A destination VDM must be in a read-only state (called mounted, as opposed to lodaded state, which is in read-write state). A destination VDM can be a source for up to three other replications. Since a given VDM can ac as both a source and destination for multiple replications, it supports a one-to-many and cascade configuration.