Dell MD3600f, MD3620F Remote Replication Concepts

Dell PowerVault MD3600f/MD3620f Remote Replication Functional Guide

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There are some key, critical design issues regarding remote replication that need to be addressed before

designing a DR solution using remote replication.

• Distances involved (primarily the distance between the primary and secondary sites)

• The amount of data required to be replicated

• The recovery objectives should a disaster occur

• The requirements for database applications

For more details about designing a RR solution, please refer to the

Remote Replication Concepts

This section introduces you to primary, secondary, and replication repository, and describes how they

interact to replicate data between arrays using the Remote Replicatio n feature.

When you start remote replication, a replicated virtual disk pair is cr eated and consists of a primary

(local) virtual disk on the primary storage array and its replicat ed pair virtual disk on the secondary

storage array.

Primary (Local) Virtual Disk

The primary virtual disk is the virtual disk that accepts ho st I/O and stores application data. When the

replication relationship is first created, data from the primary virtual disk is copied in its entirety to the

secondary virtual disk. This process is known as a full synchroni zation and is controlled by the local

MD36X0f storage array and owner of the primary virtual disk. During a full synchronization, the

primary virtual disk remains fully accessible for all normal read and write I/O operations. The local

MD36X0f storage array is responsible for initiating remote writes to the secondary virtual disk to keep

the data on the two virtual disks synchronized.

Secondary (Remote) Virtual Disk

The remote or secondary MD36X0f storage array receives remote writes from the primary MD36X0f

storage array and applies these writes to the remote virtual disks. While these secondary virtual

disks(replicas) are also regular virtual disks they are not directly accessible for I/O by any hosts: the

remote storage array will not accept direct host write requests for those virtual disks acting as remote

pairs. This is to prevent unintentional corruption of the data being replicated to these secondary virtual

disks. Virtual disks in secondary mode can be mapped to hosts, and are seen as read only disks until

later promoted to a primary mode (a role reversal). MD36X0f storage also provides a feature that

allows secondary virtual disks to be read through the use of the Sn apshot function.

: Only standard virtual disks may be used in any replicated virtual disk pair (no Snapshot virtual

disks). There can be up to 16 defined virtual disk replication pairs per MD3600f storage array.

Fail Over/Role Reversal

During normal RR operations, the remote virtual disks are in target mode and not in primary virtual disk

mode. This prevents host access of these virtual disks for normal I/O. In the event of a disaster or a

catastrophic failure of the primary site, a role reversal can be performed to promote the secondary