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Storage replication works at the storage subsystem layer and is mostly transparent to virtual hosts and VMs. This approach relies on storage hardware or software that can do synchronous or asynchronous replication from one storage device to another. Because it happens at the storage layer, the virtualization layer is unaware of the process and all virtual machine data is copied to the disaster recovery site where it will be ready to be used by the virtual hosts if needed. Storage replication requires significant network bandwidth between the main site and recovery site because of the large amounts of data that must be transferred quickly. Many vendors employ technologies such as data deduplication and compression to reduce the amount of data sent over the network. Storage replication is commonly used to achieve near-CDP or CDP to allow for very fast recoveries. VMware's vCenter Site Recovery Manager (SRM) product was designed to work with this method; it relies on storage replication to copy data between the two sites and SRM handles the cutover to the DR site by bringing up the virtual machines at the DR site in case of a disruption at the main site (see "About VMware vCenter Site Recovery Manager," see below). Most storage arrays either have replication built-in or available as a software add-on; a sampling of products that support this method include the following:
- EMC Corp. has a wide variety
- of products that support replication, including its entry-level Celerra Replicator and MirrorView products, and higher-end RecoverPoint (journal-based) and Symmetrix Remote Data Facility (SRDF) products.
- FalconStor Software offers Network Storage Server (NSS), a storage virtualization product that supports replication, as well as Continuous Data Protector, a high-end CDP product.
- Hewlett-Packard (HP) Co. builds replication into its StorageWorks EVA and XP disk arrays, and offers add-on products such as Business Copy, Cluster Extension and Continuous Access software for both the EVA and XP product lines.
- Hitachi Data Systems has both a journal-based replication product called Universal Replicator and a high-end CDP product, TrueCopy Remote Replication.
- NetApp Inc. provides an affordable replication option with MetroCluster, and SnapMirror is the high-end flagship replication product.
|About VMware vCenter Site Recovery Manager|
VMware Inc. developed its vCenter Site Recovery Manager (SRM) product to help automate and simplify the recovery process to a disaster recovery (DR) site. SRM by itself isn't a complete solution for disaster recovery and relies on a supported third-party array replication application to handle the replication of virtual machine (VM) data to a DR site. To certify that storage arrays are supported and integrated with vCenter SRM, VMware works with many storage vendors, including 3PAR, Compellent Technologies, Dell Inc., EMC Inc., FalconStor Software, Hewlett-Packard Co., Hitachi Data Systems, IBM Corp., NetApp Inc., Sun Microsystems (now owned by Oracle Corp.) and Xiotech Corp. vCenter SRM allows you to create recovery plans using vCenter Server, extend recovery plans with custom scripts, perform nondisruptive testing, automate execution of recovery plans with a single command and reconfigure VM networking at the DR site. vCenter SRM provides a nice front-end application that both integrates storage replication with virtualization and automates DR failover in VMware environments.
This was first published in March 2010