By Eric Siebert
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Storage replication works at the storage subsystem layer and is mostly transparent to virtual hosts and virtual machines (VMs). This approach relies on storage hardware or software that can do synchronous replication 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-continuous data protection (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 disaster recovery site in case of a disruption at the main site. 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.
Part of this guide was originally published in Storage magazine.