Dell EqualLogic iSCSI SAN Storage Pricing Performance Virtualisation VMware

SAN Replication offers a simple and cost effective route to disaster recovery. Dell EqualLogic comes complete with SAN based replication as part of the inclusive licensing model, with volumes, groups of volumes or your entire data inventory replicated to a second location using powerful management and scheduling tools. When deployed in conjunction with virtualistion, entire server estates can be recovered and back online in minutes should the production site become compromised.

Many consider synchronous replication - effectively 'mirroring' volumes between locations - to be the 'Holy Grail' of disaster recovery, however this method requires expensive high-bandwidth links and can have a serious impact on performance of production systems. In order for replication to be truly synchronous, disk writes must be committed by both local and remote storage before activity can continue. Many applications will wait for confirmation that writes are complete before they proceed, so where high latency links (inevitably) exist between sites the performance cost will often outweigh the benefits of a real time copy.

Asynchronous replication considers the disk write complete when it is committed to local storage so performance impact is reduced, however this means that data on the recovery site can effectively fall behind with no guarantees that data will be intact or up-to-date should failover be required.

Dell EqualLogic operates a point-in-time snapshot SAN replication model. Building upon the powerful local snapshotting capabilities of the platform, pointer based snapshots can be efficiently replicated through low bandwidth links to achieve a comprehensive recovery model. Application consistent snapshot tools ensure that data is intact for rapid deployment at the recovery site, with no need for consistency checks or time consuming restoration from tape. This method also enables multiple recovery points to be maintained, ensuring that any corruption that occurred as the production site failed is not duplicated to form part of your only recovery option.

Replication takes place between storage pools which can include single or multiple appliances. It is not necessary to operate a like-for-like model, so a 15K SAS PS6000XV appliance can be replicated to an entry-level SATA PS4000 array. Performance following recovery will of course be dictated by the appliances in use, however in almost all circumstances slightly slower applications are enormously preferable to no systems at all!

If you would like further information with regard to SAN replication with EqualLogic storage, developing a disaster recovery model, or if you have any other questions please use the contact form to get in touch.

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