Can replication replace backup?

Well, since you ask...

Evan Unrue

Product Specialist at Magirus UK

When looking at the topic of Backup and Replication or even Backup Vs Replication, there are a number of facets to both which need to be considered. Traditionally we see replication as something which would provide a remote copy of data for the purposes of either recovery of data or business continuity to facilitate fail over of services; the method and smarts required to do this are defined by both RPO and RTO requirements, coupled with the associated value of data or business impact of downtime.

The challenge with replication, as with most things IT is that there are many flavours of technology which will address different business requirements and levels of protection. Traditional A-Synchronous or Synchronous replication will maintain the latest point in time that has been replicated and will enable you to recover in the event of site failure typically; but there is nothing stopping data corruption being replicated.

There is another option in the form of CDP (Continuous Data Protection), which rather than Synchronously replicating data or using a copy on write or first write mechanism to replicate a point in time, will journal writes as they are committed to disk, time and date stamp them and continuously replicate many points in time to a remote site (Enter the likes of EMC Recoverpoint and Falconstor). CDP replication mitigates the risk of replicating corruption because you have very granular restore capability being able to recover to a specific point in time (even recover a corrupt volume from a remote site). This presents an argument for replacing backup...potentially.

However, not everyone can afford appliance based replication or the Storage array typically required to utilise this technology, not least the fact that this technology is typically capacity licensed (presenting challenges when requiring any level of retention, especially in legal, finance and government where retention and secure disposition of data is a critical requirement).

There are also other reasons why backup is still king in many areas. Backup vendors have come on leaps and bounds over the last few years with technologies like deduplication; the likes of Data Domain provide super efficient storage utilisation with their SISL engine and the likes of quantum aren't far behind with their DXI (arguably).

Also for multi-site implementations, backup seems like less of a complex monster to implement and manage than a complex replication topology (although still complex in many cases). The software is simply better geared to that scenario at the moment, especially when we look at the likes of EMC's Avamar for example, where we are deduplicating data at block level and hashing and checking every bit of data that we back up to ensure we don't have to send duplicate blocks over the LAN/WAN.

Not to forget a mention of those governing bodies in many sectors which still require that a physical tape is vaulted every month, coupled with the traditionalist backup administrators who simply know tape, love tape and want tape. Let's not also forget that some of these enterprise companies have invested large sums of money in their tape infrastructure (not to mention time in integration with their applications) and are going to see the kit through its life cycle to get that return on investment (unless they are presented with a compelling event to do otherwise).

So in summary: for the agile mid-size to large SMB who are not bound by archaic governance and are willing to invest in technology and methods which are less traditional and more cutting edge (which may have its risks), certain replication technologies may be a viable option; but for some of the more constrained and regulated enterprise organisations, I think it will be a while until we see things move that way and traditional backup will very much remain the last line of defence until there is a real shift in the market demonstrates replication as tried and tested when replacing backup.

One last point, to touch on a word which we're all getting drilled with.. let's not forget the cloud! Backing up to the cloud is a very compelling prospect when you don't have to invest in anything but agents and an internet connection to backup. In some cases the larger organisation is also looking to the cloud for secondary/tertiary backups and long term retention; a shift which companies like Commvault have been quick to pick up on with their cloud plug-in for example...

Evan Unrue is a Product Specialist at Magirus UK, the UK arm of the Stuttgart-based IT systems and services supplier.