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<h2>History of Disaster Recovery/High Availability</h2>
Take a walk down DR memory lane with me...

Over the past two decades, the ability of businesses to protect their data from disasters has fundamentally transformed.

15-20 years ago, the best method of protection of business critical data relied upon tape-based backups and transporting them offsite, hoping to be able to recover in the event of a true disaster. Only the Fortune 100 even had locations in which they could recover this data (via services like SunGard), should they have a data loss or facility loss event. Having duplicate systems and separate locations was just too cost prohibitive. All servers were physical, Storage Area Networks were just being deployed, most storage was DAS, and array-based replication technologies were sparse and just beginning to evolve. At best, companies could hope to achieve a 24-48 Recovery Point Objective (RPO) using the offsite tape-based approach. Recovery Time Objectives (RTO) were even longer due to the complexity and often disparate physical systems at a recovery facility.

Fast-forward just five years from that point (1999/2000). Storage Area Networks became more popular due to wider adoption rates which reduced costs. Windows Clustering Services (codename Wolfpack) was introduced to provide some local redundancy, but was more a high availability solution, than a DR solution. Shared storage was a common conversation and having a remote recovery facility wasn’t uncommon.  However, the distraction of Y2K remediation efforts and its associated costs forced lots of other companies to postpone their DR initiatives.  After the Y2K rollover was uneventful, companies began building true DR facilities of their own -building them out as new applications and services were deployed.

The practice was far from common place, but it now became practical. However, for every server deployed in production, a matching system needed to be deployed to the DR facility. This resulted in duplication (2x) of cost for every application, so only top tier applications were protected in this method. The recovery process was still from tape, but it was possible and simplified due to common hardware at both locations.  At this point, synchronous, array-based replication technologies were possible and were being used in real-world scenarios during this time.  Being synchronous replication, it required significant bandwidth between facilities/arrays. Remember, deduplication technologies and inline network-based compression technologies weren’t even invented yet (the server hardware platforms simply couldn’t handle that level of processing). While these solutions were possible and were being done, they were rather complex and were pushing the envelope of technology.

Now, fast forward to 2005.

SAN technologies evolved even further, making centralized storage a common term. Synchronous replication and asynchronous replication were now used to protect data between sites. Asynchronous replication helped alleviate site-to-site bandwidth concerns while still providing data protection. Clustering and host-based replication technologies had advanced and made great strides. However, the biggest transformative change to DR (and server deployment in general) happened during this time period - VMware virtualization software.

This was a HUGE game changer in how companies thought about server deployment and DR. What formerly resulted in two times the cost to protect applications at DR, now got more compressed. Companies would remain physical hosts at their primary location, but consolidate multiple applications at their DR sites on just a few hosts running VMware. Obviously, this greatly reduced costs and opened the doors of DR solutions to even more companies.

In the ensuing years, VMware further decreased server deployment costs and provisioning times. Around this time, VMware developed and released Site Recovery Manager for recovery automation at a DR facility. By integrating with storage array replication technologies, the RPO and RTO times could now be greatly reduced from days and weeks to minutes and hours.

VMware clustering had wide scale adoption for local site high availability, and vMotion/DRS helped in preventing application outages. In addition to the primary storage replication technologies, deduplication and disk based storage platforms were introduced. Data growth during the previous decade had stressed most tape architectures and disk-based solutions offered relief. However, disk based storage still demanded a price premium to tape, and disk solutions didn’t provide an off-site option. By utilizing deduplication, more data could be stored in a smaller footprint and could then be efficiently replicated to a secondary deduplication device at another location. This replicated disk-based backup solution provides a great off-array backup that is protected off-site nearly immediately while providing an effective and consistent 24-hour RPO.
<h2>Where are Disaster Recovery/High Availability Solutions Today?</h2>
eGroup has experienced firsthand all of these transformations in the Storage, Backup, Disaster Recovery, and High Availability technology areas. In fact, our engineers have deployed all of them. There are many dozens of eGroup customers in the Carolinas that you can walk into today and see these technologies in use:
<ul>
	<li>Replicated disk-based backups (Avamar and/or Data Domain) = 24 hour RPO</li>
	<li>Off-site compute capability (both private cloud and eCloud environments)</li>
	<li>Replicated primary-storage system (EMC w/ RecoverPoint has been highly successful) = seconds to 24 hour RPO (bandwidth dependent)</li>
	<li>VMWare HA/DRS = local HA</li>
	<li>VMWare Site Recovery Manager = Reduced RTO</li>
</ul>
All of these technologies are providing significant business value and data protection. However, these technologies ONLY provide either local high availability or remote disaster recovery capabilities (in a down, then up situation). Only one copy of the storage array is writeable at any given time, and therefore failover processes require an application outage so the remote copy can be brought online. Since the Internet age has resulted in the expectation of always available services and systems, the concept of maintenance windows is nearly non-existent.

So, now companies have shifted their focus from DR to more of an HA solution. We're hearing questions like:

How do I leverage both my primary and DR sites to be active-active?; How do I shrink my maintenance windows?; How do I prevent outages?; How do I perform the maintenance activities I need to without causing extended outages?; and, How can I shift workload between sites to address possible impending natural disasters or anticipated outage events (UPS/Generator maintenance – Telecom outages, etc)?

Although the concept of multi-site active/active high availability may sound like an impossible feat, the same was thought about DR two decades ago. In fact, there are technologies available today that can accomplish this objective. To achieve active/active applications and services across two or more sites requires a multi-faceted approach. There are network components, storage components, and the applications have to be designed with HA in mind. From a network perspective, technologies like OTV, TRILL, VPLS, VXLAN, and layer 2 extension can create a uniform IP address space between the locations. From an application perspective, things like Microsoft Exchange DAG (Database Availability Groups) support multi-site deployment out of the box to offer some selective active-active capabilities. However, to offer true workload mobility from site to site, servers at each location need to see a uniform and consistent storage platform. It has been a challenge to offer multiple writeable copies of data at different sites simultaneously.
<h2>Enter EMC VPLEX</h2>
A few years ago, EMC released their VPLEX technology that addresses the high availability questions leveraging what EMC calls “cache coherency" - meaning that each site updates their cache bitmaps instantly across sites so workloads running at each site stay in sync.

VPLEX offers local high availability across multiple storage arrays using virtual volumes (think of it like mirroring a LUN on one array to a LUN on another array). VPLEX can do this same thing across synchronous replication distances (between 60 and 100 miles at &lt;5 ms of latency) using distributed virtual volumes. VPLEX manages the data synchronization between arrays (these arrays can be nearly any Fiber Channel based storage). Once deployed alongside some network virtualization technologies, splitting vSphere clusters across sites is now possible. Since the same IP range and same LUNs are now visible across two separate sites, vMotion can occur seamlessly as can VMware HA recovery.  The applications don’t require IP address changes, and there is no movement of the actual storage from one site to another (which would consume bandwidth). Since this is a synchronous solution, it achieves the zero RPO and RTO that most organizations strive for.

In the event of a site outage, the surviving VPLEX site assumes ownership and any impacted workloads automatically recover. Of course, there are always special considerations and deployment models that need addressed per application, but this platform can realistically provide an always available storage platform. When used in conjunction with other replication technologies (RecoverPoint), yet another copy of data can be sent to a third location for a journal-based recovery in the event of corruption of the primary data copies.

Real-world deployments allow customers to shift workload from one data center to another if a hurricane threatens one location. Some customers shift workload whenever circuit disruptions or power maintenance needs to occur. Other customers shift their workload over to perform maintenance on a storage array. The biggest goal is to avoid outages and disasters and by coupling multiple technologies together (backups, Storage HA, Storage DR), data is always protected and recoverable via several means.
<h2>Summary</h2>
Disaster Recovery and High Availability Solutions have greatly changed in the past two decades.

Objectives that were thought to be impossible are now reality and commonplace. Cost structures have adapted to the point that even small businesses are pursuing DR strategies.

VMware, centralized storage, deduplication, and replication have proven extremely disruptive to how businesses operate over the past 10 years.  VPLEX, network virtualization, workload mobility, and active-active multi-site deployments will be disruptive over the next 10 years.

Achieving a true business continuance solution requires a blended approach and implementation of high availability options, with layered disaster recovery solutions.

High availability and disaster recovery are two entirely different concepts and objectives, but they both play together for a business continuance plan. Leveraging an HA solution, but failing to perform backups still leaves a risk gap. It is important to understand the business requirements and know how to identify your risk gaps.

I hope you enjoyed this walk down memory lane and learned something along the way!