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Disaster Recovery Musings
Written by Eric Novikoff   

Here at ENKI we get a lot of questions about DR, probably since the AppLogic technology we base our services on already provides increased resistance to hardware failure, so customers think to themselves, "well, what would it take to tack another nine onto my reliability percentage?"

The traditional wisdom in the IT industry is that each nine of reliability costs you double the amount of money.  For example, going from 99.9% uptime to 99.99% uptime might double your cost because this transition typically requires fully redundant hardware.  AppLogic bypasses these economics to some extent by giving you 3+ nines out of the box (if you know the tricks of  the trade to get the most from it) while only requiring n+1 redundancy rather than 2*n.  This also presupposes that you have fully redundant network hardware, though networking hardware typically reaches three 9's without redundancy. 

To discuss disaster recovery with customers, I have created a table that summarizes my views with respect to AppLogic versus non AppLogic-based options to increase reliability over the reference standard of private server hosting.  It isn't absolute, but it's a great starting point for a discussion.  One note: the DR site solutions listed assume that you aren't using AppLogic at the DR site.  If these sites were deployed with AppLogic in a utility billed model such as ENKI uses, the costs could be reduced dramatically, since the resources allocated to them could be increased once the DR site was actually in use.  Essentially you'd add the "AppLogic-based Hosting" column costs to your current site costs, with additional savings on labor because both sites could be administered through the same process.

 

 

Colocated, Shared, or Virtual Private Server Hosting

AppLogic-based Hosting (VPS or VPDC)

Separate DR Site with cold standby

Separate DR Site with hot standby or active/active configuration

Cost

1x

0.5-1.2x (depending on resources allocated versus non-AppLogic solution)

1.5x-2x  (depending on resources reserved for standby site)

1.8x - 2.5x or more (depending on resource allocation and operations labor costs for remote site)

Recovery time from hardware failure (worst case)

Hours to Days (if backups are difficult to restore or not current)

Minutes

Minutes to hours to start DR site.

Near-instant

Recovery time from total loss of primary site, including finding replacement hosting/hardware

Days to weeks

Hours (assuming application has been backed up off-site and offsite backups available allowing restart in another AppLogic data center.)

Minutes to hours (time is required to start application, load backup data, change DNS)

Near-instant

Transaction Throughput

1x

1x (assuming same resource allocation as collocated/shared server)

1x (assuming same resource allocation as primary site)

1x (hot standby)

1.1x-2x or more if in active/active configuration

Application Architecture

Any, all tiers of application running on one machine, or distributed among multiple machines

Any

Any, but include functions for regular backup to cold standby site

Full duplication with master/slave or master/master database relationship as well as dynamic DNS.  Possible application changes to support distributed data or sessions.

 

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