Q: What is the difference between data retention and data archival? The article at http://www.complianceguru.com/2010/11/archiving-vs-retention-of-email-and-other-electronic-data/ seems to suggest there is a difference. It isn't very clear though what if the difference is apart for the length of time it may be stored. 
The description below also suggests that other than archived data e.g. retained data is mutable or changeable. 

Now, retention vs. archiving: Think of an archive as a non-alterable backup.  Some archive solutions also add a search feature, but the key is that the data cannot be deleted or modified in any way.  So why consider archiving instead of simple retention?

Is there a difference and if so what are the differences?

A: "Archiving" is a bit like an overflow car park.  When the main one gets "full", you need somewhere else to park new cars as they arrive.  The difference with an archive is that you move the cars that are already parked but that haven't moved for a while; you shunt these off to the overflow car park (archive) so that the new arrivals can be more easily accessed, nearer the front gate. 
Cars (data) parked in the overflow (archive) are generally ignored, except when you want to search them. 
"Retention" applies to both car parks - regular and overflow - and is when you start issuing parking tickets (or deleting data).  This may be simple housekeeping (Does it really matter anymore that "Fred" accessed a particular web page on your site three years ago?) or may be influenced by accountancy or even legal requirements. 
You don't have to use archiving; if you have enough storage (parking space) and you still get reasonable performance from your queries even with many years of accumulated data, then you don't need archiving (and well done; you database structure must be pretty good).  It is, however, a very common method used to streamline systems by moving the bulk of records, that aren't used every day, into secondary storage.  For example, taking new orders from a customer today probably doesn't need to go through their entire, twenty year transaction history but a once-a-year, Management Information exercise to identify long-term customers would. 

A: Archiving -- take a copy and store it somewhere else.
Retention -- how long you keep the data in a particular store.
So you might archive a copy of your payroll database to tape once a month and send it to an offsite warehouse. So if the IRS demand to know how much you paid Joe Soap in 1998 you can root around the warehouse blow the dust of the tape and hope you did not throw away the tape drive to read it with.
Your accountants may have decided to retain monthly payroll data in the payroll system for seven years. So when the IRS demand to know how much you paid Joan Soap in March 2008 you can access the data with a normal query. 
