My personal method of storage for the past 6 years has been the following;
A raid 5 storage array. This requires an enclosure or dedicated standalone Server with a minimum of 3 hard drives where a certain percentage of each hard drive contains the parity for the other hard drives.
If any one of the hard drives fail, the system will continue working, you simply replace the broken hard drive and the new hard drive will auto build itself and bring the array back to a 3 hard drive configuration.
Most units will allow for more than 3 hard drives providing huge scalability for the future increase in storage requirements. The array in most cases will also allow for redundancies. Simply put, you can add extra drives in the enclosure that will only become operational once there is a hard drive failure as it will simply rebuild itself to form the complete storage space.
When the unit is running close to capacity, the user can add further drives. You can buy these in iSCSI or Fibre making the performance ideal for a realtime photo editing session.
To have such a configuration, unless you are IT savvy, you will need the help of a specialist as there are requirements for the understanding of Server Software, plus such a system is not cheap and will require the purchase of a high end PC or a basic server. The user may also wish to have his own personal DR site and have a second such system elsewhere mirroring the changes in realtime, or go for the below,
The next step to this; I recently took out a contract with an online rackspace for cloud storage. For a minimal fee, they back this array of mine as and when required by me. I can set it, real time, hourly, or weekly, it is very flexible.
Although, currently such a system runs in the Terabyte category, it has the potential to exceed well into the Petabyte range and serve for many years to come.
On its own, a Raid 5 solution cannot be considered a true backup solution, and is only as secure as the premises it resides in and therefore is vulnerable and open to fires, theft and other disasters, thus the reasons mentioned above for a second unit elsewhere or cloud backup.
In the past, such storage units were backed up periodically onto Magnetic Tapes and stored in fireproof safes, a method which is still being used today by some banks and government establishments.
I am aware of photographers who use Mag Media, IE LTO Tapes.
What a Raid 5 Storage Array provides, is a very safe way of storing data locally. rather than have a 2 drives mirrored, it spreads this over multiple drives, with each drive having just enough Parity information about the other drives so that if one drive fails, the array continues to work and the faulty drive can easily be replaced. the more drives; the more secure. However, what you see on your PC/Mac, is one volume. Raid 5 has been the chosen method of storage throughout the industry for many years.
However, for the sake of Disaster Recover, it is imperative that this is backed up, but as Data has grown, so has the backup times and it is no longer acceptable to have long downtimes or systems running slow when being backed up. this has given rise to Realtime backup and SAN Storage and very quickly has become the De facto choice for all professionals.
These are basically a large Library of drives in a Raid configuration, to form one single volume(Disk) and replicated at another location to provide a proper Dr solution.
As the users work, their work is always opened and closed within the SAN and nothing is ever stored locally on the Desktop. This means that there is no need for a timed backup as everything is always stored on multiple drives and replicated at another site providing a true real-time backup.
Most Professional agencies who require the Pro Photographer to submit their photos at the end of any session, usually have such a system of storage as they are the Copyright holders.
As for the photographer who works from his own studio, we need a similar system, but one which is cost effective but fast as we also need to do editing and with cheaper SAN servers not always being able to work at block level, brings the need for a more localised storage system, and therefore, the most secure of such systems is a Raid 5 Storage Array which allows for striping and mirroring.
As a standalone, it is the most secure storage method available, but for a true backup, you either need to replicate the storage to another site, or utilise the cloud to do auto backups.
Please note, a Raid 5 is only as fast as the slowest Drive installed.
As a final Note
This Raid 5 Storage method with online cloud back is one that I have chosen and is only one possible solution to the problem of ever growing data. If my data was growing at a slower rate, I may have considered using Raid 1+0 which theoretically would have been faster, but not as scalable as a Raid 5. My Decision was based on long term growth and ease of scalability.
In no uncertain terms, am I promoting or selling such a solution but I have encouraged a lot of my fellow photographers who have also benefitted from the same solution. some of us have even considered sharing our storage in a consolidated closed Network thus eliminated the need for cloud altogether.