Thursday, 26 March 2015 10:06

Backups & Fault Tolerance: A Rough Overview

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Backup and RestoreBackups & Fault Tolerance: A Rough Overview

Duane MitchellBackup & Fault Tolerance

First a rough definition of backup and fault tolerance. Fault tolerance is an immediate solution to a failure. Backups require a restore process that may take a fair amount of time. An example of fault tolerance is a mirrored hard drive on a server. If one drive fails the server continues to perform on the second hard drive. Another example of fault tolerance is having a fail over system. This is where if one server fails a second identical server immediately takes over. A backup is a software process of, roughly, copying files from a machine onto media of some sort on a scheduled basis.


Backups are the first thing I want to know about in any new evironment. Backups seem to be more confusing now than 10 years ago. There are more options to choose from. Some of these are really just making copies. The problem with that is if you delete something on the original then it is deleted on the backup. A backup refers to a system that is taught freshman year of any IT program. It begins by doing a full backup of the machine followed by daily incremental backups of just the changed files. It keeps copies or versions of all these changed files. After a period of time the media used for the backup is removed and replaced with fresh media. The system then repeats. Most suggest rotating 3 sets of media taking the most recent off site for safe keeping should a disaster occurr. When a media comes back up in the rotation for use it is recycled or reused. That could mean erasing it and starting over or, in the case of some software solutions, just the updated files are replaced while the missing files are deleted thus creating an exact mirror. This is a very fast solution when you have hundreds of gigabytes of data.

Servers & Mirrored Hard DrivesHard Drive Internals

A server is a unique category of machine with special needs for backup and fault tolerance. A server is used by many people in an organization and it's necessary to their work. Uptime is critical. To meet that requirement mirrored hard drives should be installed. A set of mirrored drives means just that: two hard drives that are exact mirrors of one another. If one fails you pull it out and replace it. No downtime to the system though some would recommend replacing both drives at the same time. In fact, some would want two hard drives with serial numbers out of the same manufacture run but that's another discussion. To replace both would result in some planned downtime. This is not a replacement for a backup system. You would also run the backup system described above.

In the small to medium size organization you may want to backup every users machine. There are many solutions for this and we won't go into the details here. In general all machines are backed up to a single media. This media is attached to a single machine that is serving in the role of backup server. An application is installed onto the individual users machines which then kicks off the backup to the backup server.

Cloud BackupMobile Users & Online Backup

Often there are members of an organization who spend a lot of time mobile. Their primary computer may be a laptop. Since they often aren't connected to the network in the office they don't get a good backup from the office backup system. For these users who need a good backup the only solution is an online backup system. There are quite a number to choose from.

Online backup offers many good solutions for all sizes of organizations. It can be expensive. There are many benefits. The two I feel are most important are that the backups are automated and the data is stored off site. You do need a good internet connection. These online services are improving and updating their offerings all the time. It's a very competitive service at this time. We won't go into the details as this would be a separate discussion.

Website Backups

Automated daily website backups are only offered by better hosting services. All hosting services offer backup but often it's an unusable backup. You have to do a test restore to know. We offer hosting that does include twice daily automated backup. Both the database and the files are stored in a vault where, using the cPanel, you can roll your site back to any date or time in the backup. It's fast and with no downtime to the website. This system stores backups for 30 days. We take monthly backups and store them indefinitely.


Whatever system you use it should be tested periodically for integrity. Backups are easy to forget and can be viewed as a nuisance. However, they are critical to your data integrity. Automated backups are best as you don't need to do any thinking. If you are interested in discussing your backup needs feel free to contact us.

Last modified on Tuesday, 31 March 2015 12:56

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