Very rarely, data backups are necessary for purposes of restoration due to some type of failure, or catastrophic event. A broken cooling fan or a clogged air vent overheating a hard drive, a server restart without advance warning, or unscheduled maintenance by a technician can cause damage to specific files that may have been open at the time.
For these unforeseen events, performing a complete backup of data on at least a weekly basis is highly recommended. More frequent backups are even better. An established schedule for rotation of backup media, and an off-site storage location for backup media are also highly recommended. Off-site rotation insures that your data is protected in the event of severe physical damage to the servers and/or workstations.
The selection of the media used to store the backup is crucial. This author uses shelf life as a guide to choosing what media to use for backups. CD’s and DVD’s tend to have a greater shelf life than tape cartridges and are relatively sturdy. Tapes, CD’s, and DVD’s are reasonably reliable, although this author has experienced problems from time to time trying to recover data from them. Although removable hard drives are more reliable, removable hard drives are not as compact, and if a removable hard drive is dropped, chances are the data is gone. This author recommends tape cartridge backups with DVD’s as a supplement. A DVD can easily popped intoo the mail to Grandma’s house once a week insuring a reliable off-site rotated backup that can be read by virtually any pc.
A general rule for deciding a frequency and schedule for backup is “how much time can be afforded to re-enter all data for the period of time that has elapsed since the last backup?” Not only the loss of time re-entering lost data is a factor, but consider the margin for error anytime data must be manually entered or re-entered.
The following is an example of a schedule for data backup and off-site rotation assuming a tape backup system with eight tape cartridges (each cartridge has the capacity to store one complete data backup), and that a complete backup is performed once a week:
Label the cartridges Weekly 1, Weekly 2, Weekly 3, Weekly 4, Quarterly 1, Quarterly 2, Quarterly 3, and Quarterly 4. The first weekly backup begins with the cartridge labeled Weekly 1, the second week will use the cartridge marked Weekly 2, and so on. Week number five will use the cartridge marked Weekly 1, week number 6 will use the cartridge marked Weekly 2, and so on. The end of each quarter has its own backup set, the first quarter uses the cartridge marked Quarterly 1, the second quarter uses the cartridge marked Quarterly 2. It is recommended that the quarterly backups be rotated off-site.
This author recommends complete backups as opposed to incremental backups. The latter is a current backup of only those files which have changed since the last backup. The advantage to an incremental backup is that it generally takes less time and tape capacity. The overwhelming disadvantage is the administrative nightmare to glue everything back together in the event you must restore from an incremental backup.
Backed up data should be checked periodically by restoring. The restore can be selective, restore enough of your data to determine that the backup media is valid. Make sure that you are able to read your backup media off-site, preferably by an installation of the application(s) that can read the data.
Consider a worst case scenario; your buildings’ sprinklers activated last night, the deluge of water ruined everything (this author has seen this happen, the customer lost everything, and their only backup was a removable hard drive that had been updated almost a year prior to this event). All of the servers, workstations, tape backup systems, removable hard drives, CD’s, DVD’s were all water damaged beyond repair. This customer had to re-enter a whole year’s worth of data manually, and from paper lists that just happened to be on loan to a branch office.
An example of the importance of offsite backups came to light in January of 1994. Many large office buildings were “red tagged” after the Northridge earthquake hit the greater Los Angeles area. Once a building is red tagged, you are not allowed in to recover anything. This author know s of several doctors who lost all of their data because they left their laptops in their offices and had no offsite backups.
“Fire Proof Safes”
This author knows of an unfortunate incident whereby a gentlemen’s house had burned to the ground in the infamous Malibu, California fire of 1993. He had stored his valuables, important papers, and digital media in his fire proof safe. He was finally able to go back to what was left of his home after the fire had been out for several days. Even though his fireproof safe was still hot from the fire, he opened the door. The instant the door was opened, all of the paper and digital contents vaporized. This author doesn’t profess to understand the thermal dynamics of exactly what happened, but simply put, the safe was hot and its contents were in a vacuum. When the door was opened, much cooler air was allowed in. So much for fireproof safes.