Before you can have a secure and effective plan for managing your data, you must incorporate a strategy that includes the following information:
• The importance of the data you are backing up
• How often to back up your system
• How many tapes you will use
• When you will use certain tapes
• How you will keep track of your backup information
Choosing a Backup Strategy.
Several tape rotation schemes are described in this chapter. Prior to choosing a strategy to use with your Backup Exec system, you should examine the following questions.
How often should I back up?
While there is no set rule on how often to back up your data, there is one consideration that can help you decide for yourself: What is the cost of recreating data that was added or modified since the last backup?
Calculate the manpower, lost time and/or sales and other costs that would be incurred if your system crashed just before the next backup was to take place (always assume the worst-case scenario). If the cost is excessive, the strategy needs to be adjusted accordingly.
For example, if you have a database containing important customer information that you update several times a day, the cost to recreate that information would probably be quite substantial. On the other hand, the cost to recreate the data for one or two inter-office memos would be considerably less.
Ideally, you would want to do at least one Normal backup of all drives, directories, and files every day. Important files and directories that constantly change may need to be backed up several times a day. For safety reasons, a Normal backup should always be performed before adding new applications or changing your system’s configuration.
How long does the data need to be stored?
The amount of time the data needs to be stored is directly related to the tape rotation scheme you use. For example, if you use one tape and back up every day, your backups will never be more than a day old.
Since tape media is relatively inexpensive when compared to the value of your data, it is a good idea to periodically backup your system on a tape not used in the tape rotation scheme and store it permanently.
The threat of viruses is an issue here also. Some viruses take effect immediately, while others may take days or weeks to cause noticeable damage. Because of this, you should have at least the following backups available to restore at any time:
• 3 daily backups (i.e., Monday, Tuesday, Wednesday)
• A one-week-old Normal backup
• A one-month-old Normal backup
Having these backups available should allow you to restore your system prior to when it became infected.
Important: Be careful not to restore data you think may be infected to a drive that is not infected.
What is the life expectancy of a tape?
Tapes that are used over and over will eventually become old and worn out. When this happens, the success of restoring data from those tapes diminishes. Since tape media is relatively inexpensive, it is a good idea to periodically replace your older tapes with new tapes.
Set a standard as to how long you can use a tape before you replace it based on the backup strategy you use, the number of times you use the tape, and how long you plan to keep the Backup SAN and Tape Backup . Also, if the quality and reliability of a tape becomes questionable (you begin to get tape errors during a backup operation), you should replace the tape.
The suggested standard to be:
• if the tape is used once a week then dispose of after 3 months
• if the tape is used often then dispose of after 6 months
• if the tape is used periodically then dispose of after 12 months.
There are five backup methods:
Method – Description
Normal – Normal backups will back up all selected drives, directories, and files regardless of whether or not they have changed since the last backup (resets the archive bit).
Incremental – Incremental backups will back up only the files that have been created or changed since the last Normal or Incremental backup (resets the archive bit).
Differential – Differential backups will back up all files that have been created or changed since the last Normal backup (does not reset the archive bit).
Copy – Copy backups will back up all selected drives, directories, and files and does not affect subsequent Incremental or Differential backups.
Daily – The Daily Backup method backs up all files with today’s date (created or changed today) and does not affect the files’ backup status (does not reset the archive bit).
Before you can develop your tape rotation scheme, you will need to decide whether you want to do Normal, Incremental, Differential, or Daily backups or a combination. There are advantages and disadvantages to each method. Copy and Daily backups may be performed in addition to the tape rotation scheme selected.
Files are easy to find – Since Normal backups include all data contained on your hard drive, you do not have to search through several tapes to find a file that you need to restore.
There is always a current backup of your entire system on one tape or tape set – If you should need to restore your entire system, all of the most current information is located on the last backup.
Redundant backups – since most of the files on your system rarely change, each backup following the first is just a copy of what has already been backed up.
Normal backups take longer to perform – Depending on how much data you are backing up, Normal backups can be time consuming.
Better use of media – Only files that were created or changed since the last backup are included, so there is much less data storage space required.
Less time required for backup – Incremental backups take much less time than Normal backups to complete.
Files are more difficult to find – Incremental files may be spread across all tapes used since the last Normal backup. You may be required to search several tapes to find the file you want to restore (this is typically not a problem if you use full cataloging and Backup Exec’s Advanced File Selection feature).
Full restoration of your hard drive may be time consuming – Restoring a hard drive will probably require the restoration of data from more than one tape. This can take more time than if all data was on a single tape.