After purchasing the appropriate hardware and media, a backup plan is essentially a thorough media rotation schedule. A backup schedule helps ensure data recoverability over time and covers the maximum number of data loss contingencies. Your backup plan must be consistently implemented and tested.
It is impossible to restore data lost yesterday when the most current backup tape is three months old, or when a defective tape was never tested. You should regularly check the backup logs and perform scheduled test restores to ensure backups are being completed successfully.
It is also recommended that you regularly store normal backups off-site. This protects the company’s data in the event of a fire or other natural disaster. It is important to rotate the media that you store off-site as part of the backup plan.
For a small company implementing a tape backup solution, how often you store tapes off-site depends on how critical the data is. Some companies may elect to take backup tapes home every day; for others, weekly or monthly off-site storage is sufficient.
A small company will typically designate one employee to swap backup tapes in the backup device and store tapes off-site. It is important to clearly and consistently label your backup media. Consider posting the backup schedule and procedures near the backup device for quick reference.
Plans vary based on your company’s need, resources, budget, and other factors. Ultimately, a backup plan should be based on how often your data changes, how valuable it is, and how much you can afford to lose. Because most companies cannot afford to lose several days worth of data, a daily backup plan is recommended. When you develop a backup plan, how many tapes you use, what types of backups you perform, and when tapes are stored off-site are all variables that only you can define. Once your plan is in place, it should be regularly evaluated for effectiveness and modified as necessary.
Four example tape rotation plans are provided below. Each example uses a slightly different schedule and will allow you to see the tradeoffs between different types of plans. Because backup plans vary widely and can be affected by many factors, the following examples are not recommendations and may not fit your particular needs. They should only be used as a guide in designing your own backup plan. The examples in this section do not address the need for spare tapes or scheduling tape replacement, both of which are important in developing a thorough backup plan.
Example 1: Daily Schedule (Weekly Tape Rotation)
This weekly schedule example uses a different backup tape each day of the week for one week. This plan does not account for off-site storage and does not provide good restoration coverage over time. Any data lost more than a week prior will not be recoverable using this plan.
Example 2: Daily Schedule (Bi-weekly Tape Rotation)
This example schedule starts with a normal backup, which is promptly stored off-site, and then you use a different backup tape each day for two weeks. The first daily tape (tape 2) is used again at the beginning of every third week. Incremental backups are performed Monday through Thursday, and normal backups are performed on Friday. The Normal backup tapes (tapes 1, 6, and 11) should be stored off-site on a rotating basis.
You can use tapes with smaller capacity on the days when you are doing incremental backups. The tape size will depend on the amount of data that is changed on a daily basis. Only normal backup tapes need to be large enough to store all the data you need to back up from the server.
Example 2–Daily Schedule (Bi-weekly Tape Rotation)
Extending Example 2, week 3 would reuse tapes 2-5 Monday through Thursday, with tape 1 returning from off-site for the Friday normal backup. Week 4 would reuse tapes 7-10 Monday through Thursday, with tape 6 for the Friday normal backup.
To restore data with this schedule, you will need the last full backup tape and all the tapes used for incremental backups since the last full backup.
For example, if the Small Business Server computer experiences a hard disk failure on Wednesday morning, you will need the full backup from the previous Friday, plus the incremental backups from Monday and Tuesday, to perform the restore. To avoid overwriting newer files with older files, the incremental tapes must be restored in the order in which they were backed up.
Total tapes used in this example: 11
Total protection: 3 weeks
Example 3: Daily Schedule (Bi-weekly Tape Rotation)
This example schedule starts with a normal backup, which is promptly stored off-site and then uses a different backup tape each day of the week for two weeks. Starting the third week, the Monday through Thursday tapes are reused, while a new tape is used for the Friday backup. The fourth week would reuse the Monday through Thursday tapes from week two, with another new tape used for the Friday backup. In addition to the first backup, the backup tapes used on Fridays are stored off-site until the week they are used again. In this example, tapes 1, 6, 11, 12, and 13 are stored off-site on a rotating basis.
Example 3–Daily Schedule (Bi-weekly Tape Rotation)
Extending Example 3, week five would reuse tapes 2-5 Monday through Thursday, with tape 1 returning from off-site for the Friday normal backup. Week six would reuse tapes 7-10 Monday through Thursday, with tape 6 for the Friday normal backup.
To restore data in this example, you would need the last full backup tape. However, because you are not reusing the Friday backup tapes on the same schedule as the Monday through Friday tapes, you could roll back to a previous version of a file that was more than two weeks old.
For example, say a file is infected with a virus on Wednesday of week 2. That file would first be backed up on tape 9, and the last clean copy of the file would be on tape 8. What if a user first discovers the virus on Thursday of week 4? By that time, tape 8 has already been reused, thus overwriting all data with data from week 4. You can still recover a clean copy of the file from tape 6, which was stored off-site and is not scheduled to be reused until week six.
Total tapes Used in this example: 13
Total protection: 5 weeks
Example 4: Daily Schedule (Bi-weekly Incremental Tape Rotation, Monthly Normal Tape Rotation)
This example schedule starts with a normal backup, which is promptly stored off-site, and then uses a mix of incremental and normal backups. In this example, the tapes used for incremental backups are reused every two weeks, while the tapes used for Friday normal backups are reused every three weeks. Additionally, the normal backup performed every fourth Friday is stored off-site. These tapes are rotated every six months.
You can use tapes with smaller capacity on the days when you are doing incremental backups. The tape size will depend on the amount of data that is changed on a daily basis. Only normal backup tapes need to be large enough to store all the data you need to backup from the server.
Example 4–Daily Schedule (Bi-weekly Incremental Tape Rotation,
Monthly Normal Tape Rotation)
Extending Example 4, week five would reuse tapes 2-5 Monday through Thursday, and reuse tape 6 for the Friday normal backup. Week six would reuse tapes 7-10 Monday through Thursday, with tape 11 for the Friday normal backup. Week seven would reuse tapes 2-5 Monday through Thursday, and reuse tape 12 for the Friday normal backup. Week eight would reuse tapes 7-10 Monday through Thursday, and then use tape 14 for the Friday normal backup. Tape 14 would then join tapes 1 and 13 off-site. Starting in week nine, the cycle starts again. Tape 15 would be used on the Friday in week twelve.
Tape 1, which was the first backup performed would not be reused until week 24, giving you almost six full months of system recovery protection.
Total tapes used in this example: 17
Total protection: 23 weeks
Media Rotation
In addition to performing data backups according to a tape rotating schedule, your backup plan should include permanently archiving worn tapes and purchasing new tapes. You should regularly remove old tapes from the rotation and introduce new tapes into the rotation. This prevents backup tapes from wearing out and becoming unreliable. There are several strategies to accomplish this, depending on the number of backup tapes you use to implement your backup plan, the type of backup tapes you use, and the number of times the tape is used. Consult the tape manufacturer’s recommendation for information about replacing backup tapes.
Part three of this three part series on back up and recovery will focus on testing.
