Now that you are the owner of a data backup and restore hardware/software package, it's time to set up your data backup and data restore procedures. Here are some methodologies that are in common use.
Full data backup procedures are the easiest to implement but waste the most amount of data storage space. Full backup calls for transferring a copy of all stored data regardless of whether or not that data has been changed since the previous backup was performed. You can see why a strategy like this consumes a lot of storage space.
This type of data backup strategy calls for backing up all files that have changed since the last full backup without regard to whether or not they have been backed up during any interim data backup procedure. This methodology also uses more data storage space than is really neccessary.
This is the most space efficient data backup methodology. With incremental data backup only files which have changed since the last data backup session are copied to tape.
That depends upon your total tape capacity and how fast you need to perform a data recovery. Although a full backup consumes the most storage, it is the easiest to restore, after a failure, because you only have to move the last backup from tape to the affected drives.
On the other hand, doing a full backup once per period, and then performing incremental backups in between, requires less storage space but requires you to restore from each individual backup session until the entire hard drive has been restored.
Rotating your data backup tapes, and deciding where to store them, are two very important decisions which are commonly given very little thought and attention. While storing your data backup tapes in the same building as the computers are in works just fine if you need to perform a data restore to recover from a hardware failure, but it does very little to protect you in case of a building fire or other structural damage. Off site storage is your best choice as long as that storage location is accessible to you 24/7. many small companies use a bank safe deposit box only to discover that they are out of luck if they have to perform data recovery after normal banking hours or on a weekend or bank holiday.
A practical backup tape storage and rotation scheme also saves money by reducing the number of tapes that are required to get the job done.
While there are many methodologies in use, the most common one is the Grandfather-Father-Son (GFS) scheme. It has a long and proven history of working and is the least complicated to understand.
All data is protected using a minimum number of tapes.
Less hardware activity reduces wear on both the tapes and tape heads.
It offers an easy to understand and follow methodology that is likely to beactually performed by your staff.
It offers a relative easy data restore process which should result in full data restoration without any data los due to human error.
In its most basic form, the GFS tape rotation strategy uses a 7-day schedule (Sunday through Saturday), which calls for creating at least one full backup each week and daily full or differential backups according to your internal policies.
Even if you create daily full data backup tapes, the last full backup of the week is considered the "official" weekly data backup.
Regardless of the number of full backups you create during the week, the LAST full backup of the week is considered the WEEKLY backup. You can reuse (recycle) the DAILY and WEEKLY backup tapes or take them off site for permanent storage. For a discussion of when to reuse tapes, see Tape Recycling later in this document.
Here is an example of a GFS data backup strategy:
1. A full backup is done at, say, the last day of each month. This data backup tape is stored off site. This is the Grandfather tape.
2. Another full backup is performed once per week and stored off site for the following week. This is the Father data backup tape.
3. Daily incremental backups are then and are stored on-site for the current week. They are then moved off site. This is the Son data backup tape series.
At the end of a full data backup cycle a set up tapes can be returned to the premises and used to perform the current backups.
The six-tape rotation scheme is another easy to manage and cost effective data backup rotation for any company that does not have a high volume of backup data.
This easy to follow methodology calls for alternating between two full backup tapes every Friday, and then using a different tape on Monday, Tuesday, Wednesday and Thursday to perform either incremental or differential backups.
Here's how it works:
First purchase six backup tapes and label them as follows:
Tape 1 - FRI1
Tape 2 - FRI2
Tape 3 - MON
Tape 4 - TUES
Tape 5 - WED
Tape 6 - THU
Then, starting on a Friday you will perform a full data backup onto the FRI1 tape and store it off site.
Next, on Monday, Tuesday, Wednesday, and Thursday you will perform an incremental or differential data backup onto the appropriate tape for that day of the week.
On that Friday perform a full data backup and store it on the FRI2 tape.Continue this process every week rotating out the Friday tapes.
Although very secure and cost effective, this is one of the most complicated data backup methodologies.
This methodology calls for performing a full backup on five different tape sets which are labeled A, B, C, D and E.
Tape Set A is used on every other backup session; Tape Set B is used for every fourth backup session; Tape Set C is used on every eight sessions; and on through the series.
You can choose to do the data backup sessions nightly, weekly, or whatever other interval works out best for you. Here is an example of how this routine works:
Backup session......Tape set used
1......................A
2......................B
3......................A
4......................C
5......................A
6......................B
7......................A
8......................D
9......................A
10.....................B
11.....................A
12.....................C
13.....................A
14.....................B
15.....................A
16.....................E
These are the most common data backup and tape rotation scenarios. There are others and, of course, you can make up your own as well. The important thing is to pick something that works for you and stick with it. After all, it isn't a matter of when you will have data los and need to perform data recovery, but when.