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Data Backup and Recovery

from Chapter 14, Microsoft Windows 2000 Administrator's Pocket Consultant by William R. Stanek.

Because data is the heart of the enterprise, it's crucial for you to protect it. And to protect your organization's data, you need to implement a data backup and recovery plan. Backing up files can protect against accidental loss of user data, database corruption, hardware failures, and even natural disasters. It's your job as an administrator to make sure that backups are performed and that backup tapes are stored in a secure location.

Creating a Backup and Recovery Plan

Data backup is an insurance plan. Important files are accidentally deleted all the time. Mission-critical data can become corrupt. Natural disasters can leave your office in ruin. With a solid backup and recovery plan, you can recover from any of these. Without one, you're left with nothing to fall back on.

Figuring Out a Backup Plan

It takes time to create and implement a backup and recovery plan. You'll need to figure out what data needs to be backed up, how often the data should be backed up, and more. To help you create a plan, consider the following:

  • How important is the data on your systems? The importance of data can go a long way in helping you determine if you need to back it up—as well as when and how it should be backed up. For critical data, such as a database, you'll want to have redundant backup sets that extend back for several backup periods. For less important data, such as daily user files, you won't need such an elaborate backup plan, but you'll need to back up the data regularly and ensure that the data can be recovered easily.

  • What type of information does the data contain? Data that doesn't seem important to you may be very important to someone else. Thus, the type of information the data contains can help you determine if you need to back up the data—as well as when and how the data should be backed up.

  • How often does the data change? The frequency of change can affect your decision on how often the data should be backed up. For example, data that changes daily should be backed up daily.

  • How quickly do you need to recover the data? Time is an important factor in creating a backup plan. For critical systems, you may need to get back online swiftly. To do this, you may need to alter your backup plan.

  • Do you have the equipment to perform backups? You must have backup hardware to perform backups. To perform timely backups, you may need several backup devices and several sets of backup media. Backup hardware includes tape drives, optical drives, and removable disk drives. Generally, tape drives are less expensive but slower than other types of drives.

  • Who will be responsible for the backup and recovery plan? Ideally, someone should be a primary contact for the organization's backup and recovery plan. This person may also be responsible for performing the actual backup and recovery of data.

  • What is the best time to schedule backups? Scheduling backups when system use is as low as possible will speed the backup process. However, you can't always schedule backups for off-peak hours. So you'll need to carefully plan when key system data is backed up.

  • Do you need to store backups off-site? Storing copies of backup tapes off-site is essential to recovering your systems in the case of a natural disaster. In your off-site storage location, you should also include copies of the software you may need to install to reestablish operational systems.

The Basic Types of Backup

There are many techniques for backing up files. The techniques you use will depend on the type of data you're backing up, how convenient you want the recovery process to be, and more.

If you view the properties of a file or directory in Windows Explorer, you'll note an attribute called Archive. This attribute often is used to determine whether a file or directory should be backed up. If the attribute is on, the file or directory may need to be backed up. The basic types of backups you can perform include

  • Normal/full backups All files that have been selected are backed up, regardless of the setting of the archive attribute. When a file is backed up, the archive attribute is cleared. If the file is later modified, this attribute is set, which indicates that the file needs to be backed up.

  • Copy backups All files that have been selected are backed up, regardless of the setting of the archive attribute. Unlike a normal backup, the archive attribute on files isn't modified. This allows you to perform other types of backups on the files at a later date.

  • Differential backups Designed to create backup copies of files that have changed since the last normal backup. The presence of the archive attribute indicates that the file has been modified and only files with this attribute are backed up. However, the archive attribute on files isn't modified. This allows you to perform other types of backups on the files at a later date.

  • Incremental backups Designed to create backups of files that have changed since the most recent normal or incremental backup. The presence of the archive attribute indicates that the file has been modified and only files with this attribute are backed up. When a file is backed up, the archive attribute is cleared. If the file is later modified, this attribute is set, which indicates that the file needs to be backed up.

  • Daily backups Designed to back up files using the modification date on the file itself. If a file has been modified on the same day as the backup, the file will be backed up. This technique doesn't change the archive attributes of files.

In your backup plan you'll probably want to perform full backups on a weekly basis and supplement this with daily, differential, or incremental backups. You may also want to create an extended backup set for monthly and quarterly backups that includes additional files that aren't being backed up regularly.

Tip You'll often find that weeks or months can go by before anyone notices that a file or data source is missing. This doesn't mean the file isn't important. Although some types of data aren't used often, they're still needed. So don't forget that you may also want to create extra sets of backups for monthly or quarterly periods, or both, to ensure that you can recover historical data over time.

Differential and Incremental Backups

The difference between differential and incremental backups is extremely important. To understand the distinction between them, examine Table 14-1. As it shows, with differential backups you back up all the files that have changed since the last full backup (which means that the size of the differential backup grows over time). With incremental backups, you only back up files that have changed since the most recent full or incremental backup (which means the size of the incremental backup is usually much smaller than a full backup).

Table 14-1 Incremental and Differential Backup Techniques

Day of Week

Weekly Full Backup with Daily Differential Backup

Weekly Full Backup with Daily Incremental Backup

Sunday

A full backup is performed.

A full backup is performed.

Monday

A differential backup contains all changes since Sunday.

An incremental backup contains changes since Sunday.

Tuesday

A differential backup contains all changes since Sunday.

An incremental backup contains changes since Monday.

Wednesday

A differential backup contains all changes since Sunday.

An incremental backup contains changes since Tuesday.

Thursday

A differential backup contains all changes since Sunday.

An incremental backup contains changes since Wednesday.

Friday

A differential backup contains all changes since Sunday.

An incremental backup contains changes since Thursday.

Saturday

A differential backup contains all changes since Sunday.

An incremental backup contains changes since Friday.

Once you determine what data you're going to back up and how often, you can select backup devices and media that support these choices. These are covered in the next section.

Selecting Backup Devices and Media

Many tools are available for backing up data. Some are fast and expensive. Others are slow but very reliable. The backup solution that's right for your organization depends on many factors, including

  • Capacity The amount of data that you need to back up on a routine basis. Can the backup hardware support the required load given your time and resource constraints?

  • Reliability The reliability of the backup hardware and media. Can you afford to sacrifice reliability to meet budget or time needs?

  • Extensibility The extensibility of the backup solution. Will this solution meet your needs as the organization grows?

  • Speed The speed with which data can be backed up and recovered. Can you afford to sacrifice speed to reduce costs?

  • Cost The cost of the backup solution. Does it fit into your budget?

Common Backup Solutions

Capacity, reliability, extensibility, speed, and cost are the issues driving your backup plan. If you understand how these issues affect your organization, you'll be on track to select an appropriate backup solution. Some of the most commonly used backup solutions include

  • Tape drives Tape drives are the most common backup devices. Tape drives use magnetic tape cartridges to store data. Magnetic tapes are relatively inexpensive but aren't highly reliable. Tapes can break or stretch. They can also lose information over time. The average capacity of tape cartridges ranges from 100 MB to 2 GB. Compared with other backup solutions, tape drives are fairly slow. Still, the selling point is the low cost.

  • Digital audio tape (DAT) drives DAT drives are quickly replacing standard tape drives as the preferred backup devices. DAT drives use 4 mm and 8 mm tapes to store data. DAT drives and tapes are more expensive than standard tape drives and tapes, but they offer more speed and capacity. DAT drives that use 4 mm tapes can typically record over 30 MB per minute and have capacities of up to 16 GB. DAT drives that use 8 mm tapes can typically record more than 10 MB per minute and have capacities of up to 36 GB (with compression).

  • Auto-loader tape systems Auto-loader tape systems use a magazine of tapes to create extended backup volumes capable of meeting the high-capacity needs of the enterprise. With an auto-loader system, tapes within the magazine are automatically changed as needed during the backup or recovery process. Most auto-loader tape systems use DAT tapes. The typical sys tem uses magazines with between 4 and 12 tapes. The main drawback to these systems is the high cost.

  • Magnetic optical drives Magnetic optical drives combine magnetic tape technology with optical lasers to create a more reliable backup solution than DAT. Magnetic optical drives use 3.5-inch and 5.25-inch disks that look similar to floppies but are much thicker. Typically, magnetic optical disks have capacities of between 1 GB and 4 GB.

  • Tape jukeboxes Tape jukeboxes are similar to auto-loader tape systems. Jukeboxes use magnetic optical disks rather than DAT tapes to offer high-capacity solutions. These systems load and unload disks stored internally for backup and recovery operations. Their key drawback is the high cost.

  • Removable disks Removable disks, such as Iomega Jaz, are increasingly being used as backup devices. Removable disks offer good speed and ease of use for a single drive or single system backup. However, the disk drives and the removable disks tend to be more expensive than standard tape or DAT drive solutions.

  • Disk drives Disk drives provide the fastest way to back up and restore files. With disk drives, you can often accomplish in minutes what takes a tape drive hours. So when business needs mandate a speedy recovery, nothing beats a disk drive. The drawbacks to disk drives, however, are relatively high costs and less extensibility.

Before you can use a backup device, you must install it. When you install backup devices other than standard tape and DAT drives, you need to tell the operating system about the controller card and drivers that the backup device uses. For detailed information on installing devices and drivers, see the section of Chapter 2 entitled "Managing Hardware Devices and Drivers."

Buying and Using Tapes

Selecting a backup device is an important step toward implementing a backup and recovery plan. But you also need to purchase the tapes or disks, or both, that will allow you to implement your plan. The number of tapes you need depends on how much data you'll be backing up, how often you'll be backing up the data, and how long you'll need to keep additional data sets.

The typical way to use backup tapes is to set up a rotation schedule whereby you rotate through two or more sets of tapes. The idea is that you can increase tape longevity by reducing tape usage and at the same time reduce the number of tapes you need to ensure that you have historic data on hand when necessary.

One of the most common tape rotation schedules is the 10-tape rotation. With this rotation schedule, you use 10 tapes divided into two sets of 5 (one for each weekday). As shown in Table 14-2, the first set of tapes is used one week and the second set of tapes is used the next week. On Fridays, full backups are scheduled. On Mondays through Thursdays, incremental backups are scheduled. If you add a third set of tapes, you can rotate one of the tape sets to an off-site storage location on a weekly basis.

Table 14-2 Using Incremental Backups

Day of Week

Tape Set 1

Tape Set 2

Friday

Full backup on Tape 5

Full backup on Tape 5

Monday

Incremental backup on Tape 1

Incremental backup on Tape 1

Tuesday

Incremental backup on Tape 2

Incremental backup on Tape 2

Wednesday

Incremental backup on Tape 3

Incremental backup on Tape 3

Thursday

Incremental backup on Tape 4

Incremental backup on Tape 4

Tip The 10-tape rotation schedule is designed for the 9 to 5 workers of the world. If you're in a 24 x 7 environment, you'll definitely want extra tapes for Saturday and Sunday. In this case, use a 14-tape rotation with two sets of 7 tapes. On Sundays, schedule full backups. On Mondays through Saturdays, schedule incremental backups.

from Microsoft Windows 2000 Administrator's Pocket Consultant by William R. Stanek. Copyright © 1999 Microsoft Corporation.

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