Advanced Backup and Restore

Now that you have created a backup plan and verified your procedures for backup and restore, you will want to understand the process in more depth so that you can configure backup operations to be more flexible, more automated or perhaps even easier. This topic will explore the technologies underlying data backup, such as VSC and RSM, and will lay out options for scripting and scheduling backup operations. You will then leverage the new Shadow Copies Of Shared Folders feature to enable users to recover from simple data loss scenarios without administrative intervention.


Understanding VSS

Windows Server 2003 offers VSS, also referred to as “snap backup.” VSS allows the backing up of databases and other files that are held open or locked due to operator or system activity. Shadow copy backups allow applications to continue to write data to a volume during backup, and allow administrators to perform backups at any time without locking out users or risking skipped files.

Although VSS is an important enhancement to the backup functionality of Windows Server 2003, it is nevertheless best practice to perform backups when utilization is low. If you have applications that manage storage consistency differently while files are open, that can affect the consistency of the files in the backup of those open files. For critical applications, or for applications such as Microsoft SQL Server that offer native backup capabilities, consult the documentation for the application to determine the recommended backup procedure.

Backup Security

You must have the Backup Files And Directories user right, or NTFS Read permission, to back up a file. Similarly, you must have the Restore Files And Directories user right, or NTFS Write permission to the target destination, to restore a file. Privileges are assigned to both the Administrators and Backup Operators groups, so the minimum required privileges can be given to a user, a group, or a service account by nesting the account in the Backup Operators group on the server.

Users with the Restore Files And Directories user right can remove NTFS permissions from files during restore. In Windows Server 2003, they can additionally transfer ownership of files between users.

Therefore, it is important to control the membership of the Backup Operators group and to physically secure backup tapes. A “loose” backup tape makes it easy for any intelligent individual to restore and access sensitive data.

Managing Media

The Backup Utility of Windows Server 2003 works closely with the RSM service. RSM, which is designed to manage robotic tape libraries and CD-ROM libraries, accepts requests for media from other services or, in this case, applications, and ensures that the media is correctly mounted or loaded.

RSM is also used with single-media devices, such as a manually loaded backup tape drive, CD-ROM, or Iomega Jaz drive. In the case of single-media drives, RSM keeps track of media through their labels or serial numbers. The impact of RSM is that, even in a single-media drive backup system, each tape must have a unique label.

Media Pools

The Backup Utility of Windows Server 2003 manages tapes with RSM using media pools, as seen in Below Figure.

There are four media pools related to backup:

■Unrecognized: Tape media that are completely blank or in a foreign format are contained in the unrecognized pool until they are formatted.

■Free: This pool contains newly formatted tape media, as well as tapes that have been specifically marked as free by an administrator. Free media can be moved into the backup media pool by writing a backup set to them.

■Backup: This pool contains media that have been written to by the Backup Utility. The Backup Utility will only write to media in the Free media pool (and it will label the tape with the name you enter just before starting the backup) and to media, specified by name, in the Backup media pool.

■Import: This pool contains tape media that are not cataloged on the local disk drive. Cataloging such a tape will move the tape into the backup media pool.

Managing Tapes and Media Pools

In conjunction with backup procedures and tape rotation, you will need to manage your tapes in and out of these media pools. To that end, the following actions are avail-able from the Restore And Manage Media page of the Backup Utility:

■Format a tape: Right-click a tape and choose Format. Formatting is not a secure way to erase tapes. If you need to erase tapes for legal or security reasons, use an appropriate third-party utility. Formatting does, however, prepare a tape and move it into the free media pool. Not all drives support formatting.

■Retension a tape: Right-click a tape and choose Retension. Not all drives sup-port retensioning.

■Mark a tape as free: Right-click a tape and choose Mark As Free. This moves the tape into the free media pool. It does not erase the tape. If you need to erase tapes for legal reasons, use an appropriate third-party utility.

Catalogs

When the Backup Utility creates a backup set, it also creates a catalog listing files and folders included in the backup set. That catalog is stored on the disk of the server (the local or on-disk catalog) and in the backup set itself (the on-media catalog). The local catalog facilitates quick location of files and folders to restore. The Backup Utility can display the catalog immediately, rather than load the catalog from the typically slower backup media. The on-media catalog is critical if the drive containing the local catalog has failed, or if you transfer the files to another system. In those cases, Windows can recreate the local catalog from the on-media catalog.

The Restore And Manage Media page of the Backup Utility allows you to manage catalogs, as follows:

■Delete Catalog: Right-click a backup set and choose Delete Catalog if you have lost or damaged the backup media or if you are transferring files to another system and no longer require its local catalog. The on-media catalog is not affected by this command.

■Catalog: A tape from a foreign system that is not cataloged on the local machine will appear in the import media pool. Right-click the media and choose the Catalog command. Windows will generate a local catalog from the tape or file. This does not create or modify the on-media catalog.

Backup Options

Backup options are configured by choosing the Options command from the Tools menu. Many of these options configure defaults that are used by the Backup Utility and the command-line backup tool, Ntbackup. Those settings can be overridden by options of a specific job.

General Options

The General tab of the Options dialog box includes the following settings:

■Compute Selection Information Before Backup And Restore Operations: Backup estimates the number of files and bytes that will be backed up or restored before beginning the operation.

■Use The Catalogs On The Media To Speed Up Building Restore Catalogs On Disk: If a system does not have an on-disk catalog for a tape, this option allows the system to create an on-disk catalog from the on-media catalog. However, if the tape with the on-media catalog is missing or if media in the set is damaged, you can deselect this option and the system will scan the entire backup set (or as much of it as you have) to build the on-disk catalog. Such an operation can take several hours if the backup set is large.

■Verify Data After The Backup Completes: The system compares the contents of the backup media to the original files and logs any discrepancies. This option obviously adds a significant amount of time for completing the backup job. Discrepancies are likely if data changes frequently during backup or verification, and it is not recommended to verify system backups because of the number of changes that happen to system files on a continual basis. So long as you rotate tapes and discard tapes before they are worn, it should not be necessary to verify data.

■Backup The Contents Of Mounted Drives: A mounted drive is a drive volume that is mapped to a folder on another volume’s namespace, rather than, or in addition to, having a drive letter. If this option is deselected, only the path of the folder that is mounted to a volume is backed up; the contents are not. By selecting this option, the contents of the mounted volume is also backed up. There is no disadvantage in backing up a mount point, however if you back up the mount point and the mounted drive as well, your backup set will have duplication.

If you primarily back up to file and then save that file to another media, clear the following options. If you primarily back up to a tape or another media managed by Removable Storage, select the following options.

■Show Alert Message When I Start the Backup Utility And Removable Storage Is Not Running.

■Show Alert Message When I Start The Backup Utility And There Is Recognizable Media Available.

■ Show Alert Message When New Media Is Inserted.

■ Always Allow Use Of Recognizable Media Without Prompting.


Backup Logging

The Options dialog has a tab called Backup Log. Logging alerts you to problems that might threaten the viability of your backup, so consider your logging strategy as well as your overall backup plan. Although detailed logging will list every file and path that was backed up, the log is so verbose you are likely to overlook problems. Therefore, summary logging is recommended, and is the default. Summary logs report skipped files and errors.

The system will save 10 backup logs to the path %UserProfile%\Local Settings \Application Data\Microsoft\Windows NT\Ntbackup\Data. There is no way to change the path or the number of logs that are saved before the oldest log is replaced. You can, of course, include that path in your backup and thereby back up old logs.

File Exclusions

The Exclude Files tab of the Options dialog box also allows you to specify extensions and individual files that should be skipped during backup. Default settings result in the Backup Utility’s skipping the page file, temporary files, client-side cache, debug folder, and the File Replication Service (FRS) database and folders, as well as other local logs and databases.

Files can be excluded based on ownership of the files. Click Add New under Files Excluded For All Users to exclude files owned by any user. Click Add New under Files Excluded For User if you want to exclude only files that you own. You can specify files based on Registered File Type or based on an extension using the Custom File Mask. Finally, you can restrict excluded files to a specific folder or hard drive using the Applies To Path and the Applies To All Subfolders options.

Advanced Backup Options

After selecting files to back up, and clicking Start Backup, you can configure additional, job-specific options by clicking Advanced. Among the more important settings are the following:

■Verify Data After Backup: This setting overrides the default setting in the Backup Options dialog box.

■If Possible, Compress The Backup Data To Save Space: This setting compresses data to save space on the backup media, an option not available unless the tape drive supports compression.

■Disable Volume Shadow Copy: VSS allows the backup of locked and open files. If this option is selected, some files that are open or in use may be skipped.


The Ntbackup Command

The Ntbackup command provides the opportunity to script backup jobs on Windows Server 2003. Its syntax is

Ntbackup backup {"path to backup" or "@selectionfile.bks"} /j "Job Name" options

The command’s first switch is backup, which sets its mode—you cannot restore from the command line. That switch is followed by a parameter that specifies what to back up. You can specify the actual path to the local folder, network share, or file that you want to back up. Alternatively, you can indicate the path to a backup selection file (.bks file) to be used with the syntax @selectionfile.bks. The at (@) symbol must precede the name of the backup selection file. A backup selection file contains information on the files and folders you have selected for backup. You have to create the file using the graphical user interface (GUI) version of the Backup Utility.

The third switch, /J “JobName”, specifies the descriptive job name, which is used in the backup report.

You can then select from a staggering list of switches, which are grouped below based on the type of backup job you want to perform.

Backing Up to a File

Use the switch

/F “FileName”

where FileName is the logical disk path and file name. You must not use the following switches with this switch: /T /P /G.

The following example backs up the remote Data share on Server01 to a local file on the E drive:

ntbackup backup "\\server01\Data" /J "Backup of Server 01 Data folder" /F "E:\Backup.bkf"

Appending to a File or Tape

Use the switch:

/A

to perform an append operation. If appending to a tape rather than a file, you must use either /G or /T in conjunction with this switch. Cannot be used with /N or /P.

The following example backs up the remote Profiles share on Server02 and appends the set to the job created in the first example:

ntbackup backup "\\server02\Profiles" /J "Backup of Server 02 Profiles folder" /F "E:\Backup.bkf" /A

Backing Up to a New Tape or File, or Overwriting an Existing Tape

Use the switch:

/N “MediaName”

where MediaName specifies the new tape name. You must not use /A with this switch.


Backing Up to a New Tape

Use the switch

/P “PoolName”

where PoolName specifies the media pool that contains the backup media. This is usually a subpool of the backup media pool, such as 4mm DDS. You cannot use the /A, /G, /F, or /T options if you are using /P.

The following example backs up files and folders listed in the backup selection file c:\backup.bks to a tape drive:

ntbackup backup @c:\backup.bks /j "Backup Job 101" /n "Command Line Backup Job" /p "4mm DDS"

Backing Up to an Existing Tape

To specify a tape for an append or overwrite operation, you must use either the /T or /G switch along with either /A (append) or /N (overwrite). Do not use the /P switch with either /T or /G.

To specify a tape by name, use the /T switch with the following syntax:

/T “TapeName”

where TapeName specifies a valid tape in the media pool.

To back up the selection file and append it to the tape created in the previous example, you would use this command line:

ntbackup backup @c:\backup.bks /j "Backup Job 102" /a /t "Command Line Backup Job"

To specify a tape by its GUID, rather than its name, use the /G switch with the following syntax:

/G “GUIDName”

where GUIDName specifies a valid tape in the media pool.

Job Options

For each of the job types described above, you can specify additional job options using these switches:

■/M {BackupType} Specifies the backup type, which must be one of the following: normal, copy, differential, incremental, or daily.

■ /D {“SetDescription”} Specifies a label for the backup set.

■ /V:{yes/no} Verifies the data after the backup is complete.

■/R:{yes/no} Restricts access to this tape to the owner or members of the Administrators group.

■/L:{f s n} Specifies the type of log file: f=full, s=summary, n=none (no log file is created).

■ /RS:{yes/no} Backs up the migrated data files located in Remote Storage.

■ /HC:{on/off} Uses hardware compression, if available, on the tape drive.

■/SNAP:{on/off} Specifies whether the backup should use a Volume Shadow Copy.


Scheduling Backup Jobs

To schedule a backup job, create the job in the Backup Utility then click Start Backup and configure advanced backup options. After all options have been configured, click Schedule and, in the Set Account Information dialog box, type the user name and pass-word of the account to be used by the backup job.

In the Scheduled Job Options dialog box, enter a job name and click Properties. The Schedule Job dialog box appears, as shown in Below Figure. Configure the job date, time, and frequency. The Advanced button will let you configure additional schedule settings including a date range for the job. The Settings tab of the Schedule Job dialog box allows you to refine the job, for example, by specifying that the job should only take place if the machine has been idle for a period of time.

Once a job has been scheduled, you can edit the schedule by clicking the Schedule Jobs tab of the Backup Utility. Jobs are listed on a calendar. Click a job to open its schedule. Although you can also add a backup job by clicking Add Job on the Schedule Jobs tab, clicking Add Job will launch the backup wizard so that you can select the files to back up and some of the properties of the backup job. Most administrators find it more convenient to create a backup job on the Backup tab directly, then click Start Backup and Schedule, as described above.


Shadow Copies of Shared Folders

Windows Server 2003 supports another way for administrators and users alike to recover quickly from damage to files and folders. Using VSS, Windows Server 2003 automatically caches copies of files as they are modified. If a user deletes, overwrites, or makes unwanted changes to a file, you can simply restore a previous version of the file. This is a valuable feature, but is not intended to replace backups. Instead, it is designed to facilitate quick recovery from simple, day-to-day problems not recovery from significant data loss.

Enabling and Configuring Shadow Copies

The Shadow Copies feature for shared folders is not enabled by default. To enable the feature, open the Properties dialog box of a drive volume from Windows Explorer or the Disk Management snap-in. On the Shadow Copies tab, as shown in below Figure, select the volume and click Enable. Once enabled, all shared folders on the volume will be shadowed; specific shares on a volume cannot be selected. You can, however, manually initiate a shadow copy by clicking Create Now.

The default settings configure the server to make copies of shared folders at 7:00 A.M. and noon, Monday through Friday; and 10 percent of the drive space, on the same drive as the shared folder, is used to cache shadow copies.

Each of the following settings can be modified by clicking Settings on the Shadow Copies tab:

■Storage volume: To enhance performance (not redundancy), you can move the shadow storage to another volume. This must be done when no shadow copies are present. If shadow copies exist, and you want to change the storage volume, you must delete all shadow copies on the volume, then change the storage volume.

■Details: The dialog box lists shadow copies that are stored and space utilization statistics.

■Storage limits: This can be as low as 100 MB. When the shadow copy runs out of storage, it deletes older versions of files to make room for newer versions. The proper configuration of this setting depends on the total size of shared folders on a volume with shadowing enabled; the frequency with which files change, and the size of those files; and the number of previous versions you wish to retain. In any event, a maximum of 63 previous versions will be stored for any one file before the earliest version is removed from the shadow storage.

■Schedule: You can configure a schedule that reflects the work patterns of your users, ensuring that enough previous versions are available without prematurely filling the storage area and thereby forcing the removal of old versions. Remember that when a shadow copy is made, any files that have changed since the previous shadow copy are copied. If a file has been updated several times between shadow copies, those interim versions will not be available.

Using Shadow Copy

Shadow copies of shared folders allow you to access previous versions of files that the server has cached on the configured schedule. This will allow you to

■ Recover files that were accidentally deleted

■ Recover from accidentally overwriting a file

■ Compare versions of files while working

To access previous versions, click the properties of a folder or file and click the Previous Versions tab, as shown in below Figure.

The Previous Versions page will not be available if Shadow Copies is not enabled on the server, or if there are no previous versions stored on the server. It will also be unavailable if the shadow copy client has not been installed on your system. This file is located in the %Systemroot%\System32\Clients\Twclient\x86 folder of a Windows Server 2003 system. The Windows Installer (.msi) file can be deployed using Group Policy, SMS, or an e-mail message. Finally, the Previous Versions page is only available when accessing a file’s properties through a shared folder. If the file is stored on the local hard drive, you will not see the Previous Versions tab, even if the file is shared and VSS is enabled. See this lesson’s Practice for an example.

You can then choose to Restore the file to its previous location or Copy the file to a specific location.

If a file has been deleted, you obviously cannot go to the file’s Properties dialog box to locate the Previous Versions page. Instead, open the Properties of the parent folder, click the Previous Versions tab and locate a previous version of the folder that contains the file you want to recover. Click View and a folder window will open, as shown in below Figure , that displays the contents of the folder as of the time at which the shadow copy was made. Right-click the file and choose Copy, then paste it into the folder where you want the file to be recreated.

Shadow copy, as you can see, is a useful addition to the toolset for managing file servers and shared data. With VSS, you can preserve data sets at scheduled points in time. Administrators or users can then restore deleted or corrupted files, or compare files to previous versions. As the VSS cache fills, old versions are purged and new shadow copies are added.

If a user requires data to be restored and that data is no longer available through Previous Versions, you can restore the data from backup. If the server becomes corrupted, you must restore the data from backup. Although VSS enhances the manageability and resiliency of shared files, there is no substitute for a carefully planned and verified backup procedure.

Restoring Data

In conjunction with the design of a backup strategy, you must create and verify restore procedures to ensure that appropriate personnel are knowledgeable in the concepts and skills that are critical to data recovery. This topic will share the processes and options available for restoring data using the Backup Utility.


Restoring with the Backup Utility

Restoring data is a straightforward procedure. After opening the Backup Utility and clicking the Restore And Manage Media tab as shown in below Figure, you will be able to select the backup set from which to restore. Windows Server 2003 will then display the files and folders that the backup set contains by examining the backup set’s catalog. You can then select the specific files or folders you wish to restore. As with the backup selection, a blue check mark indicates that a file or folder will be fully restored. A dimmed check mark on a folder means that some, but not all, of its contents will be restored.

You are also asked to specify the restore location. For this option, you have three choices:

■Original location: Files and folders will be restored to the location from which they were backed up. The original folder structure will be maintained or, if folders were deleted, re-created.

■Alternate location: Files and folders will be restored to a folder you designate in the Alternate Location box. The original folder structure is preserved and created beneath that folder, where the designated alternate location is equivalent to the root (volume) of the backed up data. So, for example, if you backed up a folder C:\Data\Finance and you restored the folder to C:\Restore, you would find the Finance folder in C:\Restore\Data\Finance.

■Single folder: Files are restored to the folder you designate, but the folder structure is not maintained. All files are restored to a single folder.

After selecting the files to restore and the restore location, click Start Restore. Click OK and the restore process will begin. Confirm that no errors occurred.


Restore Options

Windows Server 2003 supports several options for how files in the restore location are handled during a restore. The following options are found in the Backup Utility’s Tools–Options command, on the Restore tab shown in below Figure.

■Do Not Replace The File On My Computer: This option, the default, causes the Restore utility to skip files that are already in the target location. A common scenario leading to this choice is one in which some, but not all, files have been deleted from the restore location. This option will restore such missing files with the backed-up files.

■Replace The File On Disk Only If The File On Disk Is Older: This option directs the restore process to overwrite existing files unless those files are more recent than the files in the backup set. The theory is that if a file in the target location is more recent than the backed-up copy, it is possible that the newer file contains information that you do not want to overwrite.

■Always Replace The File On My Computer: Under this restore option, all files are overwritten by their backed-up versions, regardless of whether the file is more recent than the backup. You will lose data in files that were modified since the backup date. Any files in the target location that are not in the backup set will remain, however.

After selecting files to restore, restore options and a restore destination, click Start Restore, and then confirm the restore. The Start Restore dialog box appears

Before confirming the restore, you can configure how the restore operation will treat security settings on the backed-up files by clicking Advanced in the Confirm Restore dialog box and selecting the Restore Security option. If data was backed up from, and is being restored to, an NTFS volume, the default setting will restore permissions, audit settings, and ownership information. Deselecting this option will restore the data with-out its security descriptors, and all restored files will inherit the permissions of the target restore volume or folder.

Backing Up Data

 1. Fundamentals of Backup
 2. Restoring Data
 3. Advanced Backup and Restore

Fundamentals of Backup

At the core of every backup procedure is a backup tool and a backup plan. Windows Server 2003 provides a robust, flexible utility called Ntbackup. Ntbackup supports much of the functionality found in third-party tools, including the ability to schedule backups, and interacts closely with VSS and the Removable Storage Management (RSM) system. In this topic, you will examine the conceptual and procedural issues pivotal to the backing up of data, so that you understand the fundamentals of planning for and creating backup jobs with Ntbackup.


Introducing the Backup Utility

The backup utility in Windows Server 2003, commonly referred to by its executable name, Ntbackup, can be opened by clicking Backup in the Accessories–System Tools program group in the Start menu. Alternatively, it can be launched by typing ntbackup.exe in the Run dialog box.

The first time you launch the backup utility, it runs in Wizard mode, as shown in below Figure. This topic focuses on the more commonly used Backup Utility interface. If you agree with most administrators that it is easier to use the standard utility than the wizard, clear the Always Start In Wizard Mode check box, and then click Advanced Mode.

As you can see on the utility’s Welcome tab in below Figure, you can back up data manually (the Backup tab) or using the Backup Wizard. You can also schedule unattended backup jobs. The Backup Utility is also used to restore data manually (the Restore And Manage Media tab) or using the Restore Wizard. The Automated System Recovery (ASR) Wizard, which backs up critical operating system files, will be discussed later in this book.

This topic focuses on data backup planning and execution, and to explore the capability of the Backup Utility we will use the Backup tab, as shown in below Figure, rather than the Backup Wizard.

Selecting Files to Back Up

You may use the Backup tab to select the files and folders to be backed up. Items may be on local volumes or in network folders. When you select an entire folder for backup, a blue check mark appears. If you select only certain items in a folder, the folder displays a dimmed check mark to indicate a partial backup.

To back up files or folders from remote machines, either select the items from a mapped drive or expand My Network Places. The latter is the equivalent of using a Universal Naming Convention (UNC), such as \\Server\Sharename\Path-to- resource. Although selecting files and folders through My Network Places is more cumbersome (you must navigate more levels of the interface to locate the files), it has an advantage because drive mappings are more likely to change over time than UNCs.


Selecting the Backup Destination

Windows Server 2003 allows you to create a backup job on a variety of media types: a tape drive, a removable drive such as the Iomega Jaz drive, and, most importantly, directly to file on a disk volume. If the destination is a tape, the name specified must match the name of a tape that is mounted in the tape device.

If backing up to a file, the Backup Utility creates a .bkf file in the specified location, which can be a local volume or remote folder. It is not uncommon for administrators using the Backup Utility to back up a file on each server and consolidate the resulting files on a central server, which then transfers the backups to removable media. To achieve such a consolidation, the backup destination is configured as either a UNC to a single location on a central server or a local file on each server, which is later copied to a central location.

There are two important limitations of the Backup Utility. First, it does not support writable DVD and CD formats. To work around this limitation, back up to a file, then transfer the file to CD or DVD. Second, backing up to any destination except a file requires that the target media be in a device physically attached to the system. This means, for example, that you cannot back up data to a tape drive attached to a remote server.


Determining a Backup Strategy

After selecting the files to back up and specifying the backup destination, there is at least one more critical choice to make. Click Start Backup, then click Advanced, and the Advanced Backup Options dialog box appears, allowing you to specify the backup type. The backup type determines which of your selected files is in fact transferred to the destination media.

Each backup type relates in one way or another to an attribute maintained by every file: archive. The archive (A) attribute is a flag that is set when a file has been created or changed. To reduce the size and duration of backup jobs, most backup types will only transfer to media the files that have their archive attribute set. The most common source of confusion regarding the archive attribute arises from terminology. You will frequently hear, “The file is marked as backed up,” which really means that the archive attribute is cleared after a particular backup job. The next job will not transfer that file to media. If the file is modified, however, the archive attribute will again be set, and the file will be transferred at the next backup.


Normal Backups

All selected files and folders are backed up. The archive attribute is cleared. A Normal backup does not use the archive attribute to determine which files to back up; all selected items are transferred to the destination media. Every backup strategy begins with a Normal backup that essentially creates a baseline, capturing all files in the backup job.

Normal backups are the most time-consuming and require the most storage capacity of any backup type. However, because they generate a complete backup, normal back-ups are the most efficient type from which to restore a system. You do not need to restore multiple jobs. Normal backups clear the archive attribute from all selected files.

Incremental Backups

Selected files with the archive attribute set are backed up. The archive attribute is cleared. Selected files with the archive flag are transferred to the destination media, and the flag is cleared. If you perform an incremental backup one day after a normal backup has been performed, the job will contain only the files that were created or changed during that day. Similarly, if you perform an incremental backup one day after another incremental backup, the job will contain only the files that were created or changed during that day.

Incremental backups are the fastest and smallest type of backup. However they are less efficient as a restore set, because you must restore the normal backup and then restore, in order of creation, each subsequent incremental backup.

Differential Backups

Selected files with the archive attribute set are backed up. The archive attribute is not cleared. Because a differential backup uses the archive attribute, the job includes only files that have been created or changed since the last normal or incremental backup. A differential backup does not clear the archive attribute; therefore, if you perform differential backups two days in a row, the second job will include all the files in the first backup, as well as any files that were created or changed during the second day. As a result, differential backups tend to be larger and more time-consuming than incremental backups, but less so than normal backups.

Differential backups are significantly more efficient than incremental backups as a restore set, however. To fully restore a system you would restore the normal backup and the most recent differential backup.

Copy Backups

All selected files and folders are backed up. Copy neither uses nor clears the archive attribute. Copy backups are not used for typical or scheduled backups. Instead, copy backups are useful to move data between systems or to create an archival copy of data at a point in time without disrupting standard backup procedures.

Daily Backups

All selected files and folders that have changed during the day are backed up, based on the files’ modify date. The archive attribute is neither used nor cleared. If you want to back up all files and folders that change during the day without affecting a backup schedule, use a daily backup.


Combining Backup Types

Although creating a normal backup every night ensures that a server can be restored from a single job the next day, a normal backup may take too much time to create, per-haps causing the overnight job to last well into the morning, thus disrupting performance during working hours. To create an optimal backup strategy, you must take into account the time and size of the backup job, as well as the time required to restore a system in the event of failure. Two common solutions are:

■Normal and differential backups: On Sunday a normal backup is performed, and on Monday through Friday nights, differential backups are performed. Differential backups do not clear the archive attribute, which means that each backup includes all changes since Sunday. If data becomes corrupt on Friday, you only need to restore the normal backup from Sunday and the differential backup from Thursday. This strategy takes more time to back up, particularly if data changes frequently, but is easier and faster to restore, because the backup set is on fewer disks or tapes.


■Normal and incremental backups: On Sunday a normal backup is performed, and on Monday through Friday incremental backups are performed. Incremental backups clear the archive attribute, which means that each backup includes only the files that changed since the previous backup. If data becomes corrupt on Friday, you need to restore the normal backup from Sunday and each of the incremental backups, from Monday through Friday. This strategy takes less time to back up but more time to restore.