Different types of image backups and their advantages and disadvantages


Different types of Image backup techniques in TSM

If the different variations of progressive incremental backups and file backup operations do not complete successfully or do not reach your SLA requirements, consider running an image backup to reduce the backup window. Just as we have different variations of incremental backups, we also have different types of TSM image backups.

Normal Image Backups

Image backup processing backs up your file system as a single object.

How it works ?

During image backup processing, the client sends a logical block image of a file system to the Tivoli Storage Manager server.

When to use ?
  • When you cannot resolve system memory problems or progressive incremental backup is otherwise unusable.
  • There are too many changes in the file system (greater than 1,000,000 objects) for journal-based backup.
  • Most of the file system contains small files (average size less than 1 MB).
  • You must have a faster recovery time than what can be achieved with file-level restore.
  • For AIX, HP-UX, Linux, and Solaris clients:
            - When the file system is at least 60% full.
            - Online (tdp) image backup cannot be taken, and you can unmount the file system.

Advantages
  • Backups are faster.
  • No scan time is required to determine what changed.
  • Overall data movement is faster.
  • Restore times are faster.
Disadvantages
  • You cannot restore individual files directly from the Tivoli Storage Manager server

There are 3 different variations of image backups available in TSM

Offline (static) image backup processing
  • The volumes to be backed up are mounted read-only.
  • This method is available for AIX, HP-UX, Linux x86, Solaris, and Windows operating systems.
  • This method is the most effective backup method for FlashCopy operations.
Online (dynamic) image backup processing
  • The volumes to be backed up remain online.
  • Fuzzy backup processing occurs when the data is changed during the image backup processing.
Also Read: Different types of Incremental Backups

Online image backup by using snapshots
  • The volumes to be backed up remain online.
  • The image backup is made at a single point in time.
  • It is available only for AIX JFS2, Linux x86, and Windows operating systems

Image plus incremental-by-date image backup

Image backup plus incremental-by-date image backup processing is one of two methods that you can use to run efficient incremental backups of your file system.

How it works ?

The following processes occur during image plus incremental-by-date image backup processing
  • During a full image backup (for example, when you issue the dsmc backup image command), the client sends a logical block image of a file system to the server.
  • Subsequent backups are incremental-by-date image backups (for example, when you issue the dsmc backup image -mode=incremental command), in which the client queries the server for the last backup of the entire file system.
  • The server sends the time stamp of last backup of the entire file system to the client.
  • The client scans and compares the time stamp with the local file system, and backs up the new and changed files.
During an image plus incremental-by-date restore operation, the following processes occur:
  • The client requests an incremental image restore.
  • The server sends the base image to the client.
  • The server returns more files that must be applied to the base image to satisfy the recovery point.
When to use

Run image plus incremental-by-date image backup processing in the following situations
  • You need faster backups.
  • You must be able to restore files to a specific point in time.
Periodically run full image backups to maintain a file system image that is close to what existed at the time of the last incremental-by-date image backup. When you periodically run a full image backup, it can also improve restore time.

Also Read: How to take online image backups

Advantages
  • Backups are faster.
  • No scan time is required to determine what changed.
  • Overall data movement is faster.
  • Restore times are faster.
  • Protection of files that changed after the image backup was created.
  • In some cases, recovery time and recovery point objectives are improved.
Disadvantages

Image plus incremental-by-date image backup processing has the following limitations:
  • This method reduces the flexibility of the scope of the backup operation. You must back up the entire file system.
  • The files are not backed up if the changes do not affect the date (for example, attribute, mode, ACL, rename, copy, move, and security changes).
  • The deleted files are not expired on the server.
  • Policy rebinding does not take place.
  • The entire file system must be scanned.
  • This method cannot be used if the client and server clocks are set to different times or are not in the same time zone.
  • Deleted files are not reconciled. Deleted files are not expired on the server. Therefore, when you restore an image with the incremental option, files that were deleted after the original image backup are present after the restore.
  • More storage space is required on the Tivoli Storage Manager server.

Image plus incremental backup

Image backup plus file system incremental backup processing is the second method that you can use to run efficient incremental backups of your file system.

How it works ?

The following processes during image plus incremental backup processing:
  • During a full image backup (for example, when you issue the dsmc backup image command), the client sends a logical block image of a file system to the server.
  • Subsequent backups are progressive incremental backups in which the client queries server for the active backup version metadata.
  • The server returns list of active backup versions for the entire file system.
  • The client scans and compares the list with the local file system.
  • The client backs up the new and changed files.
During an image plus progressive incremental restore operation, the following processes occur:
  • The client requests an incremental image restore.
  • The server returns the base image.
  • The server returns more files that must be applied to the base image to satisfy the recovery point.
  • The server optionally returns the list of files that must be deleted from the base image.
 When to use ?
  • When you need faster backups.
  • When you want to restore files to a specific point in time.
  • When you want to be able to reconcile deleted files.
Run incremental backups of the file system periodically to ensure that the server records additions and deletions accurately. Run an image backup periodically to ensure faster restores.




 Advantages
  • Backups are faster.
  • No scan time is required to determine what changed.
  • Overall data movement is faster.
  • Restore times are faster.
  • Protection of files that changed after the image backup was created.
  • In some cases, recovery time and recovery point objectives are improved.
 Disadvantages
  • More time is required to periodically create image backups.
  • More storage space is required on the Tivoli Storage Manager server.

Snapshot differential backup

If you are backing up NetApp filer or vFiler volumes or N-Series file server volumes, you can use a snapshot differential backup to streamline the incremental backup process.

How it works ?

The following processes occur during snapshot differential backup processing:
  • The first time that you run an incremental backup with the snapdiff option, a snapshot is created (the base snapshot) and a traditional incremental backup is run by using this snapshot as the source. The name of the snapshot that is created is recorded in the Tivoli Storage Manager database.
  • The second time an incremental backup is run with the snapdiff option, a newer snapshot is either created, or an existing one is used to find the differences between these two snapshots. The second snapshot is called diffsnapshot. The client then incrementally backs up the files that are reported as changed by NetApp to the Tivoli Storage Manager server.
When to use ?

Use this method to back up NetApp filer or vFiler volumes or N-Series file server volumes on Windows, AIX 64-bit, and Linux x86/86_64 clients.

Advantages

Snapshot differential backup processing can save you time by not having to scan the whole volume for changed files.

Disadvantages

Snapshot differential backup processing has the following limitations:
  • On Windows systems, it does not work for any of the NetApp predefined shares, including C$, because the client cannot determine their mount points programmatically.
  • You must periodically take a new base snapshot with the createnewbase option to back up any files that might have been skipped




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