Summary
This article describes the reconstructive Catalog and reconstructive restore.
Resolution
Two types of file-level restore are allowed, normal and reconstructive. Normal restores are always allowed, while reconstructive restores require a reconstructive Catalog.
Normal Restore
In a normal restore, specific files or directories are restored. In the case of a non-empty destination directory, restores files are placed in the chosen directory.
Restore options, which are set in the management console, allow you to control behavior related to existing files:
- Skip existing files and directories
- Replace existing files
- Replace existing files and directories
- Delete existing files before restore
- Rename restored files
Other files that exist in the destination directory (files without the same name as any file being restored) are ignored. This behavior is what you would usually want when you run a restore; that is, you want to restore only the requested files and leave everything else unchanged.
Reconstructive Restore
In a reconstructive restore, a directory is restored back to the state it was in at the time of backup. In other words, if any files had been changed or added since the backup occurred, they would no longer exist in the directory following a reconstructive restore. Files that were added after the backup are deleted, because by definition, a reconstructive restore reconstructs the directory to look exactly as it did when it was backed up.
The following are example scenarios:
- Suppose that on Sunday, you run a base backup that includes FileA to FileZ on Joe's PC. On Monday, Joe deletes FileA, FileB, and FileC and creates File1, File2, and File3. On Monday night, you run an incremental backup that saves File1, File2, and File3. On Tuesday, Joe deletes FileD, FileE, and FileF and creates File4, File5, and File6. On Tuesday night, you run another incremental. On Thursday, Joe makes numerous mistakes while editing and wants to restore his system to the way it was on Wednesday.
If reconstructive restore is on, you can click on Reconstructive Restore and enter the desired day and time. Joe's system will be restored to the way it looked on Wednesday. It will not contain the deleted files A-F. It would contain the newly created files 1-6. If reconstructive restore were off, you would restore both the deleted files A-F and the new files 1-6. - Continuing with the same example, suppose the incremental backups are run at 1:00 p.m. instead of at night. On Thursday morning, Joe creates File7, File8, and File9. On Thursday at 3:00 p.m., after the daily incremental has run, Joe decides to restore his system to the way it was on Wednesday. In this case, if reconstructive restore were enabled, you would get the same results as before. But Backup Express would erase File7, File8, and File9 since they did not exist on Wednesday. If reconstructive restore were off, File7, File8, and File9 would remain.
Need for a Reconstructive Catalog
Normal and reconstructive restores satisfy two different needs. When you enable a reconstructive Catalog (that is, a Catalog capable of supporting reconstructive restores), the restore window of the management console displays a check box to indicate whether or not the restore should be reconstructive. This can be decided on a case-by-case basis, differently for each restore job.
Understand the difference between a reconstructive Catalog and a reconstructive restore. A reconstructive Catalog allows the choice of performing either a normal or a reconstructive restore. A non-reconstructive Catalog only allows for normal restores.
Overhead for a Reconstructive Catalog
A reconstructive Catalog adds considerable overhead. Every backup, including incremental and differential backups, must save a copy of the entire directory in addition to the backed up files. Incremental and differential backups are an important distinction here, since they only back up the files that have changed or been added. For a reconstructive Catalog, the entire directory must be copied so that the Catalog can track which files have been deleted and, if requested, can restore the directory to its state at the time of the incremental or differential backup. Reconstructive Catalog must be explicitly enabled. You want to avoid the overhead of reconstructive Catalog if you will never need to run a reconstructive restore.
Note: Reconstructive restore is not supported and will not work for all versions of Novell Netware and Linux OES platforms, due to the use of TSAs in the backup/restore process.