Restoration of a small file or directory (e.g., only a few megabytes large) takes a long time from a large filesystem backup
Issue Symptoms
Restore of a small file or directory (e.g., only a few megabytes large) takes a long time from a large filesystem backup (e.g., a directory containing 1 terabyte of data).
Issue Description
Amanda stores filesystem backups in either of two general image formats:
- UNIX/Linux filesystem, NFS, and CIFS backups are tar archives, usually GNU tar.
- Windows NTFS backups are based on the ZIP64 format.
Both formats restore by starting at the beginning of the image and streaming through it serially, whether you are restoring the entire image or only selected files/directories. Therefore, the time to restore files can be similar to the time it took to create the backup image.
For restoring only selected files, tar or the Zmanda Windows Client must still stream through the entire image from beginning to end. The selected files are restored when they are found.
Resolution
To reduce the restore time for selected files, the backup time must be reduced. One way of doing this is to split the backup into multiple smaller objects that back up different parts of the original large object.
By splitting the large object into smaller ones and restoring from the smaller object, Amanda can stream through less data for the restore process.