How open file and manager work together
1. Open File Manager monitors the file system for read requests coming from the backup
program. When the backup application accesses the first file for backup, Open File Manager
determines when there are no partial transactions pending.
2. When it discovers this state, it then begins maintaining Preview Data in a dynamically
allocated Pre-Write Cache for all open files on the system. The cache is in the form of
standard disk files and is distributed across all volumes in order to reduce the load on any
one volume. It grows and shrinks dynamically, so that the system administrator isn’t required
to pre-allocate the peak usage cache space. In comparison, other backup programs have a
cache that is limited to a single volume. If the cache grows too large for one volume, or if the
administrator doesn’t pre-allocate enough space, the operation will fail.
During this time, Open File Manager is constantly monitoring the file system for read requests
coming from the backup program.
3. When the application reaches a part of a file that has been changed, Open File Manager
substitutes the original (pre-write) data from the Pre-Write Cache to fulfill the backup request.
As the backup progresses, any file-write operation from another application goes directly to the
proper file, while a copy of the Preview Data (the data that will be overwritten) is placed by Open
File Manager into the Pre-Write Cache. When the backup program reaches a part of the file that
has been changed during the backup of that file, Open File Manager then substitutes the original
Open File Manager White Paper