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 Open
File Backup (OFB) is a utility that helps GBM capture files that
are open, even if they are changing during the backup, without
locking users out of the applications or forcing them to log off
the network.
File Access Manager monitors the file system for read requests
coming from GBM. When the backup operation is initiated, FAM
determines a point in time when there are no partial transactions
pending on the system. Once it discovers this state, it begins
maintaining a dynamically allocated pre-write cache for each open
file on the system; this is called Preview Data.
From this point on, any file modification goes directly to the
intended file ― after File Access Manager has placed a copy of the
data to be overwritten into the Preview Data. When GBM gets to a
part of a file that has been changed during the backup, FAM
substitutes the original, pre-write Preview Data to fulfill the
backup request.
The file on the backup destination will then be identical to what
was on the disk when the backup application first began backing up
the system. Meanwhile, users of the data have normal read and
write access to their files.
File Access Manager does not add any noticeable systems overhead.
The speed of the backup will not be affected by using FAM. If
backup time increases it is because more files are being copied
that were previously skipped, which is the main reason for using
FAM.
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