Types of Backups

[Dev_T]

To understand the Types/Methods of Backup we must dive into the attributes of a file.

There are 4 basic attributes of a file which are known as DOS attributes:

READ, HIDDEN, SYSTEM and ARCHIVE

Whenever we think of Backups we must only think of the ARCHIVE attribute. 

Thumb Rule: Whenever the ARCHIVE attribute is ON (1) the file is ready for backup and whenever the ARCHIVE attribute is OFF (0) the file has been backed up.

There are 5 types of backups:

1.    Normal/Full Backup: This backup method will backup the entire selection list irrespective of the ARCHIVE BIT, but after the backup is over it will RESET the ARCHIVE bit to 0 (Change it to 0 : Meaning the file(s) has been backed up)

2.    Incremental Backup: This backup method will only backup those files on which the ARCHIVE bit is ON and after the backup is over it will RESET the ARCHIVE bit to 0 (Change it to 0 : Meaning the file(s) has been backed up)

3.    Differential Backup: This backup method will only backup those files on which the ARCHIVE bit is ON and after the backup is over it will NOT RESET the ARCHIVE bit to 0 (Keep the ARCHIVE bit as it is; that is will not mark the files as backed up) 

4.    Copy Backup: This backup method will not look at the ARCHIVE bit at all; it will simply backup the selection list without touching the ARCHIVE bit. This method is used if we need to move data from one location to another without disturbing the current backup strategy. 

5.    Daily Backup: This method works on 2 conditions; 1-Modified Date and the ARCHIVE bit. It will only backup those on which ARCHIVE bit is ON and the DATE on which the backup is taken. It will not RESET the ARCHIVE bit after the backup is over. Daily backup is rarely used if we want to move the files which are modified today and which are not yet backed up. 

Its not recomended to use Full, incremental and differential backup at the same time, we will need to either use Full+Incremental OR Full+Differential.

If we use Full+Incremental strategy, the Backups are faster, but the restore slower

If we use Full+Differential strategy, backups are slower, but the restores are faster