A dump hierarchy consists of one or more full dump levels and any incremental dump levels that you create with the bak adddump command. The dump levels define how fileset families are to be dumped; all fileset family entries in a fileset family are dumped at the same time and in the same way (fully or incrementally). A dump of a fileset family at a particular dump level produces a dump set. To create a dump set, specify the name of the fileset family and the level at which that family is to be dumped when you initiate the dump with the bak dump command. (See Backing Up and Restoring Data for a description of the bak dump command.)
A dump hierarchy is defined by the dump levels it contains. The term full dump level refers to a dump level used when creating full dumps; the term incremental dump level refers to a dump level used when creating incremental dumps; the term parent dump level refers to a dump level that serves as the reference point for an incremental dump level. Both full dump levels and incremental dump levels can serve as parent dump levels.
Each dump level in the hierarchy can be associated with an expiration date that specifies the date and time at which a tape that contains a dump set made at that level can be overwritten. Expiration dates are specified with the bak adddump or bak setexp command. A dump level's expiration date is automatically placed on a tape that contains a dump made at that level to provide an extra level of protection against accidental erasure of the information on the tape.
Whenever a tape is used, the Backup System always checks to see whether the tape already contains a dump set. If the tape contains a dump set, the Backup System overwrites the tape only with a dump set of the same name. If the Backup System determines that it can overwrite the dump set, it then determines whether an expiration date exists on the tape; if no expiration date is associated with a tape or if the expiration date associated with a tape has expired, the system overwrites the dump set on the tape with a dump set of the same name. However, if the tape's expiration date has not expired, the system refuses to overwrite the tape.
Following are some general issues to consider when building a dump hierarchy:
· A dump level can have any number of elements. The / (slash) is used as a metacharacter to separate different levels in the dump hierarchy. Regardless of its level in the dump hierarchy (full or incremental), each element in a dump level name must be preceded by a / (slash).
· Any characters can be included in a dump level name. Regular expression characters included in a name must be properly escaped with a \ (backslash) or " " (double quotes).
· Do not include a . (period) in the name of a dump level. When a dump set is transferred to tape, the last component of the dump level name becomes part of the dump set name. The elements of the dump set name (the fileset family name and the last component of the dump level name) are joined by a period. For example, if a fileset family named sys is dumped at the incremental dump level /weekly/monday, the dump set name is sys.monday.
· The maximum length for any single element in a dump level name is 28 characters. This does not include the / (slash) that precedes the element.
· The maximum length for the complete name of a dump level (full or incremental) is 256 characters. This includes any / (slashes) that are part of the name.
· A dump level is specified by its pathname. A level can share parents, but the level itself must have a unique name. Following are examples of different dump specifications:
- The /full specification defines a full dump level.
- The /full/week1 specification defines an incremental dump level, /week1, with /full as its parent.
- The /full/week1/thursday specification defines /thursday as a dump level that refers to /week1 as its parent; /week1 refers to /full as its parent.
· The dump level that you use as the parent for an incremental dump must already exist in the hierarchy when you define the incremental dump. The complete pathname of each dump level must be unique within the Backup Database of the local cell.
· A dump hierarchy can contain more than one full dump level; each level defines a separate subhierarchy in which you can create different relationships between the dump levels. The following two common methods are available to relate the incremental dumps in a subhierarchy to the full dump level and to one another:
- Each incremental dump refers to the same full dump as its parent. With this method, the dump sets created at each of the incremental levels contain all of the files in the fileset family that changed since the family was last dumped at the full level.
- Each incremental dump level (other than the first) refers to a preceding incremental dump level as its parent, rather than to the full dump level. With this method, each incremental dump includes only those files modified since a dump was last done at its parent level. When you restore files dumped in this fashion, however, you must access more tapes: the tape that contains the full dump and the tape for each incremental dump done afterward.
The two types of hierarchies can be mixed within a single subhierarchy by setting some incremental dumps to refer to the full dump level as their parent and setting others to refer to preceding incremental levels.
· There is no implied relationship between a fileset family and a dump subhierarchy; you can dump any fileset family at any level in any subhierarchy. When dumping a fileset, do not alternate between incremental dumps from different subhierarchies. To dump a fileset according to a different subhierarchy, start at the full dump level.
· Use names in the hierarchy that correspond to real-world times; these can help you remember when to create dumps at the different levels. However, the Backup System does not automatically back up filesets according to the names assigned in the dump hierarchy; it does not interpret dump level names, nor does it automatically perform an incremental dump on Thursday simply because there is a dump level called thursday.
A few general guidelines for using a dump hierarchy follow:
· To set up a group of tapes for archiving, make certain that you use unique dump names; for example, monday1, tuesday1, monday2, or tuesday2.
· To recycle tapes, use dump levels with the same name; for example, monday or tuesday.
· To archive tapes and recycle them at a later time, simply perform backups with a new set of tapes; the old set of tapes can then be archived. This creates multiple entries for the dump in the Backup Database. To restore filesets with multiple entries in the database, use the correct dump date to restore the correct information.
The Backup System prevents you from using out-of-date configuration information. For example, if a user deletes a full dump level in a hierarchy, and another user tries to start an incremental backup based on that full dump level, the incremental backup fails. The second user must view the dump hierarchy with the bak lsdumps command. This command updates the hierarchy with the most recent changes and lets the user determine another dump level to use with the command. (See Backing Up and Restoring Data for more information on the bak lsdumps command.)
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Changing a Dump Level's Expiration Date