HP BB118BV - StorageWorks Data Protector Express Package User's Manual & Technical Reference page 138

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To facilitate disaster recovery operations, Data Protector Express provides an optional disaster recovery
agent.
Access to historical files
Rotation types vary according to how much access to historical files they provide. Historical files provide
a record of the data stored on the computer or network at particular times such as the end of the week or
the end of the month.
Because the backup contains only those files present on the system at the time the backup is run, data
that was deleted since the last available historical backup will not be accounted for in the backup. For
example, suppose you maintain four sets of monthly backups to serve as historical records of your data.
You would schedule these backups to be performed on the last day of each month. Files that were created
and deleted within a month will not appear in any of the historical backups.
Different rotation types give you different levels of historical access to previous weeks, months and years.
For example, a GFS 30-tape media rotation type has eight weekly tapes, seven monthly tapes and two yearly
tapes. This provides you with historical files of at least the end of the week for the past eight weeks, the
end of the month for the past seven months and the end of the year for the past two years. On the other
hand, a Simple 4-tape media rotation type provides end-of-week and end-of-month backups in full mode of
only the last week and month.
Consider, for example, the yearly backup. Each of the three GFS default rotation types contains two
yearly backups. The first time you run one of these rotation types, you create a yearly backup. The next
yearly backup is made at the end of the current calendar year. The following year, the first media is
recycled, that is, its data is overwritten with new data and information about the files backed up in the
first year is deleted from the Data Protector Express catalog. This process continues with the second
media being recycled the following year and so on.
NOTE:
Yearly backups only provide you with access to files present on your computer or network on that one
day each year. No copy exists for files that were created after the oldest yearly backup and then deleted
before the most recent yearly backup. It is the responsibility of the user to manage the retention of media
containing critical business data.
Minimum number of tapes or media
The name of many rotation types indicates the minimum number of tape or media sets used by the
backup job. For example, the Simple 4-tape rotation type will use at least four media sets (or individual
tapes) to complete the media rotation.
NOTE:
Each media set may contain more than one tape or media. Several factors determine how much media
you will need: the type of backup being performed (for example full, differential, incremental), the amount
of data to be backed up during a full backup, and the media's storage capacity. If the total size of a full
backup is larger than the capacity of the tape, additional tapes are required. Your historical usage is the
best guide to determining how many tapes these jobs will require.
Because incremental and differential backup jobs usually back up fewer selected files than full backup
jobs, additional tapes may not be required.
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Backup Jobs
Comparing rotation types.