Besides theNo media rotation option, Yosemite Server Backup provides several default media rotation types.
The rotation types vary in several ways: the number of days for which full data recovery is available, access to historical files based on backup type (full, differential, incremental, etc.), the minimum number of tapes or other media needed, and how long media is retained.
Full data recovery period
All the media rotation types provide for full data recovery in case of disaster. The full data recovery period is the number of days prior to the data loss for which every file backed up can be recovered. You will also be able to reconstruct the data for any day during that period that you ran a full backup and for which a set is available that has not been reused.
Each media rotation type provides full data recovery periods for different number of days preceding the last backup. For example, a GFS 30-tape media rotation type can reconstruct the data from any day of the past three weeks (except weekends), while a Simple 4-tape media rotation type provides for reconstruction of only the past two days.
For more information, seeComparing rotation types.
TIP:
To facilitate disaster recovery operations, Yosemite Server Backup 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
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 Yosemite Server Backup 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.
Deciding how frequently to overwrite media
Yosemite Server Backup overwrites media in two ways: by overwriting the oldest media in a rotation type, and by overwriting media on a fixed schedule based on the day of the week, month, or year. How long you retain media depends on your business needs. If you need to retain media for longer than a few days or weeks, consider using one of the fixed media rotation types. If you have a limited supply of backup media and do not need to retain media for a long time, consider the other rotation types.
Comparing rotation types
Yosemite Server Backup provides a variety of media rotation types to select from. Or, you can define your own media rotation.
The following table compares the historical backups and full data recovery capabilities of each of the rotation types provided in Yosemite Server Backup.
138 Backup Jobs
NOTE:
This table assumes that no job uses more than one media set or group and presents the default rotation type settings for the Run Repeatedly schedule type.
Table 8 Comparing rotation types Media Rotation
type Full Data Recovery
Available for Previous… Maximum Data Loss Historical backups Available for Previous…
Previous 4 weeks 1 day
Daily append Previous 3 weeks 1 day 4 weekly backups
including daily backups Custom rotation
— Fixed by day of week
Previous five business days
per set 1 day 5 daily backups per set
Custom rotation
(31 business days) 1 day 31 daily backups
Custom rotation
— Fixed by day of year
Previous 365-day year
(365 business days) 1 day 365 daily backups