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Summary



How can I manage the amount of space used by diskdirectory backups?

Resolution



It is necessary to take disk space limits into account as you set up your backup scheme. This can also assist in capacity planning for future growth of the disk storage space allotted for backups.

 

Total Quantity of Data Stored

First, determine how much data you will be backing up and how long you need to store each backup. Based on how much data is in your enterprise multiplied by the number of times the backup will run over the retention period of these backups, it is possible to determine how much space will be necessary and how many backups you will keep on the disk. Bear in mind that in a base/incremental or base/differential backup scheme, some backups will be smaller, which will affect the total amount of data backed up to disk over this time period.

 

Number of Volsers

Based on these calculations, determine the maximum number of volsers you will allocate in your DISKDIRECTORY media pool. Each backup job that runs, no matter how small it is, will use a new volser. So the number of backup instances that will run before the media expires is your minimum number of volsers to add to your DISKDIRECTORY media pools. If some backup jobs will span multiple volsers based on maximum file size (either from filesystem limits or according to the instructions below), be sure to add enough volsers for these jobs. When space is strictly limited, it may be helpful to use separate media pools for base and incremental/differential backups. There should be enough volsers in each pool for all jobs to have enough volsers to last to the end of a full cycle.

 

Capacity of Volsers

By default, the volser file will be the size of the backup, up to the size of the file system's file limit, at which point the backup will span to an additional (new) volser.

To specify the maximum size of a DISKDIRECTORY volser file, set the environment variable SSDSKMAX. This option will restrict the file size to n blocks of 32K. The following examples will result in 2GB files of 32K blocks. All DISKDIRECTORY volsers will have the same maximum size on this server.

 

  • On UNIX: Environmental variables are set in the file /opt/dpx/bin/bexenv. Add the following lines to the end to set the number of required blocks:

SSDSKMAX=62000

export SSDSKMAX

 

  • On Windows: Environmental variables are set as String Values in the Registry Editor at the following location (Data is set to the number of blocks required.)
HKEY_LOCAL_MACHINE\Software\Syncsort\BackupExpress\%servername%\0\SSDSKMAX

Example data value: 62000

Other Considerations

If the possibility of the partition filling cannot be tolerated, then the maximum capacity of the volsers should be relatively small, and the number of volsers created should be precisely calculated based on the possibility of each volser being filled to capacity. This method is best implemented with a single media pool. Volser capacity should be set as close as possible to a multiple that is reasonable for your backup data.

If a low potential for the partition to fill can be tolerated, the backup rotation can be more flexible. By defining separate media pools for large and small jobs, you can have more volsers in your enterprise and thus more backup instances. Do not add more volsers than you need for your rotation, with a few volsers allocated for unexpected data growth. The system will overwrite expired media when available before using new volsers. However, you must use your best judgment as to how much potential extra data in each job definition or media pool can be tolerated safely.

If you must keep backups longer than your disk space allows, it may be useful to periodically archive diskdirectory volsers to tape. These backups should have a retention period calculated to be long enough to stay in the catalog as long as the retention period for the diskdirectory backup. If you will be archiving volsers, ensure that there is enough temporary space available for restores needing the archived volsers.

In general, if you are archiving data for long-term storage, you will most frequently be restoring from the short-term storage on disk. When you mark the archived diskdirectory volsers as "Offsite", restores will not attempt to use these volsers unless a request for offsite media to be included in the restore is explicitly made.