Veritas NetBackup™ Administrator's Guide, Volume I

Disk staging storage unit size and capacity

To take advantage of basic disk staging requires that the NetBackup administrator understand the life expectancy of the image on the Stage I storage unit.

The size and use of the file system of the Stage I storage unit directly affects the life expectancy of the image before it is copied to the Stage II storage unit. Veritas recommends a dedicated file system for each disk staging storage unit.

Consider the following example: A NetBackup administrator wants incremental backups to be available on disk for one week.

Incremental backups are done Monday through Saturday, with full backups done on Sunday. The full backups are sent directly to tape and do not use basic disk staging.

Each night's total incremental backups are sent to a disk staging storage unit and average from 300 MB to 500 MB. Occasionally a backup is 700 MB. Each following day the relocation schedule runs on the disk staging storage unit and copies the previous night's incremental backups to the final destination, a Media Manager (tape) storage unit.

The following items give more information about determining disk size for a basic disk staging storage unit.

The minimum disk size is the smallest size that is required for the successful operation of the disk staging logic.

The minimum size must be greater than or equal to the largest combined size of the backups that are placed on the storage unit between runs of the disk staging schedule. (In our example, the disk images remain on the disk for one week.)

In this example, the relocation schedule runs nightly, and the largest nightly backup is 700 MB. Veritas recommends that you double this value to allow for any problems that may occur when the relocation schedule runs. To double the value gives the administrator an extra schedule cycle (one day) to correct any problems.

To determine the minimum size for the storage unit in this example, use the following formula:

Minimum size = Max data per cycle × (1 cycle + 1 cycle for safety)

For example: 1.4 GB = 700 MB × (1+1)

The average disk size represents a good compromise between the minimum and the maximum sizes.

In this example, the average nightly backup is 400 MB and the NetBackup administrator wants to keep the images for one week.

To determine the average size for the storage unit in this example, use the following formula:

Average size = Average data per cycle × (number of cycles to keep data + 1 cycle for safety)

2.8 GB = 400 MB × (6 + 1)

The maximum disk size is the recommended size needed to accommodate a certain level of service. In this example, the level of service is that disk images remain on disk for one week.

To determine the maximum size for the storage unit in this example, use the following formula:

Maximum size = Max data per cycle × (# of cycles to keep data + 1 cycle for safety)

For example: 4.9 GB = 700 MB × (6 + 1)