Lights Out Tests; Calculating Tape Retention - HP StorageWorks TL895 Tech Note

Adding the tl895 to the enterprise backup solution

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30 Adding TL895 Libraries to the Compaq Enterprise Backup Storage System

Lights Out Tests

Lights out tests were designed to consider factors that would affect backup rates when

automated tape libraries are connected to the EBS. Tape retention policies determined the

number of tapes needed to maintain several sets of backups that can be overwritten after the

retention period has expired. Full, Incremental, and Differential backups were analyzed to find

factors that would affect performance when large quantities of data were processed.

How you store the backup data on tape and how long you keep the tapes before they are erased

greatly impacts the total number of tapes needed to maintain the desired backup schedule.

Follow the procedure below to determine the amount of storage you will need.

Definition

There are three basic types of tape rotation within each backup cycle. Each method offers

advantages and disadvantages in cartridge use and restore time.

(F) Full Backups Only--All data is backed up every time a backup is conducted.

(I) Full/Incremental Backups--Each backup cycle will include one full backup and

multiple incremental backups. Incremental backups back up all data that has changed

since the last backup of any type.

(D) Full/Differential Backups--Each backup cycle will include one full backup and

multiple differential backups. Differential backups back up all the data that has changed

since the last full backup.

Procedure

1. Calculate data sets. Determine the number of full, incremental, and/or differential data

sets to be retained.

2. Assign percentages to each backup set for a given number of days. For example:

Full (F) = 100%

Incremental (I) = 20%*

Differential (D) = 20%*

*NOTE: Actual Incremental and Differential percentages vary for every backup set, based on the

actual amount of data changed.

3. Total the percentages.

4. Calculate total storage needed:

Total Percentage * Data Set (in GB) = Total Storage Needed (in GB)

5. Calculate storage capacity of each tape:

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