HP B6960-96035 - Manual (Page 307)

The backup devices consist of an HP StorageWorks DLT 4115w Library as
well as two HP StorageWorks DAT24 autoloaders.
Why use the HP StorageWorks DLT 4115w Library?
The HP StorageWorks DLT 4115w Library has a single DLT4000 drive with
15 slots. It has a total compressed storage capacity of 600 GB and a maximum
sustained data transfer rate of 3 MB/s, or 10.5 GB/h, with data compression.
This is the transfer rate assumed for the remainder of this section. Currently,
the total amount of data to be backed up to the HP StorageWorks DLT 4115w
Library as a full backup, whether this is a single full backup, or the staggering
approach is used, is about 55 GB. Assuming that the size of an incremental
backup is approximately 5% of that of a full backup, a backup generation,
representing a full backup and all incremental backups based on this full
backup, requires (55+55*5%*5) GB, or 68.75 GB, of library space. In five
years time, this figure is projected to increase to about 210 GB. XYZ’s backup
policy requires that two backup generations of data be kept. Therefore, 210*2
GB, or 420 GB, of library space will be required for storage. The HP
StorageWorks DLT 4115w Library’s 600 GB storage capacity therefore
suffices.
Why use the HP StorageWorks DAT24 Autoloader?
The HP StorageWorks DAT24 autoloader has 6 24-GB data cartridges. It has
a total compressed storage capacity of 144 GB and a maximum sustained
data transfer rate of 2 MB/s, or 7 GB/h, with data compression. This is the
transfer rate assumed for the remainder of this section. Currently, the total
amount of data to be backed up to the HP StorageWorks DAT24 autoloader
connected to the aforementioned Windows 2000 client in the English
Department in a single full backup is 12 GB. Assuming that the size of an
incremental backup is approximately 5% of that of a full backup, a backup
generation, representing a full backup and all incremental backups based on
this full backup, requires (12+12*5%*5) GB, or 15 GB, of space. In five years
time, this figure is projected to increase to about 45 GB. XYZ’s backup policy
requires that two backup generations of data be kept. Therefore, 45*2 GB,
or 90 GB, of library space will be required for storage. The HP StorageWorks
DAT24 autoloader’s 144 GB storage capacity therefore suffices.
How long does a full backup last?
The Windows 2000 client in the English Department, which accounts for 12
GB of data is backed up locally to an HP StorageWorks DAT24 autoloader.
This device has a sustained data transfer rate of 2 MB/s, or approximately
7 GB/h. Therefore, a full backup of this Windows 2000 client takes about 2
hours. As the amount of data is growing at 20 to 25% per year, this client is
projected to hold about 36 GB of data in five years time. This data would
then be backed up in 6 hours.
Concepts guide 307