HP BB118BV - StorageWorks Data Protector Express Package, User Manual, Page: 183 / 365

Chapter 12: Tips, Techniques and Strategies 165
lists and opening and closing files, create network traffic and require CPU calculations. While the
location of the catalog will affect these parts of the job, the advantages of a remote location of the catalog
often outweigh any speed loss.)
Add a second device controller: A backup device and volume may be on the same machine with a local
connection between them. If the backup device and the volume share the same device controller, this
limits the speed of data transmission and may cause an error in Data Protector Express. Therefore, you
should add a second device controller specifically for the backup device. This can effectively double the
rate of data transmission and enhance operation. At the least, you should connect the backup device to a
different SCSI chain or IDE channel.
Use a wider data stream: For both network and local connections, the width of the data stream affects the
rate at which data can be transferred. Many tape drives are capable of writing data much faster than can
be transferred over older device controllers and network connections. By upgrading to more recent
technology with wider data streams, there will be fewer interruptions in the stream of data to the backup
device. For example, consider using a Wide or Ultra Wide SCSI controller for backup devices that
support such an interface. Additionally, for network connections, consider upgrading from 10Base-T
Ethernet to 100Base-TX.
Consult your manufacturer’s documentation to see if your backup device would benefit from a wider data
stream.
Use the proper number of data streams:
Data Protector Express is capable of controlling up to eight data
streams per backup device simultaneously. This feature can greatly increase your job speed since multiple
devices can simultaneously send data. For example, four backup devices can support up to 32
simultaneous data streams.
You control the data streams of a volume, directory or file from its Storage page . Normally, the Backup
stream
field on the
Storage page
of a
volume
is set to
Create new stream
, while the
Backup stream
of
a
directory
or file is set to
Use existing stream
. By changing these options, you can change the number of
backup streams, thereby affecting the speed at which the job runs. Assigning the proper number of data
streams can help speed up the data transmission rate.
In general, you should assign data streams according to the number of streams the
physical
device (e.g.,
the disk drive) is capable of handling. Usually this number is equal to the number of spindles the drive
has. Under most circumstances, you should use this number to determine the number of data streams.
One exception to this general rule is when you are working with very large files. You can increase
performance by creating an additional stream for each of these very large files. For example, if you have a
very large file with 1.0 GB or more, create a separate stream for this file. Then Data Protector Express
will be able to send the file to the tape drive at a higher rate that allows for “streaming.”
Consider these three examples:
1. A RAID device is capable of sustaining multiple data streams at once. By assigning various
directories on the RAID device to additional streams, you can increase the rate of data transmission.
To do so, assign large directories to their own streams by changing the
Backup stream
field of each
directory’s Storage page to Create new stream . Don’t add any more streams than the RAID device
can sustain.
2. On the other hand, a single physical device may have multiple logical volumes. If each volume is
assigned a separate stream, this will not result in faster data transmission and may, in fact, result in
slower data transmission if it creates additional seeks by the disk drive. To turn off one of the data
streams, change the
Backup stream field on the volume’s Storage page to Use existing stream .