HP B6960-96035 - Manual (Page 175)

Device sharing in SAN
Data Protector supports the SAN concept by enabling multiple systems to share
backup devices in the SAN environment. The same physical device can be accessed
from multiple systems. Thus, any system can perform a local backup on some device
or any other device. Because data is transferred over the SAN, backups do not need
any bandwidth on your conventional LAN. This type of backup is sometimes referred
to as a “LAN-free” backup. Backup performance is also improved, because
SAN-based Fibre Channel technology typically provides an order of magnitude
higher throughput than LAN technologies.
You need to prevent several computer-systems from writing to the same device at the
same time. This can become even more complex when devices are used from several
applications. Access to the devices needs to be synchronized between all systems
involved. This is done using locking mechanisms.
SAN technology provides an excellent way to manage the robotics of a library from
multiple systems. This allows the option to manage the robotics from one system
(classic) or allow each system that uses the library to access the robotics directly,
provided the requests to the robotics are synchronized between all the systems
involved.
Configuring multiple paths to physical devices
A device in a SAN environment is usually connected to several clients and can thus
be accessed through several paths, that is client names and SCSI addresses (device
files on UNIX). Data Protector can use any of these paths. You can configure all paths
to a physical device as a single logical device - multipath device.
For example, a device is connected to client1 and configured as /dev/rs1 and
/dev/rs2
, on client2 as /dev/r1s1 and on client3 as scsi1:0:1:1. Thus,
it can be accessed through four different paths: client1:/dev/rs1,
client1:/dev/rs2
, client2:/dev/r1s1 and client3:scsi1:0:1:1. A
multipath device therefore contains all four paths to this tape device.
Concepts guide 175