HP B6960-96035 manual Device sharing in SAN, Configuring multiple paths to physical devices

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.

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