IBM Tape Solutions for Storage Area Networks and FICON

22 IBM Tape Solutions for Storage Area Networks and FICON

2.3.2 Server-free backup

Server-free (or server-less) backup refers to the ability to take a snapshot of the data to be

backed up with minimal or no disruption to productive work, and then move it intelligently

between tape and disk without the data going through a server. Figure 2-5 shows this type of

backup.

All the elements to achieve this backup are available. Currently several software solutions are

available. The key elements are:

򐂰 Creating an instant copy: This can be done either by host-based software or by copy

functions in the disk storage server itself, such as FlashCopy® in the IBM TotalStorage®

Enterprise Storage Server® (ESS) or the Modular Storage Server (MSS).

򐂰 Mapping physical blocks to logical files: The physical data blocks must be mapped to

the file system or database and the mapping process managed.

򐂰 Moving the data directly between the disk and tape: This is done using the SCSI

extended copy command. The component that performs the SCSI commands can

theoretically be in one of the SAN fabric components. Or it can be software that runs on a

server.

Current implementations of server-free backup, such as Tivoli Storage Manager (from Version

5.1), Legato Celestra Power and Veritas NetBackup, manage the whole process by software.

Figure 2-5 Server-free backup

2.4 Sharing and pooling

Library sharing has been practiced for some time by partitioning a physical library into

multiple logical libraries. Alternatively, the library can appear to be shared by multiple hosts

when, in reality, one of the hosts (the library manager) is issuing all the library commands

Tape Library

LAN

SAN

Backup Server

Backup Client

Device-to-device

data movement

Disk Pool

Active

data

Flash

copy

Chapter 2. Tape in the SAN environment 23

both for itself and for the other hosts (clients), but all of them have direct access to the tape

drives (tape pooling).

At this point, we need to clarify the terms homogeneous and heterogeneous, as they apply to

library sharing. The terms refer to the library management or backup software, not to the

platforms on which they are running.

For example, the IBM Tivoli Storage Manager library manager may be running on an IBM

Eserver xSeries®, and several Tivoli Storage Manager clients may be running on a mixture

of HP-UX, Sun Solaris, and Windows NT servers. This is still a homogeneous environment,

because Tivoli Storage Manager is the only application using the library although the other

hosts may be sending data directly to the tape drives.

We have a heterogeneous environment when different software applications access the

library, in which case, there is no master control. Therefore, the library needs to be logically

partitioned or have its own in-built library manager, such as in the IBM 3494. Table 2-1 shows

the relationship between homogeneous and heterogeneous applications with respect to

library and drive sharing.

Table 2-1 Library and drive: Partitioning versus sharing

Prior to SAN, sharing single-path libraries was quite difficult due to the physical restrictions of

attaching multiple hosts to the library controller. However, with SAN, all hosts now have

access to all devices including the library controller. Figure 2-6 shows the relationships

between single path and multipath libraries, and library and robotic sharing.

Figure 2-6 Single-path and multipath sharing

Tape library sharing Tape drive sharing

Homogeneous

application sharing

Solved by backup application

(ARCserve, Tivoli Storage Manager)

OR by tape library hardware

partitioning (IBM 3584, 3575, or 3494)

Solved by backup application

(such as CA ARCserve or Tivoli

Storage Manager)

Heterogeneous

application sharing

Solved by Library Management

Middleware OR by tape library

hardware partitioning (IBM 3584, 3575,

or 3494)

Solved by Library Management

Middleware (such as Veritas

Media Librarian, or Legato

SmartMedia)

Tape Library/Robotic Sharing

Single Path (3583)

Homogeneous application

- TSM (AIX, NT, Sun)

- ISV

MultiPath (3584, 3575)

Single Logical Library

Homogeneous application

- TSM (AIX, NT, SUN)

- BRMS (OS/400)

- ISV

Multiple Logical Libraries

Heterogeneous application

- TSM (any platform)

- BRMS (OS/400)

- ISV