IBM Tape Solutions for Storage Area Networks and FICON

20 IBM Tape Solutions for Storage Area Networks and FICON

The IBM 3466 Network Storage Manager provides a pre-packaged solution for implementing

backup over the LAN and getting the benefits of shared tape.

2.3 SAN backup model

In the SAN backup model (Figure 2-3), backup data is transferred across the SAN. Only

metadata is transferred across the LAN. Metadata is data about data, control information that

describes the files that are being transferred. Since the disk storage and tape storage share

the same SAN, it also becomes possible to transfer data directly between disk and tape. This

is called

server-less backup. It is also much easier for multiple servers to share a tape library

or share a pool of tape drives. These functions are considered in more detail later in this

chapter.

Figure 2-3 SAN backup model

2.3.1 LAN-free backup

Backup is traditionally done by transferring the data to be backed up over the LAN. The

advent of SANs enables data to be transferred directly over the SAN from disk storage to the

backup server and then directly over the SAN to tape.

Tivoli Storage Manager (from Version 3.7) supports a LAN-free backup mode of operation,

enhanced in Tivoli Storage Manager 4.2. A LAN-free backup is done by a backup server

using the SAN topology and functions of Fibre Channel (FC) to move the backup data over

the SAN, eliminating the LAN from the data flow.

This does two things. First, the LAN traffic is reduced. Secondly (and most importantly), the

traffic through the backup server is reduced. This traffic generally is processor-intensive

because of TCP/IP translations. With LAN-free backup, the backup server orchestrates the

data movement, manages the tape library and drives, and tells the clients what data to move.

The client is connected to the SAN. Its data can be on the SAN or the data can be on storage

directly attached to the server, as shown in Figure 2-4.

Backup

Clients

Backup

Clients

SAN

Backup

Server

LAN

Disk Pools

on the SAN

Tape Library

Chapter 2. Tape in the SAN environment 21

Figure 2-4 LAN-free backup

The LAN is still used to pass metadata back and forth between the backup server and the

client. However, the actual backup data is passed over the SAN. The metadata is the data

needed by the backup server to manage the entire backup process. It includes such things as

the file name, the file location, the date and time of the data movement, and where the new

copy resides. The metadata is small compared to the actual client data being moved.

In Step 1 of Figure 2-4, the backup server talks with the client to determine what data needs

to be moved. After the backup server determines what it wants to be done with the data, it

sends the request to the client. In this case, we show a request to move the data to the

backup disk storage pool, as may happen in a Tivoli Storage Manager environment. The

client’s own data is not part of the SAN topology in this case. Therefore, the client (in Step 2)

simply moves the data from its own disk to the backup server’s storage pool, as instructed by

the backup server.

When the move is complete, the client notifies the backup server. This reduces the system

processor overhead on the backup server dramatically. For the movement of data through the

server, about half of the server’s processing power is used to process the TCP/IP transaction.

For this example, we assume that the backup server uses its normal (non-SAN) processes of

moving the data from the storage pool to the tape. Later, we show how this is further improved

when the backup server uses the SAN directly for its own workload.

Remote Tape Library

Corporate LAN

SCSI Cables

Client

Disk

Fiber Cables

Step 2

Step

1

BackupServer

Disk Pool

Backup Server

Backup Client

SAN Topology