Contraste de hipótesis 2

Tivoli Storage Manager exploits the multi-threading capabilities of modern operating systems by transparently initiating multiple backup or archive sessions on the client where necessary for rapid processing and data transfers between the client and the server.

The multi-session function involves three types of threads: compare, data transfer, and monitor. Compare and data threads show up as individual client sessions on the Tivoli Storage Manager server, while a monitor thread is not visible as a session.

• Compare thread

The purpose of the compare session is to generate a candidate list of files that have to be transferred to the Tivoli Storage manager server. As soon as one transaction limit is reached (see 2.3.2, “Transaction” on page 35), the list with the files for that one transaction will be handed over to a data transfer thread.

There can be one or more compare threads at the same time.

• Data transfer thread

A data transfer thread is responsible for reading the files, compressing them (if required) and sending the data and waiting for the commit from the server.

There can be one or more data transfer threads at the same time.

• Monitor thread

The task of this thread is to monitor if the overall backup or archive operation could benefit by starting more data sessions. Therefore, it is the monitor thread which decides on how many sessions are used.

Tivoli Storage

Backup-Archive client 35 In Figure 19 we can see how multiple sessions are started from the client to the server, and how they show up as individual sessions in a server query.

Figure 19. Multi-session client

The administrator and the user each have controls to influence the number of sessions that a client can start. On the server, the global setting MAXSESSIONS limits the total number of sessions of any kind which may be present. The client node setting MAXNUMMP, in its server definition, controls how many mount points (for sequential devices such as tape drives) a client may allocate. Finally, the RESOURCEUTILIZATION setting in the client option file increases or decreases the ability of the client to create multiple sessions.

2.3.2 Transaction

All data sent to Tivoli Storage Manager storage during a backup or archive session is done within the bounds of a transaction. When the client starts sending or receiving data, it pays attention to both sides of the communication (the server and the client). All operations are controlled in a such way that Tivoli Storage Manager can detect any data inconsistency during the transfer (due to a network problem, hard drive full or a file that already exists, for example). This provides a high level of data integrity for the Tivoli Storage Manager product. A single transaction is an atomic action, the smallest possible unit of work. Data sent within the bounds of a transaction is either committed completely to the system at the end of the transaction, or it is all rolled back if the transaction is ended prematurely.

Figure 20 shows an example of two backup transactions (Transaction 001 and Transaction 002) that are on their way to the server. Neither of them have

Sess Comm. Bytes Bytes Sess Platform Client Name Number Method ... Sent Recvd Type

--- --- --- --- --- --- ---1 Tcp/Ip ... 8.6 K 157Node WinNT Earth 2 Tcp/Ip 383 14.2 MNode WinNT Earth 3 Tcp/Ip 368 12.4 MNode WinNT Earth

Tivoli Storage Manager

finished yet, because the client is still sending the files related to those

transactions. As the server receives the files, it saves them in storage, but it will only commit the transaction in the server database after receiving all the

associated files.

Figure 20. Transaction processing

The size of a transaction is controlled by the server setting TXNGROUPMAX, which sets the maximum number of client files which can comprise a single transaction, and the client setting TXNBYTELIMIT which sets the maximum number of bytes that can be sent. Whichever limit is hit first as the client is sending its files, will determine the complete transaction.

2.4 Backup

Tivoli Storage Manager can perform backups of both files and raw logical volumes. When backing up files, the Tivoli Storage Manager server database keeps a list of all files and their attributes (time, date, size, access control lists, extended attributes). At each file backup operation, this list is compared to the current file system on the client workstation to determine new, deleted and changed files. Raw logical volumes are treated as separate entities and the management class policy is applied to the entire image as a whole. There is no tracking of individual files in an image backup - that is, it is treated as a separate object. More details on image or raw logical volume backup are given in 2.6,

“Logical volume backup” on page 48 File00A

Backup-Archive client 37 During backup, the client first establishes a session with the Tivoli Storage Manager server. After that, it sends the data using the transaction controls explained in 2.3.2, “Transaction” on page 35.

Tivoli Storage Manager a number of backup versions for each file or object on each client node. If and when the number of versions stored on the server exceeds the number set by the Tivoli Storage Manager administrator, older versions are deleted as newer versions are made. When you back up files, Tivoli Storage Manager also backs up all related directory information and access information. (See Figure 21.)

Figure 21. Backup in progress