Seagate ST39175LW Instrukcja Naprawy Pobierz pdf (Strona 30)

Frozen Image Overview

16 NetBackup ServerFree Agent System Administrator’s Guide

source data until it comes to another changed block. Cache is read again as the

snapshot driver dictates. The backup, when finished, is an exact copy of the source as it

existed the moment the snapshot driver was activated.

In NetBackup ServerFree Agent, the nbu_snap and fsclone frozen image methods

provide support for copy-on-write snapshot frozen images. These are included in the Core

Frozen Image Services option.

Mirror

Unlike a copy-on-write snapshot, a mirror is a complete data copy stored on a separate

disk, physically independent of the source. Every change or write to the source data on

the primary disk is also made to the copy on the secondary disk. This creates a “mirror”

image of the source data.

As in a copy-on-write snapshot when a frozen image is required, transactions are allowed

to finish and new I/O on the primary disk is briefly halted. When the mirror image is

brought up-to-date with the source (made identical to it), the mirror is split from the

primary, meaning that new changes can be made to the primary but not to the mirror. At

this point the mirror can be backed up (see next diagram).

3 4

All data written to source

is also written to mirror

Source image

(on primary disk)

Mirror image

(on secondary)

NetBackup

client

Mirror is split from primary:

further writes to primary

are not made to mirror.

Source image

(primary)

Mirror image

(secondary)

NetBackup

client

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Seagate ST39175LW Instrukcja Naprawy Strona 30