Seagate ST39175LW Průvodce řešením problémů stáhnout pdf (Strana 29)

Chapter 1, Introduction 15

Frozen Image Overview

Backing up a snapshot-type frozen image

As shown in “Backing up a snapshot-type frozen image,” an accurate backup image is

obtained by combining the unchanged portions of the data with the snapshot cache.

When a backup of the snapshot frozen image begins, the backup application copies the

source data until it comes to a block that changed after the snapshot driver was

activated. The snapshot driver tells the backup process to skip that changed block and

read in its place the cached (original) copy . The backup application continues copying

When backup

completes, backup

data is identical to

original source.

s1 s2 s3 c0 s5 s6 c1 c2

s10

c1 c2 c3 c4

Source data, modified

after snapshot

s1 s2 s3 s4 s5 s6 s7 s8

s10

Backup of snapshot:

Backup reads

source data from

s0, s1, s2, s3

At s4, snapshot

driver tells backup

to read c0 instead

of s4

Next, the backup

reads s5 and s6

from the source.

Cache

s1 s2 s3 s4 s5 s6 s7 s8

s10

Backup continues

reading source or

cache, as directed

by snapshot driver.

Source

c1 c2

Cache

At s7 and s8, snap-

shot driver tells

backup to read c1,

c2 instead of s7, s8.

Backup image

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