Seagate ST39175LW Podręcznik Użytkownika Pobierz pdf (Strona 23)

Chapter 1, Introduction 13

Frozen Image Overview

The copy-on-write snapshot does not produce a copy of the source; it creates cached

copies of the blocks that have changed and a record of their location. By referring to the

snapshot, the backup process reassembles the source data on the storage device (see

Figure 4).

Figure 4. Backing up a snapshot-type frozen image

Backup is completed, now identical to

original source (see Source data at top of

Figure 3)

s1 s2 s3 s4 s5 s6 s7 s8

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

Storage device

c1 c2

Cache

At s7 and s8, snap-

shot driver tells

backup to read c1,

c2 instead of s7, s8.

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