Hp XP Continuous Access Software Bedienungsanleitung PDF herunterladen (Seite 25)

Difference Management

The differential data (updated by write I/Os during a split or suspension) between the primary

data volume and the secondary data volume is stored in each track bitmap. When a split/suspended

pair is resumed (pairresync), the primary storage system merges the primary data volume and

secondary data volume bitmaps, and the differential data is copied to the secondary data volume.

The number of bitmap areas affects the maximum possible number of pairs that can be created in

the storage system. For details on the maximum possible number of pairs, see “Maximum Number

of Pairs” (page 47).

Journal Processing

The XP Continuous Access Journal data contains the primary data volume updates and the metadata

information (associated control information), which enables the secondary storage system to

maintain update consistency of the XP Continuous Access Journal secondary data volumes. XP

Continuous Access Journal processing includes:

• Creating and storing journals at the primary storage system (see “Journal Processing at the

Primary Storage System” (page 25))

• Copying journals to the secondary storage system (see “Journal Processing at the Secondary

Storage System” (page 26))

• Storing journals at the secondary storage system (see “Storing Journals at the Secondary

Storage System” (page 26))

• Selecting and restoring journals at the secondary storage system (see “Selecting and Restoring

a Journal at the Secondary Storage System” (page 26))

• Types of journals (see “Types of Journals” (page 26)).

Journal Processing at the Primary Storage System

When a primary storage system performs an update (host-requested write I/O) on an XP Continuous

Access Journal primary data volume, the primary storage system creates the journal data to be

transferred to the secondary storage system. The journal data will be stored in the cache first, and

then in the journal volume.

Metadata information will be attached to the journal data (see “Metadata Information” (page 25)).

When the base-journal is obtained, only metadata information is created and stored in the XP

Continuous Access Journal cache or the journal volume.

Table 3 Metadata Information

DescriptionType

Type of journal (for example, base-journal or update journal)Journal type

The number of the primary data volume that stores the original dataLDEV No. (data)

The primary data volume slot number, and the start and end of the sub-block

number (data length)

Original data storing position

The volume number of the master journal volume that stores the journal dataLDEV No. (journal)

The slot number of the master journal volume, and the start sub-block numberJournal data storing position

The sequence number that is assigned when the journal is obtainedJournal sequence number

The time when the journal data is obtainedTimestamp

The journal sequence number indicates the primary data volume write sequence that the primary

storage system has created for each journal group. The journal data is transferred to the secondary

storage system asynchronously with the host I/O. The secondary storage system updates the

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