Sun-microsystems SUN STOREDGETM 5310 NAS Manual de usuario descargar pdf (Pagina 317)

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6-1

CHAPTER

Checkpoints/Snapshots

This chapter provides an insight on how checkpoints are created, maintained and

deleted.

6.1 Overview

The goal of the checkpoints is to minimize the number of copies when creating a

checkpoint. This document discusses what happens to a checkpoint from the time it

is created to when it is removed.

Checkpoint lifetime can be divided into three main stages: 1. Creation, 2. Active as a

pseudo filesystem, and 3. Deletion. These stages are described in the following

sections.

6.1.1 Volumes

In the operating system, every mounted file system is represented by an in-memory

data structures called fs_online. The fs_online of a volume is similar to a gate - all

accesses to the volume are routed from there. fs_online keeps information about a

volume, including the capacity, file-handle of the root directory and status flags. A

file-handle is the virtual identifier required for accessing any file system object in

system. A file-handle maintains information about the virtual volume, and the

corresponding object in that volume. In the case of checkpoint volumes, file-handles

also contain information about the checkpoint identifier (or cpid) that contains the

actual checkpointed object.

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