Chapter 5 Basic Functions; Data Protection; Data Block Guard; Figure 5.1 Data Block Guard Function - Fujitsu ETERNUS DX80 S2 Overview

Chapter 5
Basic Functions
This chapter explains the basic functions of ETERNUS DX Disk storage systems.
5.1

Data Protection

The ETERNUS DX Disk storage system has functions to securely protect user data when an error occurs.
5.1.1

Data Block Guard

When the ETERNUS DX Disk storage system receives data from the server (when data is written from the
server), the Data Block Guard function adds eight bytes check codes to each block (every 512 bytes) of the
user data and verifies the user data at multiple checkpoints to ensure data consistency. This function can
detect a data error when data is destroyed or data corruption occurs. When the ETERNUS DX Disk storage
system sends data to the server (when data is read from the server), the check codes are removed after the
check, ensuring that data consistency is verified in the whole storage system.
If an error is detected while data is being written, the data is read again from the data that is duplicated in the
cache memory. This data is checked for consistency and then written.
If an error is detected while data is being read from a drive, the data is restored using RAID redundancy.

Figure 5.1 Data block guard function

User data
A0
A0 CC
Eight bytes check code is
appended to every 512
bytes' user data.
Written data
A0 CC
Write
A1 A2
1
A1 CC A2 CC
CC: Check Code
2
A1 CC A2 CC
ETERNUS DX80 S2/DX90 S2 Disk storage system Overview
Copyright 2013 FUJITSU LIMITED
Read
3
A0
Controller
Cache
memory
2
1
2
3
48
User data
A0 A1 A2
CC A1 CC A2 CC
Check Code append
Check Code confirmation
Check Code confirmation & removal
P3AM-4812-11ENZ0