Data Protection; Data Block Guard; Figure 11 Data Block Guard - Fujitsu ETERNUS DX100 S4 Design Manual

2. Basic Functions

Data Protection

Data Protection

Data Block Guard

When a write request is issued by a server, the data block guard function adds check codes to all of
the data that is to be stored. The data is verified at multiple checkpoints on the transmission paths
to ensure data integrity.
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 data and verifies the data at multiple checkpoints to ensure
data consistency. This function can detect a data error when data is destroyed or data corruption
occurs. When data is read from the server, the check codes are confirmed and then removed, en-
suring that data consistency is verified in the whole storage system.
If an error is detected while data is being written to a drive, 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 redun-
dancy.

Figure 11 Data Block Guard

User data
A0 A1
A0 CC A1 CC A2 CC
CC: Check code
Written data
A0 CC A1 CC A2 CC
1. The check codes are added
2. The check codes are confirmed
3. The check codes are confirmed and removed
Also, the T10-Data Integrity Field (T10-DIF) function is supported. T10-DIF is a function that adds a
check code to data that is to be transferred between the Oracle Linux server and the ETERNUS DX,
and ensures data integrity at the SCSI level.
The server generates a check code for the user data in the host bus adapter (HBA), and verifies the
check code when reading data in order to ensure data integrity.
The ETERNUS DX double-checks data by using the data block guard function and by using the sup-
ported T10-DIF to improve reliability.
Data is protected at the SCSI level on the path to the server. Therefore, data integrity can be ensur-
ed even if data is corrupted during a check code reassignment.
By linking the Data Integrity Extensions (DIX) function of Oracle DB, data integrity can be ensured
in the entire system including the server.
Fujitsu Storage ETERNUS DX100 S4/DX200 S4, ETERNUS DX100 S3/DX200 S3 Hybrid Storage Systems Design Guide (Basic)
Write
A2
1
Controller
Cache memory
2
Copyright 2023 Fujitsu Limited
Read
User data
A0
3
A0 CC A1 CC A2 CC
2
31
A1 A2
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