Data Protection; Data Block Guard; Figure 11 Data Block Guard - Fujitsu ETERNUS AF250 Design Manual

1. Function

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 func-
tion 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, ensuring 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 duplica-
ted 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 11 Data Block Guard

User data
A0 A1
A0 CC A1
Written data
A0 CC A1
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 AF, 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 AF double-checks data by using the data block guard function and by using the supported T10-DIF
to improve reliability.
Data is protected at the SCSI level on the path to the server. Therefore, data integrity can be ensured 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.
The T10-DIF function can be used when connecting with HBAs that support T10-DIF with an FC interface.
Write
A2
1
CC A2 CC
Controller
CC: Check code
Cache memory
2
CC A2 CC
FUJITSU Storage ETERNUS AF250 S2, ETERNUS AF250 All-Flash Arrays Design Guide (Basic)
Copyright 2019 FUJITSU LIMITED
Read
User data
A0
3
A0 CC A1
2
29
A1 A2
CC A2 CC
P3AG-1822-09ENZ0