Operations
54
Various Functions
RAID functions
The unit provides RAID functions for the purpose of improving the reliability and availability.
The fault tolerance for the protection of data is different when writing and reading. RAID levels for each write and
read are listed in the following table.
≥
With this unit, the RAID configuration of each 3.6 TB magazine consists of top and bottom sides of 6 discs (12
sides in total). The RAID configuration of each 1.2 TB magazine consists of 12 discs (12 layers). The 12 layers
that make up the RAID in each magazine is called a “RAID configuration unit”.
≥
RAID 5 or 6 for write fault tolerance can be set from the application. In the factory default settings, the write
operation is enabled when the number of drive failure*
1
is 0 for RAID 5, the number of drive failure is 1 for RAID 6.
For more information about the settings, refer to the user manual for the application.
≥
The maximum transfer rate and the RAID configuration unit capacity for writing are different depending on the
RAID level settings. For the maximum transfer rate and capacity for each RAID level, refer to “Specifications”
(
84).
*1
The number of writing/reading sides in drive systems that cannot perform reading/writing due to such reasons as
drive failures*
4
, damaged media inside magazines, the lack of space available for management information, and
access to low redundancy areas.
*2
The number of writable drive failures can be set to 0 or 1 in the application.
*3
The number of writable drive failures can be set to 0, 1 or 2 in the application.
*4
It is not possible to write/read data to/from two sides of 3.6 TB magazines in the event of a drive failure.
RAID Level
RAID 0
RAID 5
RAID 6
Fault tolerance in
write
performance
Number of
drive failure = 1
Writable*
2
/
Warning report
Writable*
3
/
Warning report
Number of
drive failure = 2
No write/Error report
Number of drive
failure
S
3
Fault tolerance in
read
performance
Number of
drive failure = 1
Readable/Warning report
Number of
drive failure = 2
No read/Error report
Number of drive
failure
S
3
Note
In order to improve reliability and availability, RAID 5 or 6 is recommended.