Hitachi STORAGE 9900 - Manual (Page 33)

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Capacities and RAID
Architecture
Storage Capacity of the Hitachi Freedom Storage ™ Lightning 9900 ™ V Series
The Lightning 9900 ™ V Series supports an unmatched range of capacities as shown
in Table 3.
Advantages of the Lightning 9900 V Series RAID Hard w a re
Hitachi designs the most advanced RAID (Redundant Array of Independent Disks)
controllers in enterprise storage to interface to its disk systems. These intelligent controllers
provide disk interface and RAID management, offloading these tasks to dedicated
processors. Each Lightning 9900 V Series ACP controller supports RAID-1+
and RAID-5 (parity RAID). All user data disks in the system are defined as part of a RAID
array of one type or another.
R A I D - 1 +
For the Lightning 9900 V Series, RAID-1+ is available in 2 Data + 2 Data and 4 Data +
4 Data disk arrangements in a RAID-1+0 configuration.
RAID-5 – Distributed Parity
RAID-5 disk arrangements for the Lightning 9900 V Series consist of four disks (3
Data and 1 Parity) of eight disks (7 Data and 1 Parity). Data is striped across RAID-5
arrays in a fashion similar to RAID-1+, but RAID-5 provides fault resilience by keeping
parity information on each stripe of data. If a failure occurs, the contents of that block can
be recreated by reading back the other blocks in the stripe along with the parity. Parity
information is distributed throughout the array to minimize potential bottlenecks in the
event of a need to rebuild data from a failed disk. The overhead of RAID-5 is equivalent to
one disk drive, regardless of the size of the array.
RAID Rebuild Capability
In the event of a disk failure, RAID-1+ or RAID-5 arrays can be rapidly and
automatically rebuilt using available “hot spare” drives. The Lightning 9900 V Series also
allows logical volumes to be expanded online. The 2D +2D RAID-1+ configuration and
3D + 1P and 7D + 1P RAID-5 configurations are shown in Figure 20.
6
System Capacities and Number of Disk Drives for Various Configurations
Raw System Raw capacity with Raw capacity with Raw capacity with
Configuration 36GB drives 73GB drives 146GB drives
Lightning 9980V ™ System
One Array Frame 9.2TB = 256 disks 18.7TB = 256 disks 37.2TB = 256 disks
Lightning 9980V System
Four Array Frames
36.6TB = 1024 disks 74.7TB = 1024 disks 149TB = 1024 disks
Lightning 9970V ™ System 4.6TB = 128 disks 9.3TB = 128 disks 18.6TB = 128 disks
RAID-1+ is unique to
Hitachi.
Intelligent controllers
offload tasks to
dedicated processors.
Table 3 – System
capacities and number
of disk drives for
various configurations.