Hitachi 9900 manual Capacities and RAID, Architecture, RAID-1+is unique to Hitachi

Capacities and RAID	6
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.

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

Table 3 – System capacities and number of disk drives for various configurations.

Advantages of the Lightning 9900 V Series RAID Hardware

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.

RAID-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.

Intelligent controllers offload tasks to dedicated processors.

RAID-1+ is unique to Hitachi.

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