Hitachi 9900 Series - Manual (Page 32)

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Capacities and RAID
Architecture
Storage Capacity of the Lightning 9900 ™ Series
The Lightning 9900 ™ 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 18GB drives 73GB drives 180GB drives
Lightning 9960
One Array Frame
1.7TBs = 96 disks 7.0TB = 96 disks 16.6TB = 96 disks
Lightning 9960
Six Array Frames
9.4TB = 512 disks 37.4TB = 512 disks 88.3TB = 512 disks
Lightning 9910 .9TB = 48 disks 3.5TB = 48 disks 8.3TB = 48 disks
Advantages of the Lightning 9900 ™ Series RAID Hardware
Hitachi designs the most advanced RAID (Redundant Array of Independent Disks)
controllers in enterprise storage to interface to its disk subsystems. These intelligent
controllers provide disk interface and RAID management, offloading these tasks to
dedicated processors. Each Lightning 9900
™ Series ACP controller supports RAID-1+
and RAID-5 (parity RAID). All disks in the system are defined as part of a RAID array
of one type or another. Non-volatile RAM on each controller accelerates RAID functions,
particularly disk writes.
RAID-1+
With the announcement of the Lightning 9900 Series RAID-1+ was introduced.
RAID-1+ is a 2 Data + 2 Data disk arrangement (four disks total) in a RAID-1+0
configuration with a twist – a rotating copy.
RAID-5 – Distributed Parity
RAID-5 arrays consist of four disks. 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 ™ also allows
logical volumes to be expanded online. Configurations for RAID-1+ and RAID-5 are
shown in Figure 20.
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Table 3 – System
capacities and number
of disk drives for various
configurations.
Intelligent controllers
offload tasks to
dedicated processors.
RAID-1+ is unique to
Hitachi.