Array Groups And Raid Levels - Hitachi Virtual Storage Platform User And Reference Manual

Array groups and RAID levels

The array group (also called parity group) is the basic unit of storage
capacity for the Virtual Storage Platform. Each array group is attached to
both boards of a BED pair over 16 fibre paths, which enables all data drives
in the array group to be accessed simultaneously by a BED pair. Each array
frame has two canister mounts, and each canister mount can have up to
128 physical data drives.
The Virtual Storage Platform supports the following RAID levels: RAID 10,
RAID 5, RAID 6. RAID 0 is not supported on the Virtual Storage Platform.
When configured in four-drive RAID 5 parity groups (3D+1P), ¾ of the raw
capacity is available to store user data, and ¼ of the raw capacity is used
for parity data.
RAID 10.
illustrates a sample RAID 10 (2D+2D) layout. A RAID 10 (2D+2D) array
group consists of two pairs of data drives in a mirrored configuration,
regardless of data drive capacity. A RAID 10 (4D+4D) group combines two
RAID 10 (2D+2D) groups. Data is striped to two drives and mirrored to the
other two drives. The stripe consists of two data chunks. The primary and
secondary stripes are toggled back and forth across the physical data drives
for high performance. Each data chunk consists of either eight logical tracks
(mainframe) or 768 logical blocks (open systems). A failure in a drive
causes the corresponding mirrored drive to take over for the failed drive.
Although the RAID 5 implementation is appropriate for many applications,
the RAID 10 option can be ideal for workloads with low cache-hit ratios.
Note:
recommends that both RAID 10 (2D+2D) groups within a RAID 10 (4D+4D)
group be configured under the same BED pair.
Figure 2-2 Sample RAID 10 2D + 2D Layout on page 2-3
When configuring RAID 10 (4D+4D), Hitachi Data Systems
Figure 2-2 Sample RAID 10 2D + 2D Layout
Functional and Operational Characteristics
Hitachi VSP User and Reference Guide
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