User guide

Hardware architecture 2–9
Hitachi Unified Storage VM Block Module Hardware User Guide
parity tracks are mapped to specific physical drive locations within each
array group. Therefore, each track of an LDEV occupies the same relative
physical location within each array group in the storage system.
In a RAID-6 (dual parity) configuration, two parity drives are used to
prevent loss of data in the unlikely event of a second failure during a rebuild
of a previous failure.
LDEV striping across array groups
In addition to the conventional concatenation of RAID 1 array groups
(4D+4D), the HUS VM supports LDEV striping across multiple RAID 5 array
groups for improved logical unit performance in open-system
environments. The advantages of LDEV striping are:
• Improved performance, especially of an individual logical unit, due to an
increase in the number of data drives that constitute an array group.
• Better workload distribution: in the case where the workload of one
array group is higher than another array group, you can distribute the
workload by combining the array groups, thereby reducing the total
workload concentrated on each specific array group.
The supported LDEV striping configurations are:
• LDEV striping across two RAID 5 (7D+1P) array groups. The maximum
number of LDEVs in this configuration is 1000. See the following figure.
• LDEV striping across four RAID 5 (7D+1P) array groups. The maximum
number of LDEVs in this configuration is 2000. See Figure 2-5: LDEV
Striping Across 4 RAID 5 (7D+1P) Array Groups on page 2-10.
Figure 2-4: LDEV Striping Across 2 RAID 5 (7D+1P) Array Groups