EMC CX500I Configuration Guide - Page 46

Data Availability and Disk Space Usage, Group: RAID 5, RAID 3, RAID 1 mirrored pair

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Page 46 highlights

RAID Types and Trade-offs Data Availability and Disk Space Usage If data availability is critical and you cannot afford to wait hours to replace a disk, rebind it, make it accessible to the operating system, and load its information from backup, then use a redundant RAID Group: RAID 5, RAID 3, RAID 1 mirrored pair, or RAID 1/0. If data availability is not critical, or disk space usage is critical, bind an individual unit. A RAID 1 mirrored pair or RAID 1/0 Group provides very high data availability. They are more expensive than RAID 5 or RAID 3 Groups, since only 50 percent of the total disk capacity is available for user data, as shown in Figure 2-7 on page 2-17. A RAID 5 or RAID 3 Group provides high data availability, but requires more disks than a mirrored pair. In a RAID 5 or RAID 3 Group, the disk space available for user data is the total capacity of one less than the number of disks in the RAID Group. For example, in a five-disk RAID 5 Group, the capacity of four disks is available for user data, which is 80% of the group's total disk capacity. So RAID 5 and RAID 3 Groups use disk space much more efficiently than a mirrored pair. A RAID 5 or RAID 3 Group is usually more suitable than a RAID 1 mirrored pair for applications where high data availability, good performance, and efficient disk space usage are all of relatively equal importance. For a LUN in any RAID Group, you can provide for disaster recovery by establishing a remote mirror at a distant site. Figure 2-7 illustrates RAID type disk space usage. 2-16 EMC CLARiiON CX300, CX500, CX500i, and CX700 Storage Systems Configuration Planning Guide

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2-16
EMC CLARiiON CX300, CX500, CX500i, and CX700 Storage Systems Configuration Planning Guide
RAID Types and Trade-offs
Data Availability and Disk Space Usage
If data availability is critical and you cannot afford to wait hours to
replace a disk, rebind it, make it accessible to the operating system,
and load its information from backup, then use a redundant RAID
Group: RAID 5, RAID 3, RAID 1 mirrored pair, or RAID 1/0. If data
availability is not critical, or disk space usage is critical, bind an
individual unit.
A RAID 1 mirrored pair or RAID 1/0 Group provides very high data
availability. They are more expensive than RAID 5 or RAID 3 Groups,
since only 50 percent of the total disk capacity is available for user
data, as shown in Figure 2-7 on page 2-17.
A RAID 5 or RAID 3 Group provides high data availability, but
requires more disks than a mirrored pair. In a RAID 5 or RAID 3
Group, the disk space available for user data is the total capacity of
one less than the number of disks in the RAID Group. For example, in
a five-disk RAID 5 Group, the capacity of four disks is available for
user data, which is 80% of the group’s total disk capacity. So RAID 5
and RAID 3 Groups use disk space much more efficiently than a
mirrored pair. A RAID 5 or RAID 3 Group is usually more suitable
than a RAID 1 mirrored pair for applications where high data
availability, good performance, and efficient disk space usage are all
of relatively equal importance.
For a LUN in any RAID Group, you can provide for disaster recovery
by establishing a remote mirror at a distant site.
Figure 2-7 illustrates RAID type disk space usage.