EMC CX500I Configuration Guide - Page 45

Storage Flexibility, Certain RAID Group types - RAID 5, RAID 1,

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Storage Flexibility RAID Types and Trade-offs A RAID 1 mirrored pair has its disks locked in synchronization, but the SP can read data from the disk whose read/write heads are closer to it. Therefore, RAID 1 read performance can be twice that of an individual disk while write performance remains the same as that of an individual disk. A RAID 0 Group (nonredundant individual access array) or RAID 1/0 Group (mirrored RAID 0 Group) can have as many I/O operations occurring simultaneously as there are disks in the group. Since RAID 1/0 locks pairs of RAID 0 disks the same way as RAID 1 does, the performance of RAID 1/0 equals the number of disk pairs times the RAID 1 performance number. If you want high throughput for a specific LUN, use a RAID 1/0 or RAID 0 Group. A RAID 1/0 Group requires at least four disks; a RAID 0 Group, at least three disks. An individual unit has only one I/O operation per read or write operation. RAID types 5, 1, 1/0, and 0 allow multiple LUNs per RAID Group. If you create multiple LUNs on a RAID Group, the LUNs share the RAID Group disks, and the I/O demands of each LUN affect the I/O service time to the other LUNs. For best performance, you may want to use one LUN per RAID Group. Certain RAID Group types - RAID 5, RAID 1, RAID 1/0, and RAID 0 - let you create up to 128 LUNs in each group. This adds flexibility, particularly with large disks, since it lets you apportion LUNs of various sizes to different servers, applications, and users. Conversely, with RAID 3, there can be only one LUN per RAID Group, and the group must include five or nine disks - a sizable block of storage to devote to one server, application, or user. However, the nature of RAID 3 makes it ideal for that single-threaded type of application. RAID Benefits and Trade-offs 2-15

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RAID Benefits and Trade-offs
2-15
RAID Types and Trade-offs
A RAID 1 mirrored pair has its disks locked in synchronization, but
the SP can read data from the disk whose read/write heads are closer
to it. Therefore, RAID 1 read performance can be twice that of an
individual disk while write performance remains the same as that of
an individual disk.
A RAID 0 Group (nonredundant individual access array) or RAID
1/0 Group (mirrored RAID 0 Group) can have as many I/O
operations occurring simultaneously as there are disks in the group.
Since RAID 1/0 locks pairs of RAID 0 disks the same way as RAID 1
does, the performance of RAID 1/0 equals the number of disk pairs
times the RAID 1 performance number. If you want high throughput
for a specific LUN, use a RAID 1/0 or RAID 0 Group. A RAID 1/0
Group requires at least four disks; a RAID 0 Group, at least three
disks.
An individual unit has only one I/O operation per read or write
operation.
RAID types 5, 1, 1/0, and 0 allow multiple LUNs per RAID Group. If
you create multiple LUNs on a RAID Group, the LUNs share the
RAID Group disks, and the I/O demands of each LUN affect the I/O
service time to the other LUNs. For best performance, you may want
to use one LUN per RAID Group.
Storage Flexibility
Certain RAID Group types — RAID 5, RAID 1, RAID 1/0, and
RAID 0 — let you create up to 128 LUNs in each group. This adds
flexibility, particularly with large disks, since it lets you apportion
LUNs of various sizes to different servers, applications, and users.
Conversely, with RAID 3, there can be only one LUN per RAID
Group, and the group must include five or nine disks — a sizable
block of storage to devote to one server, application, or user.
However, the nature of RAID 3 makes it ideal for that single-threaded
type of application.