Storage Subsystem Concepts; Raid Levels - IBM DS3000 Introduction And Implementation Manual

Draft Document for Review August 30, 2007 12:59 am

4.1 Storage subsystem concepts

We need to explain some basic concepts and terms applicable to the IBM System Storage
DS3000 storage subsystem. The DS3000 is an external enclosure that provides shared
storage to the attached host servers. We can configure a large number of physical disk drives
into arrays and logical drives, and then specify which host servers can access certain logical
drives. A logical drive on the DS3000 appears as a locally attached physical disk drive to the
host server. When you configure an array, you have to specify a RAID level for this array. The
RAID level selection will depend on your particular performance and availability requirements.

4.1.1 RAID levels

DS3000 subsystems support RAID levels 0, 1, 3, 5 and 10. We describe each of these levels
in the following sections. Each different RAID level provides a different balance between
performance, data availability and usable storage capacity.
RAID 0
When you configure an array as RAID 0, the data is striped sequentially across all
participating physical drives, as shown in Figure 4-2. This RAID level can provide very fast
data access, but there is no redundancy. If a physical drive fails, the data in the array will be
lost. You should therefore not use RAID 0 for storing any critical data. A good choice for RAID
0 would be data which might require very fast access and can be easily restored. Data access
performance increases with the number of disk drives used in the array.
Figure 4-2 RAID 0
RAID 1
RAID 1 uses exactly two disk drives; all the data is mirrored between the two drives
(Figure 4-3 on page 46). All write operations are performed on both physical disks. This RAID
level provides good redundancy; in case of a disk failure, all data is still available and
7065DS3KBasicConfig.fm
Chapter 4. Basic configuration
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