Planning Your Ds Storage Structure - IBM Midrange System DS4000 Series Hardware Manual

4.1 Planning your DS storage structure

Planning the details of the configuration of your DS Storage System is the key to a successful
implementation. We cover in this section the different alternatives available to configure your
system.
4.1.1 DS5000 arrays and RAID levels
An array is a set of drives that the system logically groups together to provide one or more
logical drives to an application host or cluster.
When defining arrays, you often have to compromise among capacity, performance, and
redundancy.
RAID levels
We go through the different RAID levels and explain why we choose a particular setting in a
particular situation, and then you can draw your own conclusions.
RAID 0: For performance, but generally not recommended
RAID 0 (Figure 4-1) is also known as
requiring rapid loading of large tables, or more generally, applications requiring fast access to
read-only data or fast writing. RAID 0 is only designed to increase performance. There is no
redundancy, so any disk failures require reloading from backups. Select RAID 0 for
applications that will benefit from the increased performance capabilities of this RAID level.
Never use this level for critical applications that require high availability.
Figure 4-1 RAID 0
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IBM Midrange System Storage Hardware Guide
Disk 1
Actual
Block 0
device
Block 3
mappings
etc.
data striping
. It is well-suited for program libraries
Logical Drive
Block 0
Block 1
Block 2
Host view
Block 3
Block 4
Block 5
etc.
Disk 2
Block 1
Block 4
etc.
Stripeset
Disk 3
Block 2
Block 5
etc.