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62 DS8000 Series: Concepts and Architecture
4.1 Naming
It is important to understand the naming conventions used to describe DS8000 components
and constructs in order to fully appreciate the discussion of RAS concepts.
Storage complex
This term describes a group of DS8000s managed by a single Management Console. A
storage complex may consist of just a single DS8000 storage unit.
Storage unit
A storage unit consists of a single DS8000 (including expansion frames). If your organization
has one DS8000, then you have a single storage complex that contains a single storage unit.
Storage facility image
In ESS 800 terms, a storage facility image (SFI) is the entire ESS 800. In a DS8000, an SFI is
a union of two logical partitions (LPARs), one from each processor complex. Each LPAR
hosts one server. The SFI would have control of one or more device adapter pairs and two or
more disk enclosures. Sometimes an SFI might also be referred to as just a storage image.
Figure 4-1 Single image mode
In Figure 4-1 server 0 and server 1 create storage facility image 1.
Logical partitions and servers
In a DS8000, a server is effectively the software that uses a logical partition (an LPAR), and
that has access to a percentage of the memory and processor resources available on a
processor complex. At GA, this percentage will be either 50% (model 9A2) or 100% (model
921 or 922). In ESS 800 terms, a server is a cluster. So in an ESS 800 we had two servers
and one storage facility image per storage unit. However, with a DS8000 we can create
logical partitions (LPARs). This allows the creation of four servers, two on each processor
complex. One server on each processor complex is used to form a storage image. If there are
four servers, there are effectively two separate storage subsystems existing inside one
DS8000 storage unit.
server 0
Processor
complex 0
server 1
Processor
complex 1
Storage
facility
image 1
LPARs