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Chapter 5. Virtualization concepts 85
Figure 5-1 Storage Facility virtualization
5.3 The abstraction layers for disk virtualization
In this chapter, when talking about virtualization, we are talking about the process of
preparing a bunch of physical disk drives (DDMs) to be something that can be used from an
operating system, which means we are talking about the creation of LUNs.
The DS8000 is populated with switched FC-AL disk drives that are mounted in disk
enclosures. You order disk drives in groups of 16 drives of the same capacity and RPM. The
disk drives can be accessed by a pair of device adapters. Each device adapter has four paths
to the disk drives. The four paths provide two FC-AL device interfaces, each with two paths,
such that either path can be used to communicate with any disk drive on that device interface
(in other words, the paths are redundant). One device interface from each device adapter is
connected to a set of FC-AL devices such that either device adapter has access to any disk
drive through two independent switched fabrics (in other words, the device adapters and
switches are redundant).
Each device adapter has four ports and since device adapters operate in pairs, there are
eight ports or paths to the disk drives. All eight paths can operate concurrently and could
access all disk drives on the attached fabric. In normal operation, however, disk drives are
typically accessed by one device adapter. Which device adapter owns the disk is defined
during the logical configuration process. This avoids any contention between the two device
adapters for access to the disks.
RIO-G
Processor Processor
Memory Memory
I/O I/O
RIO-G
Processor Processor
Memory Memory
I/O I/O
RIO-G
Processor Processor
Memory Memory
I/O I/O
LIC LIC LIC LIC
LPAR Hypervisor
Storage Facility image 1 Storage Facility image 2
Physical
view:
physical
storage
unit
Logical
view:
virtual
Storage
Facility
images
takes part of takes part of
takes part of