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88 DS8000 Series: Concepts and Architecture
Figure 5-4 Creation of an array
So, an array is formed using one array site, and while the array could be accessed by each
adapter of the device adapter pair, it is managed by one device adapter. Which adapter and
which server manages this array is be defined later in the configuration path.
5.3.3 Ranks
In the DS8000 virtualization hierarchy there is another logical construct, a rank.
When you define a new rank, its name is chosen by the DS Storage Manager, for example,
R1, R2, or R3, and so on. You have to add an array to a rank.
The available space on each rank will be divided into
extents. The extents are the building
blocks of the logical volumes. An extent is striped across all disks of an array as shown in
Figure 5-5 on page 89 and indicated by the small squares in Figure 5-6 on page 90.
The process of forming a rank does two things:
The array is formatted for either FB (open systems) or CKD (zSeries) data. This
determines the size of the set of data contained on one disk within a stripe on the array.
The capacity of the array is subdivided into equal sized partitions, called
extents. The
extent size depends on the
extent type, FB or CKD.
An FB rank has an extent size of 1 GB (where 1 GB equals 2
30
bytes).
People who work in the zSeries environment do not deal with gigabytes, instead they think of
storage in metrics of the original 3390 volume sizes. A 3390 Model 3 is three times the size of
Array
Site
RAID
Array
Spare
Data
Data
Data
Data
Data
Data
Parity
Creation of
an array
D1 D7 D13 ...
D2 D8 D14 ...
D3 D9 D15 ...
D4 D10 D16 ...
D5 D11 P ...
D6 P D17 ...
P D12 D18 ...
Spare
Note: In the current DS8000 implementation, a rank is built using just one array.