ABCs of z/OS System Programming Volume 3 - IBM Redbooks

8.1 Overview of DASD types
Traditional DASD
3380 Models J, E, K
3390 Models 1, 2, 3, 9
DASD based on RAID technology and Seascape
architecture
Enterprise Storage Server (ESS)
DS6000 and DS8000 series
Figure 8-1 Overview of DASD types
Traditional DASD
In the era of traditional DASD, the hardware consisted of controllers like 3880 and 3990,
which contained the necessary intelligent functions to operate a storage subsystem. The
controllers were connected to S/390 systems through parallel or ESCON channels. Behind a
controller there were several model groups of the 3390 that contained the disk drives. Based
on the models, these disk drives had various capacities per device. Within each model group,
the various models provide either four, eight, or twelve devices. All A-units come with four
controllers, providing a total of four paths to the 3990 Storage Control. At that time, you were
not able to change the characteristics of a given DASD device.
DASD based on RAID technology
With the introduction of the RAMAC Array in 1994, IBM first introduced storage subsystems
for S/390 systems based on RAID technology. We discuss the various RAID implementations
in Figure 8-2 on page 448.
The more modern IBM DASD products, such as Enterprise Storage Server (ESS), DS6000,
DS8000, and DASD from other vendors, emulate IBM 3380 and 3390 volumes in geometry,
capacity of tracks, and number of tracks per cylinder. This emulation makes all the other
entities think they are dealing with real 3380s or 3390s. Among these entities, we have data
processing people not working directly with storage, JCL, MVS commands, open routines,
access methods, IOS, and channels. One benefit of this emulation is that it allows DASD
manufacturers to implement changes in the real disks, including the geometry of tracks and
cylinders, without affecting the way those components interface with DASD. From an
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