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Technique to Support both 3.5" and 2.5" SCSI Disk in Rack Optimized 1 EIA System Disclosure Number: IPCOM000125649D
Original Publication Date: 2005-Jun-09
Included in the Prior Art Database: 2005-Jun-09
Document File: 3 page(s) / 352K

Publishing Venue



Dimension of 1-EIA (Electronic Industies Alliance) rack drawer is 1.75" high x 19" wide. The depth of the 1-EIA rack drawer varies and depends on the system contents. Optional embedded hardware RAID (Redundant Array of Independent Disks) card is one of many key features in 1-EIA system. A minimum of 4 disks is needed for hardware RAID. Due to small 1-EIA volumetric space, 1-EIA system must support 2.5" SCSI disk in order to achieve up to 4 disks. However, 2.5" SCSI disk cost is approximately of 33% premium over 3.5" SCSI Disk in 2005. To be cost competitive, the 1EIA system must therefore support 3.5" in the base system configuration. This invention disclosure describes the technique to support the 3.5" disk for lowest cost in base system configuration and to accommodate the 2.5" disk for hardware RAID in 1-EIA system.

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Technique to Support both 3.5" and 2.5" SCSI Disk in Rack Optimized 1 EIA System

For cost optimized design, the SCSI susbsystem design in the 1-EIA system does not have a disk backplane. The 1-EIA system chassis has a built-in disk cage to support two 3.5" disks. Each 3.5" SCSI disk docks directly into the SCSI connector which is located on the system board. Center divider which guides the 3.5" disks docking is removeable.

The 2.5" disk feature is optional and consists of

1. One removeable 2.5" disk cage which supports four direct docking 2.5" disks and is fitted inside the built-in 3.5" disk cage.
2. An interposer assembly between the 2.5" disk and system board SCSI connector which includes two sandwitched daughter cards. The interposer assembly is fixed and tied to the 2.5" disk cage.

Before installing the 2.5" disk cage, the center divider must be removed. The 2.5" disk cage slides into the built-in 3.5" disk cage and directly docks into the system SCSI connectors. The SCSI bus, sideband signals and termination wiring are shown in the Figures below. This SCSI design supports two different SCSI topologies, maintain at Ultra320 speed and comply with Virtual SES interface for disk hot plug. Note that the on-system-board SCSI terminator is disabled when the 2.5" disk cage and its interposers installed.

SCSI Topology

2 x 3.5"DASD






Bus 1




Ultra320 Controller

SCSI Bus 0

System Board

External SCSI Port


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