WO1993022729A1

WO1993022729A1 - Configurable split scsi system

Info

Publication number: WO1993022729A1
Application number: PCT/US1993/003798
Authority: WO
Inventors: Rueben M. Martinez; Mark Lewis
Original assignee: Digital Equipment Corporation
Priority date: 1992-04-27
Filing date: 1993-04-21
Publication date: 1993-11-11

Abstract

A SCSI system for structuring the configuration of mass storage devices includes a SCSI backplane (16) having connectors (18a-18g) that each receive a mass storage device. The backplane connectors are connected together to form different SCSI buses. A jumper (22) configures selected ones of the different SCSI buses to form a common SCSI bus. A termination board (24a) isolates each separate SCSI bus from other SCSI buses.

Description

CONFIGDRABLS SPLIT SCSI SYSTEM

FIELD OF THE INVENTION

The present invention relates to systems for managing and controlling access to disk drives in data processing systems. More particularly, the present invention relates co a Small Computer System Interconnect ("SCSI") system that may be configured to accommodate a variety of. multiple disk drive arrangements.

BACKGRO UND OF THE INVENTION

Conventional assemblies for holding disk drives house either a single or multiple disk drives of a predetermined form factor. As information storage needs have continued to grow, many methods of configuring multiple disk drives to operate as a single unit have evolved. The

configuration of multiple disk drives as a single unit achieves many desirable goals, such as providing redundant storage (back-up) capacity in the event that one or more individual disk drives becomes inoperable or otherwise requires service. One commonly known strategy to configure multiple disk drives is referred to as redundant arrays of inexpensive disk drives ("RAID"). Using RAID, multiple disk drives are configured so that the information stored on any single disk drive is also redundantly stored on at least one of the other disk drives. In this manner, all information stored on a disk drive system may be accessed even if one or more of the individual disk drives is inoperative.

In a typical RAID system, a common SCSI backplane with multiple connectors is employed to support the operation of several disk drives. RAID is flexible enough

to support many physical configurations of disk drives. For example, there is no predetermined number of disk drives that must be employed in a RAID system, in fact, one of the advantages of RAID is that it allows users to add additional disk drives to their systems over a period of time.

As will be appreciated by those of ordinary -skill in the field, a typical RAID system includes at least five

SCSI buses having at least one disk drive associated with each SCSI bus. The disk drives are configured in "ranks" by software in a RAID controller. A rank must be

configured to include at least one disk drive from each of five separate system SCSI buses. More than one disk drive from each of the five system SCSI buses may be configured as part of a rank, and the number of disk drives from each SCSI bus does not have to be equal. For example, a rank may configured to include the following: one disk drive from SCSI bus one; two disk drives from SCSI bus two; one disk drive from SCSI bus three; three disk drives from SCS bus four; and two disk drives from SCSI bus five. A sixth SCSI bus may be employed to support a spare disk drive for each rank.

The number of ranks that may be configured in a RAID system ranges from one to six. There is no standard number of ranks. Similarly, there is no standard number of disk drives in a rank. Rather, the size of each rank is a function of the need of individual system users, limited only by the ability of the specific host system to access the desired amount of memory. The addition of auxiliary ranks to a system or auxiliary disk drives to a rank adds to the amount of storage space available on the system, but is otherwise transparent to the system user.

When new disk drives are added to a system, the SCSI configuration of the backplane may require modification. For example, it may be desirable to reconfigure a

single-bus SCSI system into a dual-bus SCSI system, or vice-versa. To facilitate this capability, a SCSI system that is easily reconfigured by a user in the field to support a variety of physical arrangements of multiple disk drives is desirable.

A configurable SCSI system would facilitate the use of a single SCSI backplane connector design capable of

supporting a number of RAID system 10 configurations. The configurable SCSI system would reduce manufacturing cost by eliminating the need for multiple SCSI backplane connector designs. SUMMARY OF THE INV ENTION

The present invention facilitates the use of disk drive systems in which multiple disk drives are associated with one another to provide additional storage space. A user of such a system is provided with the capability to add auxiliary ranks of storage in modular fashion by reconfiguring the structure of existing system SCSI buses. The addition of auxiliary ranks is made easy so that adding auxiliary ranks or auxiliary disk drives to existing ranks can be performed by the user of the system without the need to resort to hiring an electrical technician or other computer professional.

A SCSI backplane having a predetermined number of connectors is configured so that connector pins on specific ones of the connectors are connected together in parallel to correspondingly provide individual SCSI buses. A

different disk drive can be connected to each separate backplane connector so the amount of storage space in a given rank can be altered by configuring more than one disk drive from a given SCSI bus in a rank.

Jumpers are provided to allow the predefined backplane SCSI buses to be connected in series with each other to form larger buses having more connectors. In this manner, the separate SCSI buses may be jumpered together to form larger RAID ranks. Termination boards are used to

effectively isolate connectors that are associated with different SCSI buses. Thus, the present invention allows the user to install jumper plugs and termination boards on the SCSI backplane to effectively control: (1) the number of ranks in the system; and (2) the amount of storage space associated with each SCSI bus (the number of connectors assigned to each SCSI bus).

The present invention can be used to configure disk drives systems in original equipment manufacture or to modify equipment already in the field.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a multiple disk drive housing of the type suitable for use with the configurable split SCSI system of the present invention;

FIG. 2 is a cut away view of the housing of the assembly of FIG. 1 showing a simplified representation of a SCSI backplane connector;

FIGs. 3-4 are simplified schematic diagrams showing one embodiment of the configurable split SCSI system of the present invention;

FIGs. 5-6 are simplified schematic diagrams showing another embodiment of the configurable split SCSI system of the present invention.

While the invention is susceptible to various

modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. On the contrary, the applicant's intention is to cover all

modifications, equivalents, and alternatives falling within e spirit and scope of the invention as defined by the appended claims. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention facilitates the use of disk drive systems in which multiple disk drives are associated with one another to provide additional storage space or other capabilities. A known strategy for accomplishing this purpose is to replace a single disk drive with a housing containing a redundant array of inexpensive disk drives ("RAID") in data processing systems such as a standard personal computer ("PC"). For purposes of clarity, the examples of the configurable split SCSI system of the present invention are described with reference to a RAID system. It will be appreciated by one of ordinary skill in the field that the present invention is equally applicable to any methodology of configuring multiple disk drives or other mass storage devices.

Referring to the drawings, wherein the reference characters designate like or corresponding parts throughout the views, FIG. 1 is a perspective view of a multiple disk drive system 10 of the type suitable for use with the configurable split SCSI system of the present invention. A housing 11 is adapted to accommodate a plurality of mounting units 12a-12g. Each of the mounting units 12a-12g secures a separate disk drive or other mass storage device in the housing 11. The mounting units 12a-12g are

separately releasable from the housing 11. A SCSI

backplane connector (see FIG. 2) is adapted to engage each of the disk drives to allow the disk drives to be accessed by a host computer.

FIG. 2 is a cut away view of the housing 11 of the assembly of FIG. 1 showing a simplified representation of a SCSI backplane 16 having a plurality of SCSI connectors

18a-18g. Each of the SCSI connectors 18a-18g receives an associated connector from the disk drive in one of the mounting units 12a-12g. The pin configuration of the SCSI connectors 18a-18g may be of any known design. The

specific pin configuration is not an essential feature of the present invention.

As will be appreciated by those of ordinary skill in the field, various known SCSI backplanes are designed so that certain specific connectors are electrically connected to form distinct SCSI buses on the backplane. FIGs. 3-4 are simplified schematic diagrams showing one embodiment of the configurable split SCSI system of the present

invention.

Fig. 3 shows a SCSI backplane 16 in which connectors 18a, 18b and 18c are permanently connected together in series to form one SCSI bus B1 and connectors 18d, 18e, 18f and 18g are connected to form a second SCSI bus B0. This structure allows more than one individual disk drive to be connected on a single SCSI bus.

In FIG. 3, the SCSI backplane 16 supports two SCSI busses: B0 and B1. As previously noted, a rank in a RAID system requires at least one disk drive on each of five separate SCSI buses. Therefore, the SCSI backplane 16 depicted in FIG. 3 must be associated with at least two other SCSI backplanes (assuming the additional backplanes have the same .configuration as the backplane 16) to form a single RAID rank. The backplane configuration shown in FIG 3 supports four disk drives on SCSI bus B0 (identified as 1, 3, 5 and 6) and three disk drives on SCSI bus B1

(identified as disk drives 0, 2 and 4). Termination boards 24a and 24b of the type commonly known in the art are installed at the end of the SCSI bus B0 and the SCSI bus B1, respectively, to ensure isolation between the buses.

Because the number of connectors on a single SCSI bus and the number of RAID ranks are not standardized,

individual system users are able to configure systems having as many (or as few) RAID ranks as their individual needs dictate. The configurable split SCSI system of the present invention provides system users with increased flexibility to configure their systems according to their own needs by allowing separate SCSI buses on backplanes to be connected to form larger individual SCSI buses.

Individual system users may join connectors together to form a SCSI bus having more connectors. As previously noted, the configuration of disk drives on the same SCSI bus into ranks is accomplished by the programming of a RAID disk drive controller. Such controllers are known to those having ordinary skill in the field and do not constitute an essential feature of the present invention.

In FIG. 4, the present invention allows the system user to create a single SCSI bus B0 to be formed by joining the connectors 18a, 18b and 18c (SCSI bus B1 in FIG. 3) with a jumper 22 to the connectors 18d, 18e, 18f and 18g (SCSI bus B0 in FIG. 3). The specific features of the jumper 22 are commonly known and are not

an essential feature of the invention. Generally, the jumper 22 connects corresponding pins on different SCSI connectors together. In this manner, the number of SCSI buses on the SCSI backplane 16 is reduced from two (FIG. 3) to one (FIG. 4), but the resulting extended SCSI bus B0

(FIG. 4) is capable of supporting seven disk drives, which may be configured by the programming of a RAID disk drive controller in any number of ranks between one and seven. A termination board 24c is connected to the end of the SCSI bus B0 to isolate it from other SCSI buses.

Another benefit of the present invention is that it allows distinct SCSI backplanes to be connected together in conjunction with each other to form extended SCSI buses. This feature allows the system user to expand the number of RAID ranks or the number of disk drives associated with each separate SCSI bus in modular fashion (i.e. by

associating connectors on different SCSI backplanes with each other). FIGs. 5 and 6 are simplified schematic diagrams showing another embodiment of the configurable split SCSI system of the present invention. As shown in FIG. 5, a SCSI backplane 16 includes six individual connectors

18a-18f. The connectors 18a-18f correspond to separate SCSI buses B0-B5. Termination boards 24a-24f are installed at the ends of the SCSI buses B0-B5,

respectively, to isolate the SCSI buses B0-B5 from each other. Thus, the SCSI backplane configuration shown in FIG. 5 supports six separate SCSI buses. Accordingly, the backplane configuration shown in FIG. 5 can support one complete RAID rank, including a spare SCSI bus.

In FIG. 6, a combination of jumpers 22a-22c and termination boards 24a-24c are installed as shown on the SCSI backplane 16 to configure the backplane to support three distinct SCSI buses B0-B2, each having two separate disk drive connectors associated therewith. Therefore, an additional SCSI backplane identical to the backplane shown in FIG. 6 is needed to support five separate SCSI buses required to configure a RAID unit. Unlike the backplane configuration shown in FIG. 5, the configuration shown in FIG. 6 supports two RAID ranks (one disk drive per rank). Termination boards 24a-24c are connected to the ends of SCSI buses B0-S2, respectively, to isolate the SCSI buses B0-B2 from each other.

It should be noted that the present invention

facilitates the easy transformation from a RAID system that supports a single rank (FIG. 5) to a system that supports two ranks. In addition to providing enough SCSI buses to support RAID, the use of another SCSI backplane having the same configuration as the SCSI backplane (FIG. 5) would provide a sixth SCSI bus to support a spare disk drive for each rank.

Thus, there has been described herein a configurable split SCSI system that allows flexible configuration of disk drives in multiple disk drive applications. It will be understood that various changes in the details,

arrangements and configurations of the parts and system which have been described and illustrated above in order to explain the nature of the present invention may be made by those skilled in the art within the principle and scope of the present invention as expressed in the appended claims.

Claims

What is claimed is: 1. A Small Computer System Interconnect (SCSI) system having a configurable backplane for receiving a plurality of mass storage devices, comprising:

a SCSI backplane (16) having a plurality of connectors (18a-18g), each of said connectors including means for receiving one of the plurality of mass storage devices and connecting the device to a SCSI bus, each of said

connectors corresponding to one of a plurality of separate SCSI buses;

at least one jumper (22) for connecting a first one of said connectors to a second one of said connectors for configuring the mass storage device received by said first one of said connectors and the mass storage device received by said second one of said connectors on a common SCSI bus; and

at least one termination board (24a) connected to each of said plurality of SCSI buses to isolate each of said plurality of SCSI buses from every other one of said plurality of SCSI buses.

2. The SCSI system of claim 1, further comprising means for connecting additional SCSI backplanes with said SCSI backplane so that at least five SCSI buses exist and said plurality of mass storage devices are configured in a RAID system.

3. A SCSI system having a configurable backplane for receiving a plurality of mass storage devices, comprising: a SCSI backplane (16) having a plurality of connectors (18a-18g), each of said connectors including means for receiving one of the mass storage devices, a first selected group of said connectors being linked to connect the mass storage devices associated with said first selected group of said connectors to form a first SCSI bus (BO), a second selected group of said connectors being linked to connect the mass storage devices associated with said second selected group of said connectors to form a second SCSI bus (B1), said first SCSI bus being isolated from said second SCSI bus;

at least one jumper (22) for connecting said first SCSI bus to said second SCSI bus to form a single SCSI bus for accessing all of the plurality of mass storage devices; and

at least one termination board (24c) connected to said single SCSI bus to isolate said 14 single SCSI bus from SCSI buses configured on other SCSI backplanes.

4. The SCSI system of claim 3, further comprising means for associating additional SCSI backplanes with said SCSI backplane so that at least five SCSI buses exist, and wherein said plurality of mass storage devices are

configured in a RAID system.

5. A SCSI system for use in a RAID configuration having a plurality of mass storage devices configured in a specific number of ranks, said SCSI system comprising:

a SCSI backplane having a plurality of connectors, said connectors being interconnected in a specific number of groups each comprising at least one connector, each of said groups corresponding to a separate SCSI bus;

means for decreasing said specific number of groups with a corresponding decrease in a specific number of SCSI buses configured on said SCSI backplane and for increasing the specific number of connectors associated with each SCSI bus by rearranging the configuration of said connectors to decrease said specific number of groups; and

means for isolating each of said separate SCSI buses from all other SCSI buses.

6. The SCSI system of claim 5, further comprising means for increasing said specific number of ranks in said RAID system by configuring additional SCSI backplanes in conjunction with said SCSI backplane.

7. The SCSI system of claim 5, further comprising means for associating additional SCSI backplanes with said SCSI backplane so that at least five SCSI buses exist in said RAID system.

8. A RAID system for organizing the configuration a

plurality of mass storage devices for access by a host computer, comprising:

a housing for securing said plurality of mass storage devices;

a SCSI backplane mounted in said housing, said SCSI backplane having a plurality of connectors, each of said connectors including means for receiving one of said plurality of mass storage devices to connect said one of said plurality of mass

storage devices to a SCSI bus, each of said connectors corresponding to one of a plurality of separate SCSI buses; at least one jumper for connecting a first one of said connectors to a second one of said connectors to configure said mass storage device received by said first one of said connectors and said mass storage device received by said second one of said connectors on a common SCSI bus; and at least one termination board connected to each of said plurality of SCSI buses to isolate each of said plurality of SCSI buses from every other of said plurality of SCSI buses.

9. The RAID system of claim 8, further comprising means for associating additional SCSI backplanes with said SCSI backplane so that at least five SCSI buses exist in said RAID system.