GB2343313A - Data storage array using optical data interconnection - Google Patents

Abstract

A data storage array comprises an enclosure having a plurality of data storage devices mounted therein, each of the storage devices including an optical receiver and transmitter. An optical data path is defined within the enclosure by, for example, two mirrors located at opposite ends of the enclosure. The optical receiver and transmitter of each device is positioned in the data path, for transmitting and receiving data to and from the receiver and transmitter of the other storage devices within the enclosure.

Description

DATA STORAGE ARRAY Technical Field of the Invention The present invention relates generally to the field of data storage arrays and in particular to the interconnection of storage devices in such arrays.

Background of the Invention Many current mid to high-end computer systems (e. g. network servers and workstations) include mass storage devices configured as an array.

The array may comprise simply a plurality of disks arranged in an enclosure or alternatively a redundant array (e. g. RAID array) configured to provide fast access to data stored on the devices and also to provide for data backup in the event of a device failure. A RAID array is commonly made up of a number of magnetic disk storage devices, which are held in an enclosure and connected to an array controller function which may take the form of either an array adapter located within the main processing unit of the computer system or alternatively a standalone array controller connected to the main processing unit. The connection between the main processing unit and the array usually takes the form of one of the industry-standard protocols such as SCSI (Small Computer Systems Interface) or SSA (Serial Storage Architecture).

A storage array may be configured in a number of different ways but one common configuration (as used by SSA and FC-AL) places the computer system and array in a loop. The array adapter includes two ports which are connected to opposite ends of a string of storage devices, each of which is packaged in a device carrier in the enclosure. The two ports advantageously provide bidirectional data transfer between the system and the array of storage devices such that if a problem arises with one of the storage devices in the enclosure, it is possible to maintain data transfer to and from the remaining devices of the array.

When the enclosure contains the full complement of device carriers then the data path between one end of the string and the other is complete. However, if the user of the system chooses to populate only some of the enclosure positions with device carriers then it becomes necessary to devise some way of maintaining the interconnections between the device carriers. This creates the need for dummy carriers or some bypass mechanism. However, use of dummy carriers or other mechanisms has the disadvantages of increased electrical noise and degraded data signal quality. They also add unnecessary cost to the machine, particularly in nentry levelrl low cost configurations where a high ratio of dummy carriers to device carriers is required.

An alternative device interconnection arrangement would be desirable which avoids the disadvantages of prior systems such as those which employ dummy carriers as described above.

Disclosure of the Invention According to a first aspect of the invention there is provided a data storage array comprising an enclosure having a plurality of data storage devices mounted therein, an optical data path being defined within the enclosure, each storage device including optical receiver/transmitter means, positioned in the data path, for transmitting and receiving data to and from the receiver/transmitter means of the other storage devices within the enclosure.

In a preferred embodiment the transmitter/receiver means are mounted onto a device carrier which is in turn mounted within the enclosure so as to place the transmitter/receiver means within the optical data path.

In a further preferred embodiment, the storage array includes a pair of optical mirrors located at opposite ends of the enclosure to define a polygonal, e. g. rectangular, optical data path.

Thus, by means of the storage array of the present invention, storage devices can be removed from the optical data path without breaking the connection thus removing the need to provide dummy carriers.

According to a second aspect of the invention there is provided a data processing system including a host computer system connected to a data storage array as defined in the appended claims, the enclosure further including host transmitter/receiver means located in the optical data path for providing communication between the host system and the storage devices.

A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings.

Brief Description of the Drawings Figure 1 shows, in conceptual form, a data processing system comprising a main processing unit connected to a data storage array ; Figure 2 shows an array of data storage devices and dummy carriers in accordance with the prior art ; Figure 3 illustrates a light path employed in a system according to one embodiment of the present invention; Figure 4 shows the light path of Fig. 3 into which is placed a host connection; Figure 5 shows a host connection and storage device positioned in the light path of Figure 3; Figure 6 shows two host connections and a plurality of storage devices according to a preferred embodiment of the present invention; Figure 7 shows a two-loop configuration according to a further embodiment of the present invention.

Detailed Description of the Invention with reference first to Figure 1, there is shown a prior art data processing system including a host computer system 10 having a central processing unit 12 which communicates over a system bus 14 (e. g. PCI) with an array adapter 20. The array adapter includes array management logic 22 for configuring and managing an array 40 of data storage devices 50,52,54,56,58 mounted within an enclosure 60. As used in the following description, the term'storage array encompasses at least redundant arrays such as those configured according to one or more levels of the RAID architecture and also encompasses a group of storage devices arranged as a so-called JBOD (Just a Bunch Of Disks) which do not provide redundancy.

In accordance with one common array configuration (e. g. as defined by the SSA), the connection between array adapter and devices takes the form of a bidirectional loop in which one end of the array of devices is connected to one port 24 of the adapter and the opposite end of the array of devices is connected to a second adapter port 26. As is known in the art, each of the storage devices is packaged into a device carrier which is plugged into a power and signal backplane (not shown). As is indicated conceptually in Figure 1, the data path is complete when the enclosure is fully populated with storage devices. As mentioned previously, when the enclosure is only partially populated with storage devices, dummy carriers 80,82 are required as shown in Figure 2.

Next will be described a preferred embodiment of the invention which avoids the need for dummy carriers in a partially populated enclosure. Figure 3 shows, in schematic form, an enclosure including a pair of mirror units 90,92 arranged at each extreme end. These mirror units provide an optical data path 100 in the shape of a rectangle. It will be appreciated that the optical data path does not have to be rectangular but can instead be any suitable polygonal shape. in Figure 4, there is shown a host carrier 110 inserted into the data path. This host carrier includes an optical transmitter 112 and receiver 114 which are connected via cable 116 to one port of the host adapter of Figure 1. Data and other information transmitted from the host to the enclosure is converted by the optical transmitter into optical signals for transmission over the data path.

As can be seen in Figure 4, the receiver is positioned in the data path to receive optical signals which are converted by the host carrier into electrical signals for communication to the host adapter. The optical transmitter may take the form, for example, of an infra-red or visible LED or solid-state laser. The optical receiver is matched to the transmitter and may take the form of a phototransistor, PIN-diode or similar. The transmitters and receivers employed on the carrier will depend on the host interface environment in which the data storage array is used. For example, ULTRASCSI provides a data rate of 20 MHz, SSA-80 provides a data rate of 200 MHz, SSA-160 provides 400 MHz and FC-AL provides 1000 MHz. All of these data rates may be provided with commercially available transmitter and receiver devices. The host carrier also includes a power connector (not shown) for connection to a power backplane (also not shown) within the enclosure to provide power from the enclosure to the host carrier.

Turning next to Fig. 5 there is shown a storage device carrier 120 positioned in the optical data path of Fig. 4. The device carrier includes an optical transmitter/receiver pair 122,124 identical to those on the host carrier. In the data path, the device transmitter is arranged adjacent to the host receiver and the host transmitter is optically adjacent to the device receiver. The device carrier also includes a data storage device 126 which takes the form of a magnetic disk storage device, although it will be appreciated that the present invention is useful with other types of storage device e. g. optical disk devices or tape drives. As with the host carrier, the device carrier includes a power connector (not shown) for connection to the power backplane of the enclosure in order to provide power from the enclosure to the transmitter/receiver pair and to the data storage device.

It will be seen from Fig. 5 that data is transferred from the host system to the storage device via the host carrier and device carrier. For example, data from the host to be written onto the storage device is converted into an optical signal by the host carrier and transmitted via the optical data path to the device receiver where it is converted into electrical signals and stored on the storage device in the conventional manner. Similarly, data read from the storage device is first converted into optical signals by the device transmitter and transmitted onto the optical data path. The host receiver receives the optical read data and converts it into electrical data for transfer to the host adapter.

It will be appreciated from Figure 5 that by means of the present invention, data communication from the host to a single storage device in the enclosure can be effected without the need for dummy carriers.

Further device carriers can be added to the enclosure simply by inserting the device transmitter and receiver into the optical data path.

Although the principles of the present invention have been explained with reference to Figures 2 to 5, a more typical configuration will be of the type shown in Figure 6 in which a string of eight storage device carriers 120... 190 are positioned in the data path with two host carriers 110,200, each of which is provided for communication with a different host computer. Additional host carriers may be also provided in the data path if desired. Data is transferred between host (s) and devices in the manner described above. If a host wishes to send data to a storage device whose carrier is separated from the host carrier by the device carriers of other storage devices, the data is passed through the optical transmitter and receiver of each intervening device carrier. Suitable device addressing mechanisms which may be used are well known in the art and will not be described further.

It will be appreciated from the foregoing description that host and device carriers can be added and taken away as required without breaking the data path and without therefore requiring the insertion of dummy carriers.

The optical data path shown in Figs. 2 to 6 provides for unidirectional transmission of data. In order to provide a bidirectional duplex system, two instances of the optical data path would be required, for example with one data path located above the other. In this case each host carrier and each device carrier would contain two optical transmitter/receiver pairs.

In Fig. 7 there is shown a further embodiment of the invention wherein the enclosure is further provided with a plug-in mirror unit 250 which allows the storage devices and host computers to be segregated into separate loops 260,270. In Fig. 7 each of the two data paths includes three device carriers and a host carrier.

Although, in the preferred embodiment, the host carriers include the conversion logic necessary for converting between electrical and optical signals it will be appreciated that in an alternative arrangement, the communication between host carrier and host adapter can be optical with the conversion taking place at the host system.

Claims (7)

1. CLAIMS 1. A data storage array comprising an enclosure having a plurality of data storage devices mounted therein, an optical data path being defined within the enclosure, each storage device including optical receiver/transmitter means, positioned in the data path, for transmitting and receiving data to and from the receiver/transmitter means of the other storage devices within the enclosure.
2. 2. A data storage array as claimed in claim 1 wherein each storage device comprises a device carrier on which the optical transmitter/receiver means are mounted.
3. 3. A data storage array as claimed in claim 1 or claim 2 comprising a pair of optical mirrors located at opposite ends of the enclosure to define a polygonal optical data path.
4. 4. A data storage array as claimed in any preceding claim, wherein the optical transmitter comprises an LED or solid-state laser.
5. 5. A data storage array as claimed in any preceding claim, wherein the optical receiver comprises a phototransistor or PIN-diode.
6. 6. A data storage array as claimed in claim 3, further including a plug-in mirror unit located between the pair of optical mirrors to define a first optical data path between a first of the mirrors and the plug-in unit and a second optical data path between a second of the mirrors and the plug-in unit.
7. 7. A data processing system including a host system connected to a data storage array as claimed in any preceding claim, the enclosure further including host transmitter/receiver means located in the optical data path for providing communication between the host system and the storage devices.