Storage Computer Corporation and Another v Hitachi Data Systems Ltd
| Jurisdiction | England & Wales |
| Judge | Mr Justice Pumfrey |
| Judgment Date | 21 August 2002 |
| Neutral Citation | [2002] EWHC 1776 (Ch) |
| Court | Chancery Division |
| Docket Number | Case No: HC 0 1 No 0101244 |
| Date | 21 August 2002 |
[2002] EWHC 1776 (Ch)
IN THE HIGH COURT OF JUSTICE
CHANCERY DIVISION
PATENTS COURT
Royal Courts of Justice
Strand, London WC2A 2LL
The Honourable Mr Justice Pumfrey
Case No: HC 0 1 No 0101244
Simon Thorley QC and Adrian Speck (instructed by Bird and Bird) for the claimants
Peter Prescott QC and James Mellor (instructed by McDermott, Will and Emory) for the defendant
Hearing dates: 18–21, 24–27 June, 1, 2 July 2002
Approved Judgment
I direct that pursuant to CPR PD 39A para 6.1 no official shorthand note shall be taken of this judgment and that copies of this version as handed down may be treated as authentic.
Mr Justice Pumfrey
Introduction
This is an action for infringement of two patents. The validity of both is challenged by the defendant ('itachi'). The patents are concerned with aspects of computer disk torage technology, aspects sufficiently different that it is convenient to consider the wo patents more or less separately, although they share an inventor and have similar itles.
EP 0 294 287 B1 ('287)
'287 is entitled 'Fault tolerant, error-correcting storage system and method for storing igital information in such a storage system'. It is accepted that the claims are entitled to priority from 2 June 1987. The substantial issue is infringement.
This patent is concerned with irrecoverable hard disk-drive errors. Although the invention is stated to be equally applicable to other forms of storage, such as bubble memory and the like, it is principally concerned with disk drives. I shall explain the field of application by reference to hard disks of the kind which were in use for personal computers in 1987, since that is the class of disks with which the patent is particularly concerned. Such disks are often called Winchester disks, after the IBM Research Department at Hursley Park, Winchester, where they were invented. In such disk drives, there is one or more rotating platters made of magnetic material. The rotating platters are notionally divided into concentric tracks, each track being divided into sectors. If there is more than one platter, the vertically aligned tracks are considered to form a 'cylinder".
(Diagram not provided.)
Data is written and read by magnetic heads which fly above the surfaces of the rotating platter, riding on the thin layer of air which is entrained by the rotating object. Normally there are two heads per platter, each head being mounted on an arm which may be moved in and out, towards and away from the hub of the disk, in reliance upon control signals.
The internal electronics of such disks are remarkably complex. By 1987 it was well established that all hard disks intended for personal computers must present one of a comparatively limited number of standard interfaces to the hardware in the computer used to control them. The only such standard referred to in the patent is the so-called SCSI or small computer standard interface. The basic idea is that there is a SCSI controller ('host adapter') in the computer; a SCSI cable connecting the adapter to the drive; and the SCSI drive.
The basic unit of storage of such a drive (at least so far as the host machine is concerned) is the sector. SCSI conceals much of what is actually going on in a disk drive, but the sector will be the minimum amount of data written or read in one go by the drive. The way to address the sectors is by cylinder, head and sector number. The cylinder says how far from the hub: the head identifies the particular platter side, and the sector identifies the particular part of that track.
The SCSI interface is the face that the disk presents to the world. It is not safe to assume that a SCSI disk said to have ( say) 256 cylinders, 64 sectors per track and 8 heads will in fact have such an arrangement internally, but this is what the electronics presents to the world. What: matters is the sector. Every sector read out will be the result of at least one read of a particular sector somewhere in the drive.
Hard disk drives display two types of error, soft errors and hard errors. When a request is made to read or write the contents of a particular sector, the drive may not succeed first time. It will retry the operation a specified number of times. If it succeeds before reaching the maximum number of retries, the error is a soft error, and the drive may deal with it internally. If it fails altogether, that is a hard error. An error signal is returned to the computer, and the operation will have failed. The patent is principally concerned with recovery from hard errors in a particular drive.
At the priority date, there is no doubt that it was well known to deal with hard errors by duplicating disks. Two disks containing duplicate data would be highly unlikely to display a hard error at the same sector. Duplicate disks thus greatly increase data security. The problem with duplication is that the data throughput is halved for every write operation, since two sectors have to be written for every one before. Data throughput for a read operation remains the same as for a single disk, since recourse will be had to the second disk only when the first fails. Professor Maller gave the following evidence in relation to the common general knowledge in the art which was not, I think, challenged:
'3.2.14 Since the number of read/write operations per second, sustainable by an individual disk unit, is limited for purely electro-mechanical reasons and has only risen from approximately 20 in the 1960s to roughly 50 today, it follows that only by using a large number of disks simultaneously can a high transaction rate can be sustained. Logical files can be spread over multiple disk units—a facility which in the early 1980s was known by some people as syndicating. Syndicating offered the possibility of using individual disk channels concurrently to increase both the potential transaction rate, on a particular file, as well as the bulk data transfer rate. This facility could be achieved with exchangeable disk packs, of course, but then the packs, when taken off line, had to be kept together as an entity and, human error being what it is, one of them would be mislaid or used for something else! This idea of syndication on exchangeable disks led to the concept of an array of fixed disks on which files of data would be stored as a set of fixed sized "chunks" with each "chunk" being allocated to a separate disk. This arrangement later became known as striping. However, the term, striping, was not commonly known prior to 1987. Both the number of "chunks" and the stripe depth became parameters which could be chosen to suit particular applications. For example, arrays of fixed disks could be used for: high volume transaction processing: ie a system in which a large number of individual tasks, arrive at a high rate, each of which involves processing only a relatively small quantity of data; eg banking debiting and crediting and airline seat reservation systems (these would generally use a deep stripe of perhaps a disk track or a cylinder so that all the disk activity associated with one user transaction would be localizedon one drive) transferring large volumes of data from individual files at very high speed—an essential requirement in the fields of scientific computation and system simulation; eg weather forecasting or processing satellite data. (In these applications the stripe depth would normally be shallow; eg a single disk sector of perhaps 512 bytes.)
3.2.15 The concept of using multiple disk channels on the same disk drive had already been exploited in those applications where high data transfer rates were required; these ranged from large scientific computations to special purpose high speed machines for searching through large data files. One way of achieving this was by reading several tracks from the same cylinder in parallel (see paragraph [3.2.7] above). However, this technique had become difficult to implement on the highest capacity exchangeable disk units but was much easier on fixed disk units. But as fixed disk units had become a commodity item by the middle 1980s, it was much easier to run the units in parallel as a disk array, having stored the file across them, than to modify them by installing multiple read electronics to perforrrn concurrent multi-head read.
3.2.16 Although striping data across disk arrays gave improved performance, it also had a severe disadvantage: if any one disk failed, the system would fail. The reliability of the system then depended upon the number of disks in the array. The greater the number of disks, the less reliable the system became. So "back-up" was essential to guard against lost data in the event of a disk failure and, in many scientific applications, the files were very large and mirroring would be very costly. "Back— up" was often met pragmatically by using magnetic tape cartridges with a high data transfer rate. In some applications, however, an important requirement was speed in getting the information processed, eg weather forecasting, and the possibility of having to restore a disk from a cartridge tape in the middle of a run would have led to unacceptable delays. People would have had the weather before the forecast was complete! A requirement existed, therefore, for a method of error correction, which could ensure that a disk system could maintain a high average data transfer rate with any errors only causing a momentary hiatus.
3.2.17 The idea of using some form of error correcting code which could operate across an array of disks and correct data in the event of a disk failure "on the fly", as it were, was a topic of discussion and R&D during the mid 1980s, but was not widely known at the time....
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(1) Storage Computer Corporation and Storage Computer UK Ltd and Hitachi Data Systems Ltd
...shall refer to them as Storage. 3 Storage alleged that Hitachi Data Systems Ltd had infringed the patent. Pumfrey J in his judgment ([2002] EWHC 1776 (Ch)) held that the patent was not infringed. He also held that claims 1 and 2 (which stand or fall together) were invalid for obviousness. 4......