MASTER SLAVE
Contents
1. 5 740 397 Sheet 5 of 5 Apr 14 1998 U S Patent 6 0 HHL OL NO UGHLO AHL OL HOLIMS ON SaA UaILNNOD 1400 4014 519165 802415 18 8 OL ANS TANDIJ 5 740 397 1 IDE DISK DRIVE ADAPTER FOR COMPUTER BACKUP AND FAULT TOLERANCE FIELD OF THE INVENTION The present invention relates to a disk drive adapter for a computer system and in particular to an inexpensive high performance high reliability Integrated Drive Electronics IDE disk drive adapter for use with a computer system BACKGROUND OF THE INVENTION A problem which exists in the field of computer systems is the provision of low cost fault tolerant high performance high reliability Integrated Drive Electronics IDE storage with backup capability This problem is further complicated by the present use of a variety of different computer bus architectures requiring different adapters with specific con nectors to be compatible with the varying bus expansion slots To date the inventor is unaware of any single design which accomplishes all the capabilities of a disk drive adapter across the complete spectrum of the many different bus architectures presently in use Computer systems store data on hard disk drives Generally the computer stores2. attempt is made to issue a READ command The disk drive adapter MIR 95 continuously updates the status of the drives A READ command may be directed to the single hard disk drive specified by the user during setup as the default drive from which information should be read If the selected default drive is bad then the status is updated as bad and the disk drive adapter MIR 95 will switch to the working hard disk drive and turn on an audible alarm The disk drive adapter MIR 95 will then transfer the time out status to the IDE host adapter or connector causing the IDE host to retry the command to the working hard disk drive In one embodiment an adapter in accordance with the present invention may be used in a computer system that includes an IDE interface controller and a video monitor The adapter may include means for connecting the adapter to the IDE controller and the video monitor thereby enabling the adapter to monitor information transmitted via the IDE interface controller The adapter may also include means for directing selected data from the IDE controller to the video monitor In another embodiment an adapter in accordance with the present invention may be used in a computer system that includes a motherboard and a plurality of additional boards including an IDE interface controller and a video card or a sound card The adapter may include means for connecting the adapter to the additional boards thereby enabling the adapter to
3. disk drive and a second channel through which information may be trans mitted to the second hard disk drive During start up of the computer the disk drive adapter MIR 95 scans both the first channel and the second channel to determine the number of hard drives attached to each of the two channels If only a single channel is used then all disk operations will be directed to that channel If both channels are used then the disk drive adapter MIR 95 will analyze the hard drives to determine the geometry of the drives cylinders heads and sectors After determining the geometry of the drives the disk drive adapter MIR 95 will determine if the user has specified mirroring operation and will then set up the system accordingly Normal Operations Under normal operations data transmitted by the com puter s CPU will be directed to the host adapter As the disk drive adapter MIR 95 will be connected to the host adapter all information received by the host adapter such as drive track sector transfer size etc will consequently also be received and analyzed by the disk drive adapter MIR 9S After the host adapter provides this information the host adapter will issue a command This command will be intercepted by the disk drive adapter MIR 95 and a BUSY indication will be returned to the host adapter The disk drive adapter MIR 95 will then determine the correct hard disk drive or drives for the transfer of the information issue the comm
4. flowchart illustrated in FIG 4 shows an example of what occurs in a two disk drive system when one of the disk drives is flawed and an attempt is made to write data to both disk drives When a WRITE command is issued to the IDE channel the disk drive adapter MIR 95 monitors the execution of the command and monitors the status of the first and second hard disk drives Data on each of the first and second hard drives is compared prior to the command to determine whether the data on each drive are the same or different If the status of both drives is the same then mirroring is confirmed both the first and second hard drives are identi fied as functioning properly and the same data is written to both drives On the other hand if the status of both drives is not equal then it is assumed that a problem exists and a process is initialized to determine the extent of the problem The disk drive adapter MIR 95 then goes to a time out counter to retry the hard drive status check a predetermined number of times If during this time out check the disk drive adapter MIR 95 determines that the status of both drives is in fact equal then it assumes that the problem has been corrected The disk drive adapter MIR 95 then updates the status of the drives and writes data to both drives in accordance with the standard mirror mode procedure as previously described On the other hand if the status of the drives remains consistently unequal during the tim
5. is made to read data from a disk DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description is of the best presently contemplated mode of carrying out the invention This description is not to be taken in a limiting sense but is made merely for the purpose of illustrating the general principles of the invention The scope of the invention is best defined by the appended claims FIGS 1 and 2 show an example of a disk drive device or adapter MIR 95 in accordance with the present invention connected via a first channel to a first drive comprising a master and slave drive and via a second channel to a second drive also comprising a master and slave drive as well as to an IDE host adapter system board not illustrated In the illustrated embodiment the connection between the disk drive adapter MIR 95 and the IDE host adapter board is via a standard 40 44 pin IDE connector A 1 and associated flat cable Element A 2 represents a first register stack In the illustrated embodiment six registers are provided for cap turing disk transfer information as the information is being written to the drive registers Logic in the disk drive adapter referred to herein as MIR 95 will elect one of the drives from which to read data Data read by the host adapter will come directly from the elected drive The logic may be provided by a chip such as the Altera PLD 8032 or 8232 for example Standard TTL Logic may be
6. pro vided by 74 245 74LS373 74F04 Element A 3 represents a second register stack including a seventh and eighth register These registers accept the command register data sent by the host adapter and provide the status register information that is read by the host adapter A control unit A 4 is provided for monitoring drive operations selecting the drive to provide data to be read by the host adapter and provide the user interface for error indication and device configuration In the illustrated embodiment a first or primary channel 5 supports both a first master drive and a first slave drive A second or mirrored channel A 6 supports both a second master drive and a 10 15 20 25 35 45 55 65 6 second slave drive making a combined total of four drives The function of monitoring the operation of the drives and controlling the user interface are performed by a microcon troller A 7 Element A 8 represents a user interface unit which allows a user to configure the disk drive adapter MIR 95 and monitor the status of the first hard drive or the second hard drive Start up Each time the computer is started a check is made by the disk drive adapter MIR 95 to determine the serviceability of the first hard disk drive and the second hard disk drive This may be accomplished in the following manner The disk drive adapter 95 has a first channel through which information may be transmitted to the first
7. to the IDE host controller while taking information from the IDE host connector The present invention provides a single piece of hardware which may be used to achieve mirroring in any system using an IDE interface The present invention thereby eliminates the need to use a different kind of mirroring hardware for every different type of computer interface ISA PCI The present invention does not require a direct connection to the bus and is not restricted to use with a particular type of bus Attaching an adapter in accordance with the present invention to the IDE host connector allows the disk drive adapter MIR 95 to monitor all the information being transmitted between the host adapter and the hard disk drive including READ commands and WRITE commands because the set of registers A 2 are identical to the set of registers on the hard disk drive The flowcharts shown in FIGS 3 5 illustrate examples of disk activity and monitoring processes that occur when an 10 15 25 35 45 50 55 65 8 adapter in accordance with the present invention is installed in a personal computer In the illustrated example the disk drive adapter MIR 95 is attached on one side to an IDE connector on the system board or a separate IDE adapter and on the other side to at least one hard disk drive The flowchart illustrated in FIG 3 shows an example of how the disk drive adapter MIR 95 may monitor and update the status of the hard d
8. to occupy 3 5 floppy disk bay in the computer a 5 25 floppy disk bay Alternatively the disk drive adapter may be configured to use one of the ISA slots next to the initial IDE connector for power and maintenance capabilities 5 740 397 5 The user interface may consist of a serial channel or a front panel display and keypad The disk drive adapter may be configured to indicate a drive failure visually or audibly thereby allow the user to schedule required maintenance BRIEF DESCRIPTION OF THE DRAWINGS A detailed description of a preferred embodiment of the present invention will be made with reference to the accom panying drawings FIG 1 shows an example of a disk drive adapter in accordance with the present invention connected to two hard disk drives and an IDE adapter system board via a standard 40 44 pin IDE connector FIG 2 shows an example of the detailed hardware con figuration of the disk drive adapter shown in FIG 1 FIG 3 shows an example of how an adapter in accordance with a preferred embodiment of the present invention may monitor and update the status of the hard disk drives determining whether the drives are functioning and whether the drives are performing a mirroring function FIG 4 shows an example of what may occur in a two disk drive system when one of the disk drives is flawed and an attempt is made to write data to both disk drives FIG 5 shows an example of what may happen when an attempt
9. use the copy of the data on the other unit of that mirrored pair until the broken unit is repaired or replaced and its copy of the data is rebuilt Generally this method is described as the RAID 1 system The term RAID Redundant Array of Independent Disks means a disk array in which part of the physical storage capacity is used to store information about user data The redundant information enables regeneration of user data in the event that one of the array s member disks or the access path to it fails A more detailed discussion of RAID systems is found in a book entitled The RAID Book A Source Book for RAID Technology published Jun 9 1993 by the RAID Advisory Board Lino Lakes Minn RAID level 1 or disk mirroring offers the highest data reliability by providing one to one protection in that every bit of data is duplicated and stored within the storage system This activity occurs automatically as data is input into the system The ability of a mirrored storage system to protect against situations where data can not be accessed such as when data is destroyed due to a head crash or when data is temporarily unavailable due to a component failure and the way the automatic switch between a failed drive and a good drive occurs is directly related to the way the hardware is connected the way the disk units are arranged in mirrored pairs and often is dependent on specific software In the second or parity method as
10. N HOST CONNECTOR PIN HOST READ REGISTER 7 HOST READ REGISTER 8 CONTROL SIGNALS CONTROL SIGNALS Advertisement for GS Model 11 051 Model 18 and GSI Model 21 Accelerator Boards by GSI Inc and bearing a Copyright date of 1993 1994 1 page Silicon Valley Computer advertisement bearing a date of Jan 21 1994 CompuTechnology Group press release bearing a date of Apr 18 1993 3 pages DC Series User s Manual IDE E Z Raid 1 Feb 28 1994 Coffee Peter Micron PC redresses Pentium faluts video disk subsystems give PowerStation strong showing across benchmark suite PC Week Ziff Davis Pablishing Com pany Feb 28 1994 Primary Examiner Jack Harvey Assistant Examiner ligar Pancholi Agent or Firm Loeb amp Loeb LLP 57 ABSTRACT An adapter for use in a computer system having an IDE interface controller and a plurality of drives The adapter is connected to the IDE controller and the plurality of drives and monitors information transmitted between the IDE interface controller and the plurality of drives The adapter determines whether each of the plurality of drives is viceable and whether data on each of the plurality of drives are equal Identical data is directed to each of the plurality of drives when data on each of the plurality of drives are equal Data is prevented from being directed to at least one of the plurality of drives when data on each of the
11. United States Patent Levy US005740397A 5 740 397 Apr 14 1998 Patent Number Date of Patent 154 DISK DRIVE ADAPTER FOR COMPUTER BACKUP AND FAULT TOLERANCE 75 Inventor Itzik Levy Hollywood 73 Assignee ARCO Computer Products Inc Hollywood Fla 21 Appl No 540 765 Oct 11 1995 22 Filed 51 Int acid ccna canteens GO6F 11 16 52 U S 395 441 395 182 04 58 Field of Search 395 441 182 04 56 References Cited U S PATENT DOCUMENTS 7 1980 Schmidt 1 1991 Dunphy Jr et al 4 989 206 1 1991 Dunphy Jr et al 5 051 887 9 1991 Berger et al 5 167 032 11 1992 Martin et al 5 185 884 2 1993 Martin et al 5 212 784 5 1993 Sparks 5 239 659 8 1993 Rudeseal et al 5 303 244 4 1994 Watson 5 333 277 7 1994 Searls 5 345 565 9 1994 Jibbe et al 5 379 417 1 1995 Lui et al 5390327 2 1995 Lubbers et al 5 392 244 2 1995 Jacobson et al 5 408 634 4 1995 Joho 5 418 925 5 1995 DeMoss et al OTHER PUBLICATIONS Wong Willaim PC Upgrade How to Build Your Own Raid Drive Array System vol 6 No 2 Jun 1997 Silicon Valley Computer IDE Mirror Controller Card for IBM AT 286 386 amp 486 Compatible Systems User Manual Copyright 1992 by Silicon Valley Computer 4 213 177 4 989 205 DATA BUS BANK 40 44 PIN REGISTERS FLAT CABLE REGISTER R REGISTER 40 44 PI
12. and or commands to those disk drives and return information from the hard drives to the host adapter If the command is a single drive command for example a READ command then the disk drive adapter MIR 95 will select the appropriate hard drive and will immediately return status and interrupt information from that hard drive to the host adapter If the command is a two drive command for example a WRITE command then the disk drive adapter MIR 95 will direct the command to both the first and the second hard drives In this fashion information provided by the CPU will be replicated on two disks thereby providing automatic substantially simultaneous backup against loss of data A READ command is an example of what in this context may be referred to as a one drive command whereas a WRITE command is an example of a two drive command In other words information is only read from one drive whereas information may be written to both drives Drive Error The disk drive adapter MIR 95 is designed so that it can detect a failure in any of the attached drives By repeatedly checking the status of the drives it will determine if the status of both the first hard drive and the second hard drive is the same indicating normal operation As mentioned above under normal operation the status and interrupt information will be returned to the host adapter If the status of the two hard drives is not equal then the disk drive adapter MIR 95 will determi
13. d to mirror information under existing designs must act as the initial IDE connector to the system bus via an expansion slot of specific design or a connector on the bus A PCI adapter will only fit a PCI bus a VL bus adapter will only fit a VL bus etc It is an object of the present invention to provide a hardware solution to the problem of optimal mirroring while achieving higher performance higher data availability and lower cost It is another object of the present invention to enable the implementation of substantially automatic substantially instantaneous RAID 2 disk mirroring under IDE or EIDE thereby providing a mirroring data protection scheme which is less expensive than under SCSI It is another object of the present invention to prevent downtime when a disk failure occurs It is another object of the present invention to provide a disk drive adapter designed to function as an intermediate 10 15 30 35 45 55 65 4 adapter connectable to an existing IDE connector thereby eliminating the need to use an expansion slot It is another object of the present invention to provide a disk drive adapter designed to function with any operating system presently available on the market such as DOS Windows UNIX Novell OS 2 or any future operating system which supports the IDE interface SUMMARY OF THE INVENTION In accordance with the present invention these and other objectives are achieved by providing a c
14. data by writing the entire data file onto a single disk drive A hard disk controller or adapter provides the logical link between the hard drive and the other peripherals attached to the computer The hard disk controller reacts to requests from a Central Processing Unit CPU by sending seek read write and control signals to the drive and must integrate and control the flow of data The failure of a single disk drive can result in the loss of a significant amount of data In order to minimize the possi bility of such data loss hard disk drives are built to be highly reliable units Nevertheless disk crashes still occur The speed reliability and processing capability of com puter systems are constantly being improved thereby allow ing users to handle more complex and sophisticated appli cations Such improvements in computers impose greater performance and reliability demands on mass storage and Input Output I O devices The mass storage industry has sought to improve I O performance and to provide access to stored data at levels of high reliability See for example The RAID Book A Source Book for RAID Technology published Jun 9 1993 by the RAID Advisory Board Line Lakes Minn As personal computers have become more of a mass market product storage devices are required which meet these goals in a cost effective manner Designers of mass storage systems seek to optimize cost per megabit performance and high data availabilit
15. e method of claim 6 comprising the step of gener plurality of drives when data on each of the plurality of ating an audible alarm when data on each of the plurality of drives are not equal and drives are not equal selecting one of the plurality of drives as a drive from which to read data
16. e of claim 1 comprising means for generating an audible alarm when data on each of the plurality of drives are not equal 3 The device of claim 1 wherein the computer system includes at least one of a 3 5 floppy disk bay and a 5 25 floppy disk bay and wherein the adapter is configured to occupy at least one of the 3 5 floppy disk bay and the 5 25 floppy disk bay 4 The device of claim 1 wherein the computer system includes an ISA slot and wherein the adapter is configured to be received in the ISA slot 5 The device of claim 1 wherein the means for connect ing the adapter to the IDE interface controller and the plurality of drives comprises a 40 44 pin IDE interface connector 6 In a computer system including at least an IDE connector a pre existing IDE interface controller on a motherboard and a plurality of drives a method comprising providing an adapter connecting the adapter via the IDE connector simulta neously to both the IDE interface controller and to the plurality of drives monitoring information transmitted between the IDE interface controller and the plurality of drives determining whether each of the plurality of drives is serviceable determining whether data on each of the plurality of drives are equal directing identical data to each of the plurality of drives when data on each of the plurality of drives are equal 5 740 397 11 12 preventing data from being directed to at least one of the 7 Th
17. e out check then it is assumed that a fatal error has occurred and one of the drives is bad The disk drive adapter MIR 95 may identify which of the two drives is bad by determining which drive is providing feedback and which drive is failing to provide any feedback The drive providing no feedback is identified as the bad drive 5 740 397 9 The disk drive adapter MIR 95 then automatically switches from a mirror drive mode to a single drive mode and turns on an audible alarm which alerts the user to the fact that only one drive is working The disk drive adapter MIR 95 identifies the non working drive as the bad drive and prohibits information from being written to or read from the bad drive switching all commands to the functioning hard disk drive Apart from this change the disk drive adapter MIR 95 continues to allow information to be written to and read from the working drive and the user may continue to work at the computer as if no error had occurred The disk drive adapter MIR 95 goes back and updates the status and continues to monitor the one good drive rather than both the good and bad drives An attempt may there after be made to make the drives equal again either through software or hardware or by manually repairing or replacing the bad disk drive While FIG 4 shows an example of what may happen in a two disk drive system when an attempt is made to issue a WRITE command FIG 5 shows an example of what may happen when an
18. f the bus type The present invention offers a RAID1 disk mirroring solution to all existing and future systems using the IDE interface without requiring dedicated software Data mirror ing into two or more different drives attached to the disk drive adapter is obtained substantially as the data is written without adding extra device transfer time beyond that required to find the desired disk area on each of the drives In the event that one of the drives fails the disk drive adapter is capable of immediately switching all operations to an alternative working drive without requiring user interven tion A drive failure will therefore not require data recon struction In a preferred embodiment the invention can mirror information between channels from two to four drives which represents the current IDE limitation due to definition and cable connectors However if the ability of IDE were to increase the number of drives on the IDE channel then present invention would also be able to address the increased number of drives A disk drive adapter in accordance with the present invention is thereby capable of providing IDE disk mirroring to at least two identical or non identical drives independent of computer model operating system or bus technology The user may choose between reading data from the first drive or reading data from the second drive or sharing the reading of data between both drives The disk drive adapter may be configured
19. isk drives determining whether the drives are functioning and whether the drives are performing a mirroring function This monitoring function may be performed for READ commands WRITE commands or other relevant disk actions Depending on the number of hard disk drives attached and the related setup the disk drive adapter MIR 95 can determine whether the system is in a single disk drive mode or a mirrored disk drive mode As shown in FIG 3 when a command including for example a READ command a WRITE command or a SEEK command is issued a check is made to determine whether the system is operating in a mirror mode that 15 using more than one drive or in a non mirror mode using only one drive A non mirror mode might be operative for example when one of two or more hard disk drives has failed or when only one disk drive is present or when the computer operator has intentionally decided to use only one drive even though more than one drive may be present The disk drive adapter MIR 95 monitors the system to determine which mode the system is in If the disk drive adapter MIR 95 determines that the system is not in a mirrored disk drive mode then it essentially functions as a standard IDE adapter On the other hand if the disk drive adapter MIR 95 determines that the system is in a mirror mode then for each WRITE command it will cause the same data to be written to all of the hard drives rather than to only one hard drive The
20. ly more expensive than IDE hard disk drives SCSI adapters are also more expensive than IDE adapters Though the description above only briefly highlights some differences between the IDE and SCSI interfaces they are considered very different for a technical implementation One can not connect a SCSI adapter to an IDE drive or vice versa The mirroring of information into two or more disk units requires an expert understanding of the physical connections of the hardware so that the hardware path from the disk units to the system can be duplicated or mirrored and to ensure a high degree of protection by reducing the number of single hardware failure points Pairing up disk units must take into account other system and mirroring restrictions such as compatibility with operating systems bus technology conflicting software assuring that the disk units of a mirrored pair are independently operational etc Pairing of disk units for mirroring is difficult time consuming and error prone It can frequently result in invalid configurations or configurations of less than optimal pairing and protection There are several bus technologies utilized in personal computer systems for example ISA VESA local bus EISA PCI local bus and MCA There is no single IDE mirroring solution that applies to all such bus technologies Each mirroring solution requires a dedicated hardware design and related software Consequently the few existing adapters use
21. monitor information transmitted via the additional boards The adapter may also include means for directing selected data from the additional boards to a computer peripheral In still another embodiment an adapter in accordance with the present invention may be used in a computer system that includes a motherboard and a plurality of additional boards including for example an IDE interface controller a video card a modem card and a sound card The adapter may include means for connecting the adapter to the addi tional boards thereby enabling the adapter to monitor infor mation transmitted via the additional boards The adapter may also include means for directing selected data from the additional boards to a computer peripheral The adapter may also include means for directing selected data from the additional boards regardless of bus architecture and operat ing systems Although product names of several specific circuit ele ments used in preferred embodiments of the present inven tion have been identified herein it is recognized that any 10 15 20 45 55 65 10 circuit element chip which performs functions similar equivalent to the components described here may be sub stituted with no change in the functionality of the invention The present invention is therefore not limited to the specific circuit elements identified herein and changes in such circuit elements may be made to accommodate such con sideration
22. ne if the error is a 5 740 397 7 fatal error or a recoverable that is correctable error If the error is determined to be recoverable then the disk drive adapter MIR 95 will return the status of the failed drive to the host adapter so that the host adapter can take normal corrective measures If the error is not recoverable then the disk drive adapter MIR 95 will remove the failed drive from service switching all disk activities to the working channel and signal the user of a fatal error In a diagnostic mode the user can rebuild hard drives or determine if all drives are in working condition Preferred Embodiment A typical personal computer in use today has one drive one controller and a 40 44 pin IDE connector A primary goal of the present invention is to protect data by writing the data to a second drive If the first drive fails then a complete set of data is immediately available on the second drive In a preferred embodiment of the present invention this is accomplished adding an additional hard drive and posi tioning the disk drive adapter MIR 95 between the existing drive and the new hard disk drive and the 40 44 pin IDE connector Instead of writing information to only one drive the same information is written to both drives The user interface reveals only one of the two drives unless the user intentionally wants to see both drives For example with the disk drive adapter MIR 95 attached to the IDE host connect
23. ognizes several hard disk drive storage interfaces including for example ST506 412 ESDI SCSI IDE ATA ATA 2 and EIDE While all of these interfaces are available to manufacturers in the personal computer industry the most commonly used 5 740 397 3 interfaces the Small Computer System Interface SCSI and the Integrated Drive Electronics Enhanced Integrated Drive Electronics IDE EIDE There are significant differences between SCSI technol ogy and IDE technology in terms of design speed and cost SCSI based on an original design by Shugart Associates is a method of allowing different devices to communicate within a PC The entire controller is built on the component PCB Fully integrated parallel data is transferred to and from a PC by way of a single cable through a bus interface that has configured a disk drive device The SCSI interface communicates to the host computer via a protocol which allows multiple types of devices printers drives tape backup scanners etc to connect and function together SCSI implementations include disk drives tape printers removable drives and many other peripherals In comparison IDE a technology developed originally by Compaq and Conner relies on the register level com mand sent by the computer using INT 13 routines Com munications between the drive and the controller flow on a 40 pin flat cable IDE is a relatively simple interface SCSI hard disk drives are considerab
24. omputer system generally containing a disk drive adapter a preferred embodiment of which is referred to herein as MIR 95 connected to an IDE disk controller The IDE disk controller is connected to a bus The computer may have one of a variety of different buses A disk drive adapter in accordance with the present invention is designed to be connected directly between the IDE interface controller hereinafter also referred to as the IDE host or IDE host controller and at least two different hard drives The IDE host adapter may be in the form of any IDE adapter any IDE connector provided by a system board or any external IDE interface Information will therefore flow between the disk drive adapter in accordance with the present invention and the mirrored pair of hard disk drives via the IDE disk controller Use of the adapter in this configuration will allow the user to keep the existing IDE disk controller protecting the hardware investment A disk drive adapter in accordance with the present invention is thereby designed to function as an intermediate adapter connectable to an existing IDE connector thereby eliminating the need to use an expansion slot This design allows the user to keep the existing controller around which all drivers and applications are installed Since there is no need to use an expansion slot the bus technology of the particular computer becomes irrelevant This allows for functionality by one adapter regardless o
25. or a user employing a DOS operating system will see only a C prompt indicating the hard disk drive C is specified even though data will be directed to two mirrored hard disk drives The disk drive adapter MIR 95 performs the function of learning what the host adapter is trying to do either a READ command or a WRITE command and directing data to one drive or to both drives Upon receipt of a WRITE command the disk drive adapter MIR 95 will write the data coming from the host adapter to both drives The data will thereby be duplicated simultaneously Upon receipt of READ command the disk drive adapter MIR 95 will choose the drive from which the date will be read The data is not required to go through the disk drive adapter MIR 95 The disk drive adapter MIR 95 merely selects the drive that will be participating in the READ or WRITE information flow Processors which could support the activi ties of a device in accordance with the present invention would include either an 8 or 16 bit processor such for example the Intel 8031 or 80286 Because an adapter in accordance with the present inven tion takes data from the IDE host connector the present invention achieves mirroring without requiring the modification removal or replacement of the system IDE host controller or the use of specialized mirroring software and or hardware The present invention enables the system IDE host controller to remain intact and simply connects
26. plurality of drives are not equal One of the plurality of drives is selected as a drive from which to read data 7 Claims 5 Drawing Sheets MIR 95 NIT CONTROL U 5 740 397 Sheet 1 of 5 Apr 14 1998 U S Patent LINQ IOWLNOD 46 T 14 QIYOS 5 8 5 740 397 Sheet 2 of 5 Apr 14 1998 U S Patent 0 gt 2 m 3AV IS YALSVW INN 1041100 1 6 STIVNOIS 1 8 318163 LSOH 2 4315193 4 LSOH YOLOANNOD LSOH Nid 9 43151034 5 4315103 15193 8 3151033 20 43151034 1 315193 543151934 ANVE STVNDIS Vivd 1 0 1 13 Nid 77 JHNH 5 740 397 Sheet 3 of 5 Apr 14 1998 U S Patent 9 5 740 397 Sheet 4 of 5 Apr 14 1998 0 5 Patent 502418 aLwddn awa sw NO 5 8 29 TENNWHO JO 5010418 TS HLOd OL ANS LNO FAIL arvad AJILNACI OML
27. s as cost reduction lack of allocation of components or other reasons The presently disclosed embodiments are to be considered in all respects as illustrative and not restrictive the scope of the invention being indicated by the appended claims rather than the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein What is claimed is 1 An adapter for use in a computer system the computer system including at least an IDE connector a pre existing IDE interface controller on a motherboard and a plurality of drives the adapter comprising means for connecting the adapter via the IDE connector simultaneously to both the IDE interface controller and the plurality of drives and for enabling the adapter to monitor information transmitted between the IDE inter face controller and the plurality of drives means for determining whether each of the plurality of drives is serviceable means for determining whether data on each of the plurality of drives are equal means for directing identical data to each of the plurality of drives when data on each of the plurality of drives are equal means for preventing data from being directed to at least one of the plurality of drives when data on each of the plurality of drives are not equal and means for selecting one of the plurality of drives as a drive from which to read data 2 The devic
28. sociated with RAID levels 2 5 a portion of the storage area is used to store redundant data but the size of the redundant storage area is less than the remaining storage space used to store the original data Other arrangements include backing up only the most critical data stored on the disk drive or periodically backing up the data that is stored on the disk drive by storing it on much less expensive data storage unit that also has a much slower data retrieval access time When backup systems utilize technologies other than hard disk drives these other arrangements may not offer the same high level of confidence of data integrity because the media surface may be exposed to outside contamination rather than being self contained such as a disk drive which is hermeti cally sealed These non mirroring arrangements usually also require the computer to be dedicated to a non productive task backup directly opposing the purpose of the computer which is to increase and or enhance produc tivity Further if the back up media is not rigid for example if the back up is made on magnetic tape then it is subject to stretching and other related deficiencies These conditions combined with the continuing reduction of fixed disk cost delineate backup functioning as a dedicated task vs backup as an non dedicated task with dedicated being antiquated and not a cost efficient method of data protection Present personal computer technology rec
29. y The performance of present hard disk I O systems includ ing the hard disk controllers is limited Data stored on hard disks is located by the comparatively slow process of seeking and disk rotation related to the data requests Because the hard disk drive is a mechanical device it is an inherently slower and less reliable component than one based on a solid state design such as a computer circuit board High data availability is the ability to recover data stored in the storage system even though some of the data has become inaccessible due to disk failure or some other reason and the ability to assure operation in the event of such failure When data becomes unavailable or the data stored on the disk drive is lost such occurrence can cause significant disruption in the operation of the personal com 10 15 25 35 55 65 2 puter and the business of the operator thereby creating the need for fault tolerant solutions Present computer technology recognizes several solutions to disk fault tolerance Two methods of storing redundant data are most commonly used According to the first method which may be referred to as the mirror method data is duplicated and stored in two separate areas of the storage system For example a computer system that uses disk mirroring keeps identical copies of data on a pair of disk units designated as mirrors of one another If one disk unit in a mirrored pair fails the system can
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