Error detection/correction and fault detection/recovery – Data processing system error or fault handling – Reliability and availability
Reexamination Certificate
2000-04-07
2004-03-02
Iqbal, Nadeem (Department: 2184)
Error detection/correction and fault detection/recovery
Data processing system error or fault handling
Reliability and availability
C711S162000
Reexamination Certificate
active
06701450
ABSTRACT:
TECHNICAL FIELD
The present invention relates specifically, although not exclusively, to data backup and recovery in data processing systems and, in particular, to magnetic tape based data backup and recovery.
BACKGROUND ART
For convenience of description herein, the term ‘computer system’ (or computing apparatus) means an Intel™ microprocessor (or equivalent) based computer system, for example a Pentium™ system, typically operating under an MS-DOS, Windows™ NT or 95/98 operating system environment. Commonly, such a computer system is known as a PC, although the description relates equally to servers, notebooks or laptop computers. It is emphasised, however, that the concepts disclosed herein may be equally applicable to other known, or to be developed, types of computer system. As such, the invention is not intended to be limited to only PC-type systems.
It is well-known to back up data stored on primary storage, such as a hard disk, of a computer system in order to protect against a disaster that might otherwise irrecoverably destroy all or part of the data. Disasters may for example be fire, flood, computer virus or simply accidental deletion of data. One of the main reasons for using magnetic tape as the backup storage medium is that it provides a stable, reliable and relatively cheap option for storing large volumes of backed up data.
Backup application software which executes on the computer system typically provides the functions for enabling such computer system data to be both backed up to, and restored from, tape media, which is written to and read from by a tape drive. Well-known backup application software includes ‘Replica™’ from Stac, ‘ArcServe™’ from Computer Associates, ‘BackupExec™’ from Veritas and ‘Omniback™’ from HP. Well-known tape drives include DDS™ and LTO™ compliant tape drives, both available from HP.
Generally, backup application software comprises one or more computer programs for managing data backup and restore operations on a computer system. Typically, the software provides a user interface, which gives the user the opportunity to select which data, or files, the user wishes to back up. The user may select for backup, for example, all files that have been generated or amended since the last backup, all files in a specific directory (or directories), or simply all files (i.e. the whole hard disk system). In addition, backup application software typically permits the user to schedule backup operations to occur when the computer system is not being used, for example at midnight each night. Then, at midnight each night, the backup application software identifies all the files that need to be backed up and stores the files to tape media in the form of a backup data set. In particular, the backup application software will typically format the backup data set into individual records on tape and precede the data set with some form of proprietary information, for example, identifying the backup application software used, the date of the backup, the time of the backup, etc.
In the event of a disaster, such as hard disk failure or even system destruction, typically, a priority is to rebuild a working system as soon as possible. This requires the computer hardware to be restored to the same state as it was before the disaster, which can take hours or even days, even before the file system can be restored. Generally, a significant amount of human intervention is required to complete this process.
In order to reduce the time and human intervention overhead of restoring a computer system after a disaster, some backup application software provides a so-called disaster recovery (DR) solution, which enables a computer system to be restored in an expedited manner to a state which existed before a disaster occurred. Such a scheme typically involves at least installing and configuring a minimal operating system, tape drivers and the backup application software (or the requisite parts thereof) itself.
Known DR solutions typically require a user to generate a set of DR floppy disks. The DR floppy disks may be used to boot the computer system, when it is not possible to boot from the hard disk drive, and execute application software for recovering a backed-up copy of the file system from tape media. The DR floppy disks typically load and execute a minimal version of the operating system along with components of application software comprising DR functionality, thus providing sufficient functionality, for example, for the computer to build new disk partitions, access a tape drive and restore the data from tape media.
The DR operating system is required to reflect the exact hardware configuration of the computer system on which it is to be installed, otherwise it would not be possible to communicate with storage devices such as tape drives.
Typically, therefore, DR floppy disks need to be regenerated by a user whenever the system hardware configuration changes, and particularly when a SCSI (Small Computer Systems Interface) configuration changes. For example, if a new SCSI Host Bus Adaptor (HBA) is added to a server, with a respective new device driver, this device driver needs to be added to the DR floppy disks so that the new SCSI HBA is recognised when rebuilding the computer system.
Generally, therefore, having ‘current’ DR floppy disks available relies on a user generating them, keeping them up to date, and being able to find them if a disaster occurs. This is an overhead, which sometimes leads to DR floppy disks not being generated at all, disks being allowed to get out of date, or disks being misplaced over time.
A reason why DR floppy disks are used is that a floppy disk-drive is one of the standard ‘initial program load devices’ (IPLD), which practically every PC is configured to ‘boot’ from. Herein, ‘standard’, as applied to an IPLD, implies that the PC is physically programmed to recognise the device for the purposes of booting. Currently, other standard IPLDs, sometimes known as BAIDS (BIOS Aware Initial Program Load Devices), include the first hard disk drive in a PC and, more recently, the first CD-ROM drive in a PC. Generally, however, an IPLD can be virtually any device that has the ability to load and execute a PC operating system.
As already mentioned, it is now possible to boot from a CD-ROM drive, as long as the CD-ROM complies with the ISO 9660 CD-ROM standard, as extended by the ‘El Torito’ Bootable CD-ROM Format Specification, Version 1.0, Jan. 25, 1995, created jointly by IBM Corporation and Phoenix Technologies Ltd. Booting from CD-ROM in a similar manner is also considered in detail in U.S. Pat. No. 5,727,213. As described, to boot from CD-ROM, a PC's BIOS (basic input/output system) needs to specifically support reading boot record data from a CD-ROM, typically, as well as from a floppy disk or hard disk. U.S. Pat. No. 5,727,213 also proposes that tape media may also serve as a boot source, subject to the PC BIOS being modified to detect and read boot record data from a tape media. To date, however, PC BIOS standards do not support booting from tape media.
In a system which is bootable from a CD-ROM, U.S. Pat. No. 5,727,213 specifies that, to read boot record data from a CD-ROM, read commands directed to the floppy disk drive need to re-directed to the CD-ROM drive during a read data part of the boot process. In addition, a modified SCSI driver of the PC needs to convert the 512 byte sectors conventionally used by hard disk and floppy disk into 2 Kbytes sectors conventionally used by a CD-ROM drive.
In view of the possibility of booting from CD-ROM, it would obviously also be possible to generate one or more DR CD-ROMs to replace the DR floppy disks. However, there would be little advantage in adopting this approach, and a significant cost increase. In particular, it would still be onerous for the user to have to generate, maintain and keep safe the DR CD-ROMs.
It is one object of the present invention to provide a more convenient DR solution.
DISCLOSURE OF THE INVENTION
According to a first aspect, the present invention provides a method
Crighton Ian Peter
Gold Stephen
LandOfFree
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