Electrical computers and digital processing systems: memory – Storage accessing and control – Specific memory composition
Reexamination Certificate
1999-10-20
2004-05-04
Tran, Denise (Department: 2186)
Electrical computers and digital processing systems: memory
Storage accessing and control
Specific memory composition
C711S004000, C711S170000
Reexamination Certificate
active
06732230
ABSTRACT:
BACKGROUND OF THE INVENTION
In general, the present invention relates to computer storage systems that use multiple disk drives combined into an array of disk drives that ‘appears’ to a host computer as a single logical storage unit that includes fault-tolerance characteristics and yields better overall performance. It has been found that this type of disk array can be made more fault-tolerant by redundantly storing information/data in various ways over the multiple drives, including any of the established RAID (which stands for Redundant Array of Independent Disks) architectures/levels 0 through 5, and subsequent variations/hybrids thereof, whether mapped as hardware- or software-based RAID. More particularly, the invention relates to a new system and unique method for migrating information/data stored on a source volume into a RAID structured assemblage of data carriers whereby a separate back-up disk (or other external storage media) is not needed and the source data carrier can become part of the RAID structured assemblage.
Storage Media, File Systems, Formatting, and Disk Start-up
A storage medium/media can be any data carrier or recording medium into/onto which information (such as data) can be read/copied, such as magnetic (diskettes, hard disks, Iomega's ZIP®/JAZ®/Click!™ disks, tapes, drums, core, thin-film, etc.), optic (CD-ROM, CD-E, CD-R, CD-RW, DVD, and other devices whereby readout is with a light-source and photodetector), and magneto-optic media (media for which optical properties can be changed by an applied magnetic field—used in high end drives). Before data can be written to a storage medium it must be ‘formatted’ (organized and prepared to receive data). In the case of a formatting a disk, a file system is generally ‘burned-in’. Many file system types are currently in use, such as: FAT/FAT16/FAT32 (File Allocation Table) for DOS/Windows 95/98® PC's, HPFS (High Performance File System) used with OS/2 server disks, NTFS (NT File System) used with Windows NT®, ISO 9660 for CD-ROMs, ISO 13346 for DVDs, UDF (Universal Disk Format) for bigger-capacity disks like DVD RAM, Novell's NetWare® server operating system has its own proprietary file system, and UNIX-based servers have their own filing system.
The file system on a disk, for example, operates as an interface between the operating system and the drive in which the disk is located. When a software application, such as MS Word, is asked by a PC user to read a file from a disk, the operating system on that computer engages the file system to open the file. The file name can include a ‘drive letter’ for the drive associated with the disk on which the chosen file is located. Since the file system includes information about physical location of individual files on the hard drive, the file system is engaged to find the relevant physical location on the hard drive, reads the data there, then delivers it to the operating system. During formatting, a disk (such as the hard disk found in a PC's hard drive, Iomega Corporation's portable ZIP®/JAZ®/Click!™ disks, and diskettes) is divided into multi-byte sectors (512-bytes, for example) distributed along concentric ‘tracks’. A hard disk formatted using FAT, for example, has its administrative data stored on an outer track sector(s). Each hard disk, and if partitioned each partition of the disk, often contains four areas in FAT (this depends upon the Partition Type): (1) a boot record, generally in the first sector, (2) FAT administrative data (usually two identical areas), (3) the root directory, and (4) the data area where file information and subdirectories, beyond the root directory, are gathered in clusters (cluster size depends on disk size) locatable by the file system for reading. The formatting of a CD-ROM and a DVD is different as these disks have one-long spiral track divided into identifiable sectors.
A physical hard disk can be divided into different partitions, each of which (for example, in systems running Windows 95® and Windows NT®) can be treated as logically-separate drives. For example, such partitioning of a PC hard drive is usually done by a program called FDISK. A boot record is found on every hard disk (regardless of its specific file system) and contains information about the disk or its partitions. Boot record information enables the file system to handle the disk and also includes a small program used during system start-up. The root directory of a FAT partition is a listing of files and other directories on the respective partition/disk. The root directory of a hard disk with a FAT system, has 512 file or directory ‘entrances’ and is unique from other directories in that it is of a fixed size and is located in the same physical location.
When a hard disk has been partitioned, thus creating each partition into a ‘logical drive’ as perceived by the computer's operating system, the file system must be given information allowing it to recognize this partitioning. Information about the physical location of the beginning and the end of each partition, called the Master Boot Record (MBR)—because it describes the entire hard disk, is stored in the first sector of the physical hard disk. Then, at the beginning of each partition (or, logical drive) is a boot record describing the partition that follows.
Once a computer has been powered-up and its start-up program has finished POST (Power On Self Test) and the loading of BIOS (Basic Input/Output System) routines, the boot process begins. First, the MBR is read and the sector number of the primary partition's boot record is located. Any hard disk that has been partitioned has a primary partition (for example, a drive-letter C: can be assigned) from which booting of the computer takes place and the operating system is read (the small boot program in the primary partition is engaged to activate the loading of the operating system files—which are stored, in a DOS-based PC, as hidden system files in the primary partition).
BRIEF HISTORY OF RAID
In the late-1980's, a paper entitled “A Case for Redundant Arrays of Inexpensive Disks (RAID)” was published by authors from the University of California Berkeley, that described various types of disk arrays. The basic idea of RAID was to combine multiple small, what they deemed ‘inexpensive’ disk drives into an array of disk drives which yields performance exceeding that of a Single Large Expensive Drive (SLED) and is perceived by a host computer as a single logical storage unit or drive. RAID disk arrays, which are interface-independent, are made fault-tolerant by redundantly storing information in various ways. Five types of array architectures, RAID-
1
through RAID-
5
, were originally defined in this paper, each providing disk fault-tolerance. Another level, RAID-
0
, has emerged which is more-correctly a ‘non-redundant’ array of disk drives.
Fundamental to RAID is “striping” of magnetic media, which is a method of concatenating multiple drives into one logical storage unit by partitioning the storage space of each drive in the array into strips (or stripes) which may be as small as one sector of the disk (512 bytes) or as large as several megabytes. These strips are then interleaved round-robin, so that the combined space is composed alternately of strips from each drive. In effect, the storage space of the drive array is shuffled like a deck of cards. Often, the type of application environment in which the RAID is used, I/O or data intensive, will determine whether large or small strips are used.
The ‘Original’ RAID Levels
RAID Level
0
, which is technically not redundant, has data that is split across drives—thus, it's commonly referred to as “striping”—resulting in higher data throughput. Since no redundant information is stored, performance is very good, but the failure of any disk in the array results in data loss. RAID Level
1
provides redundancy by writing all data to two or more drives—thus, it's commonly referred to as “mirroring”. Since one drive is used to store a duplicate of the data, th
Davis Bradley J.
Johnson Stephen B.
Soulier Paul Ernest
Cochran Freund & Young LLC
LSI Logic Corporation
Tran Denise
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