Electrical computers and digital processing systems: memory – Storage accessing and control – Specific memory composition
Reexamination Certificate
2001-12-07
2004-04-06
Gossage, Glenn (Department: 2187)
Electrical computers and digital processing systems: memory
Storage accessing and control
Specific memory composition
C711S170000
Reexamination Certificate
active
06718436
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for managing a logical volume for minimizing a size of metadata and dynamic resizing, and a computer-readable recording medium storing a program or data structure for embodying the method; and, more particularly, to a method for managing a logical volume in order to support dynamic online resizing of a logical volume and to minimize the size of metadata managed by the logical volume manager that overcomes a physical limitation of a storage device in computer systems, and a computer-readable recording medium storing a program or data structure for embodying the method.
PRIOR ART
The logical volume manager provides a logical volume which is one virtual disk drive and includes multiple physical disk drives, and implements RAID (Redundant Array of Independent Disks) technique with software to construct the logical volume.
First, RAID and related terms will be explained.
RAID is a way of storing the same data to different locations of multiple hard disks and it is usually utilized in a server with important data. As duplicating and storing the same data to different locations of multiple numbers of hard disks, computing performance is improved by maintaining equilibrium of input/output (I/O) processing and synchronizing input/output processing. Since multiple hard disks increase Mean Time Between Failures (MTBF) and multiple copies of the same data on different locations on the multiple hard disks, fault tolerance of the computer system is also increased despite hard disk malfunctioning.
By placing data on multiple disks, I/O operations can overlap in a balanced way, improving performance. Since the use of multiple disks increases the mean time between failure, storing data redundantly also increases fault-tolerance.
A RAID configuration appears to the operating system to be a single logical hard disk. By utilizing a striping technique in RAID, RAID makes possible varying numbers of partitions within one sector, for example, 512 bytes to several megabytes, on a storage space of hard disks. The stripes of all the disks are interleaved and addressed in order. Striping of all disks may be interleaved and orderly addressed.
In a computer system storing huge data such as a picture in the medical or scientific field, stripes are typically set up to be small size, 512 bytes, so that a single record spans all disks and can be accessed quickly by reading all disks at the same time.
In a multi-user system, better performance requires establishing a stripe wide enough to hold the typical or maximum size record. This allows overlapped disk Input/Output across drives.
There are at least nine types of RAID plus a non-redundant array (RAID-0).
RAID-0: This technique has striping but no redundancy of data. It offers the best performance but no fault-tolerance.
RAID-1: This type is also known as disk mirroring and includes at least two drives that duplicate the storage of data. There is no striping. Read performance is improved since either disk can be read at the same time. Write performance is the same as for single disk storage. RAID-1 provides the best performance and the best fault-tolerance in a multi-user system.
RAID-2: This type uses striping across disks with some disks storing error checking and correcting information. It has no advantage over RAID-3.
RAID-3: This type uses striping and dedicates one drive to storing parity information. The embedded error checking information is used to detect errors. Data recovery is accomplished by calculating the exclusive OR of the information recorded on the other drives. Since an Input/Output operation addresses all drives at the same time, RAID-4 cannot overlap I/O. For this reason, RAID-3 is best for a single-user system with long record applications.
RAID-4: This type uses large stripes, which means records from any single drive may be read. This allows one to take advantage of overlapped Input/Output for read operations. Since all write operations have to update the parity drive, no Input/Output overlapping is possible. RAID-4 offers no advantage over RAID-5.
RAID-5: This type includes a rotating parity array, thus addressing the write limitation in RAID-4. Thus, all read and write operations can be overlapped. RAID-5 stores parity information but not redundant data(but parity information can be used to reconstruct data). RAID-5 requires at least three and usually five disks for the array. It is best for multi-user systems in which performance is not critical or which do few write operations.
RAID-6: This type is similar to RAID-5 but includes a second parity scheme that is distributed across different drives and thus offers extremely high fault- and drive-failure tolerance. There are few or no commercial examples currently.
RAID-7: This type includes a real-time embedded operating system as a controller, caching via a high-speed bus, and has other characteristics of a stand-alone computer. One vendor offers this system.
RAID-10: This type offers an array of stripes in which each stripe is a RAID-1 array of drives. This offers higher performance than RAID-1 but at much higher cost.
RAID-53: This type offers an array of stripes in which each stripe is a RAID-3 array of disks. This offers higher performance than RAID-3 but at much higher cost.
Disk striping will now be explained.
Striping is the process of dividing logically continuous data segments such as a single file and storing the divided segments into physically separated devices such as disk drives using a round robin technique. If a processor has the ability to write and read data faster than to receive and apply data from/to a single disk, striping is a useful technique.
Data is divided into unique sized bytes or sectors and stored over several drives. For example, if there are four drives designed to operate with overlapping read/write operation, generally, four sectors can be read in the same time of reading one sector.
Disk Striping is not provided for fault tolerance or error checking but it can be used for such functions with other techniques.
Striping can be used with mirroring.
Mirroring is a process for duplicating and storing data to more than one device for preventing damaged data in case of malfunctioning devices.
It can be embodied in hardware or software. A RAID system generally has a mirroring function. Operating systems including the Novell Network operating system provide disk mirroring as software. If mirroring is applied to a magnetic tape storage system, it is usually called twinning. Another method, which is cheaper than mirroring, for minimizing data damage is backing up data to magnetic tape at fixed periods.
Based on the above-mentioned terms, the pre-existing technique will be explained in the following paragraphs.
Currently, storage devices with hardware RAID are used for providing better performance, fault tolerance, data recovery from disk error, and to overcome limitations of disk drive size. Such a hardware RAID device has several advantages but it also has an important disadvantage. It is too expensive.
Moreover, it is physically impossible to connect a large number of disk drives as one device so a hardware RAID device also has a limitation of possible applicable storage space.
For overcoming the foregoing problems of the hardware RAID device, a logical volume manager that implements software RAID, has been developed. The logical volume manager is an intermediate level block device driver implementing the various RAID techniques in software based on the calculating ability of a computer, and treats several physically separated independent disk drives as one disk drive.
Pre-existing logical volume managers have been using a fixed mapping method that uses a fixed convert function in converting the logical address used by a high-level module, such as in file systems and general data managers, to a physical address of several underlying physical disk drives. This method has a limitation in flexibility since it fixes the relationship between logical address and physical address. Therefore, it has
Kim Chang-Soo
Kim Gyoung Bae
Shin Bum Joo
Electronics and Telecommunications Research Institute
Gossage Glenn
Jacobson & Holman PLLC
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