Electrical computers and digital processing systems: memory – Storage accessing and control – Specific memory composition
Reexamination Certificate
1998-11-23
2001-10-30
Verbrugge, Kevin (Department: 2187)
Electrical computers and digital processing systems: memory
Storage accessing and control
Specific memory composition
Reexamination Certificate
active
06311251
ABSTRACT:
FILED OF THE INVENTION
This invention relates to data storage subsystems and, in particular, to a virtual data storage subsystem which includes a data storage manager that functions to optimize the data storage utilization in a RAID data storage subsystem that is equipped with a heterogeneous mix of data storage elements.
PROBLEM
It is a problem in the field of data storage subsystems to store the ever increasing volume of application data in an efficient manner, especially in view of the rapid changes in data storage characteristics of the data storage elements that are used to implement the data storage subsystem.
Data storage subsystems traditionally comprised homogeneous collections of data storage elements on which the application data was stored. Within this data storage architecture, it has always been difficult to accommodate data storage elements that differ from those presently in use in the data storage subsystem. The virtual data storage subsystems were more adept at addressing this issue, since the physical data storage elements were mapped into logical devices to present a desired data storage image to the host processors. A popular virtual data storage subsystem architecture is the Redundant Array of Independent Disks (RAID) concept which spread the data set over a set of parallel connected disk drives to emulate the operation of a large capacity disk drive. In this architecture, the disk drives were uniform in data storage characteristics in a selected redundancy group, as a set of the parallel connected disk drives were termed.
An exception to this need for homogeneity in a redundancy group is disclosed in U.S. Pat. No. 5,430,855 titled “Disk Drive Array Memory System Using Nonuniform Disk Drives,” which discloses a data storage subsystem that uses an array of data storage elements that vary in their data storage characteristics and/or data storage capacity. The data storage manager in this data storage subsystem automatically compensates for any nonuniformity among the disk drives by selecting a set of physical characteristics that define a common data storage element format. However, the data storage utilization of the redundancy groups formed by the data storage manager is less than optimal, since the least common denominator data storage characteristics of the set of disk drives is used as the common disk format. Thus, disk drives whose data storage capacity far exceeds the smallest capacity disk drive in the redundancy group suffers from loss of utilization of its excess data storage capacity. Therefore, many data storage subsystems simply configure multiple redundancy groups, with each redundancy group comprising a homogeneous set of disk drives. A problem with such an approach is that the data storage capacity of the data storage subsystem must increase by the addition of an entire redundancy group. Furthermore, the replacement of a failed disk drive requires the use of a disk drive that matches the characteristics of the remaining disk drives in the redundancy group, unless loss of the excess data storage capacity of the newly added disk drive were incurred, as noted above.
U.S. Pat. No. 5,696,934, titled “Method of Utilizing Storage Disks of Differing Capacity in a Single Storage Volume in a Hierarchical Disk Array” discloses a system for utilizing the data storage capacity of a heterogeneous set of disk drives by segmenting the disks into multiple regions. The non-contiguous regions from individual disks are linked to form either a RAID
1
or a RAID
5
logical device. In particular, the system uses two disks of the largest data storage capacity in a redundancy group so that the excess data storage capacity of these two disks is configured as a RAID
1
mirrored disk portion of memory. The remaining segment of the data storage capacity of the largest storage capacity disk drives matches the data storage capacity of the remaining disk drives in the redundancy group and these disk drives are then configured as RAID
5
or other combinations of RAID
1
and RAID
5
. However, this system is limited to the use of the excess data storage capacity of the disk drives as a RAID
1
memory and pairs of the largest storage capacity disk drives must be used in the redundancy group.
Thus, it is a prevalent problem in data storage subsystems that the introduction of new technology is costly and typically must occur in fairly large increments, occasioned by the need for the data storage subsystem to be comprised of homogeneous data storage devices, even in a virtual data storage subsystem. Therefore, data administrators find it difficult to cost effectively manage the increasing volume of data that is being generated in order to meet the needs of the end users' business. In addition, the rate of technological innovation is accelerating, especially in the area of increased in data storage capacity and the task of incrementally integrating these new solutions into existing data storage subsystems is difficult to achieve.
SOLUTION
The above described problems are solved and a technical advance achieved by the present intelligent data storage manager that functions to optimize the data storage utilization in a RAID data storage subsystem that is equipped with a heterogeneous mix of data storage elements. This is accomplished by using preference groups and biasing the writing of stripes of data in the redundancy groups of the RAID system to the disk drive or a set of disk drives in the preference group that have the greatest available data storage capacity. This ensures that the data storage capacity of the the disk drive with the largest available capacity is utilized to the maximum capacity.
A preference group comprises a group of disk drives that is larger than the stripe size that is used to store data in a RAID format. The data storage manager does not write data across all of the disk drives in the preference group at a time, but rotates the collection of disk drives that are used to write a stripe of data. Therefore, if there is a failure of one of the disks in the RAID preference group, only a portion of the stripes stored therein need to be reconstructed, thereby speeding the reconstruction process. By including the the disk drive(s) with the largest available capacity in every stripe that is written to the preference group, the data storage capacity of the disk drive with the largest available capacity is preferentially used in the storage of data, thereby using this excess capacity first, with the utilization of the data storage capacity of this disk drive being related to the ratio of the preference group size to the RAID stripe size.
REFERENCES:
patent: 5430855 (1995-07-01), Walsh et al.
patent: 5542065 (1996-07-01), Burkes et al.
patent: 5574851 (1996-11-01), Rathunde
patent: 5696934 (1997-12-01), Jacobson et al.
patent: 5754756 (1998-05-01), Watanabe et al.
patent: 5860091 (1999-01-01), Dekoning et al.
patent: 6016552 (2000-01-01), Lee et al.
Merritt Perry Wayde
Mullins June
Reeve Ian Fraiser
VonBehren Paul David
Willis Kenneth L.
Bailey Wayne P.
Duft, Graziano & Forest
Song Jasmine
Storage Technology Corporation
Verbrugge Kevin
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