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  Virtual storage devicesUSPTO Application #: 20080109632Title: Virtual storage devices Abstract: Accessing stored data includes providing a virtual storage area having a table of pointers that point to sections of at least two other storage areas, where the virtual storage area contains no sections of data, in response to a request for accessing data of the virtual storage area, determining which particular one of the other storage areas contain the data, and accessing the data on the particular one of the other storage areas using the table of pointers. Accessing stored data may also include associating a first one of the other storage areas with the virtual storage area, where the virtual area device represents a copy of data of the first one of the other storage areas. Accessing stored data may also include causing all of the pointers of the table to initially point to sections of the first one of the other storage areas when the virtual storage area is initially associated with the first one of the other storage areas. The storage areas may be storage devices. The sections may be tracks. (end of abstract) Agent: Muirhead And Saturnelli, Llc - Westborough, MA, US Inventors: Natan Vishlitzky, Haim Kopylovitz, Hana Moreshet, Adi Ofer USPTO Applicaton #: 20080109632 - Class: 711209000 (USPTO) Related Patent Categories: Electrical Computers And Digital Processing Systems: Memory, Address Formation, Address Mapping (e.g., Conversion, Translation), Virtual Addressing, Including Plural Logical Address Spaces, Pages, Segments, Blocks The Patent Description & Claims data below is from USPTO Patent Application 20080109632. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Technical Field [0002] This application relates to computer storage devices, and more particularly to the field of providing copies of portions of data stored on a computer storage device. [0003] 2. Description of Related Art [0004] Host processor systems may store and retrieve data using a storage device containing a plurality of host interface units (host adapters), disk drives, and disk interface units (disk adapters). Such storage devices are provided, for example, by EMC Corporation of Hopkinton, Mass. and disclosed in U.S. Pat. No. 5,206,939 to Yanai et al., U.S. Pat. No. 5,778,394 to Galtzur et al., U.S. Pat. No. 5,845,147 to Vishlitzky et al., and U.S. Pat. No. 5,857,208 to Ofek. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels of the storage device and the storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the storage device directly, but rather, access what appears to the host systems as a plurality of logical volumes. The logical volumes may or may nor correspond to the actual disk drives. [0005] In some instances, it may desirable to provide a copy of a logical volume where the copy is then accessed by other processes. For example, to test new software on actual stored data, a copy of a logical volume containing the data may be made and the copy, as opposed to the original data, may be used to test new software. Once the test is complete, the copy may be eliminated. Thus, the new software is tested on actual data without affecting the actual data. This reduces the likelihood that testing new software and/or functionality will corrupt actual data. [0006] One difficulty with making such copies is that they require as much storage space as the logical volume from which the data is obtained since the copy process simply creates a new volume containing all the data of the original volume. In addition, in some instances, the differences between the original volume and the copy are minimal. Thus, the extra storage space required for such a copy of a logical volume is used somewhat inefficiently since it merely duplicates already-existing data. Accordingly, it would be desirable to provide a mechanism for copying data in a way that uses storage space efficiently. SUMMARY OF THE INVENTION [0007] According to the present invention, accessing stored data includes providing a virtual storage area having a table of pointers that point to sections of at least two other storage areas, where the virtual storage area contains no sections of data, in response to a request for accessing data of the virtual storage area, determining which particular one of the other storage areas contain the data, and accessing the data on the particular one of the other storage areas using the table of pointers. Accessing stored data may also include associating a first one of the other storage areas with the virtual storage area, where the virtual storage area represents a copy of data of the first one of the other storage areas. Accessing stored data may also include causing all of the pointers of the table to initially point to sections of the first one of the other storage areas when the virtual storage area is initially associated with the first one of the other storage areas. Accessing stored data may also include, in response to a write to a first section on the first one of the other storage areas, copying data of the first section to a second section that is on a second one of the other storage areas and causing a corresponding one of the pointers of the table to point to the second section. Prior to copying data from the first section to the second section, the second section may be maintained as a free section containing no data. Accessing stored data may also include maintaining a doubly linked list of all free sections of the second one of the other storage areas. Accessing stored data may also include associating a data indicator with sections of the first one of the other storage areas, where the data indicator for a particular section indicates whether a write operation has been performed to the particular section after the first one of the other storage areas has been associated with the virtual storage area. Accessing stored data may also include, in response to a write to a first section on the first one of the other storage areas and the data indicator indicating that no write operation has been performed to the first section after the first one of the other storage areas has been associated with the virtual storage area, copying data of the first section to a second section that is on a second one of the other storage areas and causing a corresponding one of the pointers of the table to point to the second section. Accessing stored data may also include sending status information to a device that caused the write operation to be performed following copying the data from the first section to the second section. Each of the sections of data may be a track of data. Each of the storage areas may be a storage device. [0008] According further to the present invention, accessing stored data includes providing a first virtual storage area having a first table of pointers that point to sections of at least two other storage areas, where the first virtual storage area contains no sections of data, associating a first one of the other storage areas with the first virtual storage area, where the first virtual storage area represents a copy of data of the first one of the other storage areas at a first point in time, providing a second virtual storage area having a second table of pointers that point to sections of at least two other storage areas, where the second virtual storage area contains no sections of data, associating the first one of the other storage areas with the second virtual storage area, where the first virtual storage area represents a copy of data of the first one of the other storage areas at a second point in time, in response to a request for accessing data of one of the virtual storage areas, determining which particular one of the other storage areas contain the data, and accessing the data on the particular one of the other storage areas using one of the tables of pointers. Accessing stored data may also include causing all of the pointers of the first table to initially point to sections of the first one of the other storage areas when the first virtual storage area is initially associated with the first one of the other storage areas and causing all of the pointers of the second table to initially point to sections of the first one of the other storage areas when the second virtual storage area is initially associated with the first one of the other storage areas. Accessing stored data may further include associating a first data indicator with sections of the first one of the other storage areas, where the first data indicator for a particular section of the first other one of the storage areas indicates whether a write operation has been performed to the particular section after the first one of the other storage areas has been associated with the first virtual storage area, and associating a second data indicator with sections of the first one of the other storage areas, where the second data indicator for a particular section of the first other one of the storage areas indicates whether a write operation has been performed to the particular section after the second one of the other storage areas has been associated with the second virtual storage area. Accessing stored data may also include, in response to a write to a first section that is on the first one of the other storage areas and the data indicator indicating that no write operation has been performed to the first section after the first one of the other storage areas has been associated with the first virtual storage area, copying data of the first section to a second section that is on a second one of the other storage areas and causing a corresponding one of the pointers of the first table to point to the second section. Accessing stored data may also include, in response to a write to a first section that is on the first one of the other storage areas and the data indicator indicating that no write operation has been performed to the first section after the first one of the other storage areas has been associated with the first and second virtual storage areas, copying data of the first section to a second section that is on a second one of the other storage areas and causing a corresponding one of the pointers of the first table and a corresponding one of the pointers of the second table to point to the second section. Accessing stored data may also include, in response to a write to the first virtual storage area corresponding to the second section, copying data from the second section to a third section. Accessing stored data may also include causing a corresponding one of the pointers of the first table to point to the third section. Accessing stored data may also include causing a corresponding one of the pointers of the second table to point to the third section. The first time may be the same as the second time. The first time may be different from the second time. Each of the sections of data may be a track of data. Each of the storage areas may be a storage device. [0009] According further to the present invention, a computer program product includes executable code that provides a virtual storage area having a table of pointers that point to sections of at least two other storage areas, where the virtual storage area contains no sections of data, executable code that determines which particular one of the other storage areas contain the data in response to a request for accessing data of the virtual storage area, and executable code that accesses the data on the particular one of the other storage areas using the table of pointers. The computer program product may also include executable code that associates a first one of the other storage areas with the virtual storage area, where the virtual storage area represents a copy of data of the first one of the other storage areas. The computer program product may also include executable code that causes all of the pointers of the table to initially point to sections of the first one of the other storage areas when the virtual storage area is initially associated with the first one of the other storage areas. The computer program product may also include executable code that copies data of the first section to a second section that is on a second one of the other storage areas and causes a corresponding one of the pointers of the table to point to the second section in response to a write to a first section on the first one of the other storage areas. The computer program product may also include executable code that associates a data indicator with sections of the first one of the other storage areas, where the data indicator for a particular section indicates whether a write operation has been performed to the particular section after the first one of the other storage areas has been associated with the virtual storage area. The computer program product may also include executable code that copies data of the first section to a second section that is on a second one of the other storage areas and causes a corresponding one of the pointers of the table to point to the second section in response to a write to a first section on the first one of the other storage areas and the data indicator indicating that no write operation has been performed to the first section after the first one of the other storage areas has been associated with the virtual storage area. The computer program product may also include executable code that sends status information to a device that caused the write operation to be performed following copying the data from the first section to the second section. Each of the sections of data may be a track of data. Each of the storage areas may be a storage device. [0010] According further to the present invention, a virtual storage device includes at least one table for associating the virtual storage device with a standard storage device, storage for sections of data of the virtual storage device, where a first portion of the storage for sections is sections of data of the standard storage device, and a first plurality of pointers provided with the at least one table, where at least some of the pointers point to sections of the standard storage device corresponding to the first portion. The virtual storage device may also include a second portion of the storage for sections that contain data that is different from data on corresponding sections of the standard storage device that map to the second portion, and a second plurality of pointers provided with the at least one table, where the second plurality of pointers point to sections of a device different from the standard storage device. Each section of the second portion may contain an earlier version of data on a corresponding section of the standard storage device. Each of the sections of data may be a track of data. BRIEF DESCRIPTION OF DRAWINGS [0011] FIG. 1 is a diagram of a storage device used in connection with the system described herein. [0012] FIG. 2 is a diagram of a storage that shows various logical volumes that are used in connection with the system described herein. [0013] FIG. 3 is a diagram showing use of a virtual device according to the system described herein. [0014] FIG. 4 is a diagram showing use of a plurality of virtual devices according to the system described herein. [0015] FIG. 5 is a diagram showing device tables used in connection with the system described herein. [0016] FIG. 6 is a flow chart illustrating reading a table used in connection with a virtual device according to the system described herein. [0017] FIG. 7 is a flow chart illustrating writing to a table used in connection with a virtual device according to the system described herein. [0018] FIG. 8 is a flow chart illustrating modification of a virtual device table and establishing a virtual device according to the system described herein. [0019] FIG. 9 is a flow chart illustrating modification of data structures used to handle tracks of a log device according to the system described herein. [0020] FIG. 10 is a flow chart illustrating steps performed in connection with reading a virtual device according to the system described herein. [0021] FIG. 11 is a flow chart illustrating steps performed by a disk adapter in connection with writing to a standard logical device to which a virtual device has been established according to the system described herein. Continue reading... Full patent description for Virtual storage devices Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Virtual storage devices patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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