System and method for generating point in time storage copy

• US 20030079102A1
• Filed: 10/22/2001
• Published: 04/24/2003
• Est. Priority Date: 06/01/2001
• Status: Active Grant

• Current Assignee: Hewlett Packard Enterprise Development LP (Hewlett-Packard Enterprise Company)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Korgaonkar, Anuja, Roberson, Randy L., Bean, Robert G., Lubbers, Clark E., Reiser, James M.
• Granted Patent: US 6,915,397 B2
• Time in Patent Office: Days
• US Class Current: 711/202
• CPC Class Codes: G06F 11/0727 in a storage system, e.g. in a DASD or network based storage system drivers for digital recording or reproducing units G06F3/06; circuits for error detection or correction within digital recording or reproducing units G11B20/18; for distributed storage of data in networks, e.g. transport arrangements for network file system [NFS], storage area networks [SAN] or network attached storage [NAS], H04L67/1097
• CPC Class Codes: G06F 11/0772 Means for error signaling, e.g. using interrupts, exception flags, dedicated error registers
• CPC Class Codes: G06F 11/0793 Remedial or corrective actions recovery from an exception in an instruction pipeline G06F9/3861; by retry G06F11/1402; for recovering from a failure of a protocol instance or entity H04L69/40
• CPC Class Codes: G06F 11/1435 using file system or storage system metadata
• CPC Class Codes: G06F 11/1451 by selection of backup contents
• CPC Class Codes: G06F 2201/84 Using snapshots, i.e. a logical point-in-time copy of the data
• CPC Class Codes: G06F 3/0605 by facilitating the interaction with a user or administrator
• CPC Class Codes: G06F 3/0608 Saving storage space on storage systems
• CPC Class Codes: G06F 3/061 Improving I/O performance
• CPC Class Codes: G06F 3/0611 in relation to response time
• CPC Class Codes: G06F 3/0614 Improving the reliability of storage systems
• CPC Class Codes: G06F 3/0617 in relation to availability
• CPC Class Codes: G06F 3/064 Management of blocks
• CPC Class Codes: G06F 3/0647 Migration mechanisms
• CPC Class Codes: G06F 3/065 Replication mechanisms
• CPC Class Codes: G06F 3/0665 at area level, e.g. provisioning of virtual or logical volumes
• CPC Class Codes: G06F 3/067 Distributed or networked storage systems, e.g. storage area networks [SAN], network attached storage [NAS]
• CPC Class Codes: G06F 3/0683 Plurality of storage devices
• CPC Class Codes: Y10S 707/99953 Recoverability
• CPC Class Codes: Y10S 707/99955 Archiving or backup

Abstract

A storage system permits virtual storage of user data by implementing a logical disk mapping structure that provides access to user data stored on physical storage media and methods for generating point-in-time copies, or snapshots, of logical disks. A snapshot logical disk is referred to as a predecessor logical disk and the original logical disk is referred to as a successor logical disk. Creating a snapshot involves creating predecessor logical disk mapping data structures and populating the data structures with metadata that maps the predecessor logical disk to the user data stored on physical media. Logical disks include metadata that indicates whether user information is shared between logical disks. Multiple generations of snapshots may be created, and user data may be shared between these generations. Methods are disclosed for maintaining data accuracy when write I/O operations are directed to a logical disk.

Claims

1. A method of creating a predecessor logical disk that is a snapshot of a successor logical disk, wherein the successor logical disk is defined by user data stored in a plurality of uniquely identifiable PSEGS and by metadata including an L2MAP having a plurality of LMAP pointers, one or more LMAPs including a plurality of RSD pointers, and one or more RDSs having a plurality of PSEG pointers, comprising the steps of:

creating a predecessor PLDMC;

creating an LMAP for the predecessor logical disk;

populating the LMAP for the predecessor logical disk with RSD pointers from the successor logical disk;

creating an L2MAP for the predecessor logical disk;

populating the L2MAP for the predecessor logical disk with the LMAP pointers from the predecessor logical disk;

setting share bits in the LMAPs for the predecessor logical disk and the successor logical disk to indicate that the data is being shared; and

setting share bits in the successor PLDMC to indicate that the data is being shared.

2. A method according to claim 1, wherein the step of populating the LMAP for the predecessor logical disk with RSD pointers from the successor logical disk comprises copying RSD pointers.

3. A method according to claim 1, wherein I/O operations to the successor logical disk are quiesced for a predetermined period of time.

4. A method according to claim 3, wherein the predetermined period of time corresponds to the time required to construct the predecessor logical disk.

5. A method according to claim 1, further comprising the steps of:

receiving a write operation directed to memory located in an identified segment(s) of the successor logical disk;

in response to the write operation, copying the identified segment(s) to the predecessor logical disk; and

executing the write operation in the successor logical disk.

6. A method according to claim 5, further comprising the step of:

clearing share bits in the LMAPs for the predecessor logical disk and the successor logical disk to indicate that the identified segments are no longer being shared; and

clearing share bits in the successor PLDMC to indicate that identified segments are no longer being shared.

7. A computer-based information storage system, comprising:

a pool of physical storage space divided into a plurality of physically addressable memory locations;

a logical disk structure for mapping virtual storage addresses within the logical disk to physically addressable memory locations, the logical disk structure including a plurality of logically addressable RStores and a plurality of logically addressable LMAPs, wherein the LMAPs includes a first memory location for indicating whether a memory segment is shared with a successor logical disk and a second memory location for indicating whether a memory segment is shared with a predecessor logical disk.