Methods and systems of cache memory management and snapshot operations

• US 20060265568A1
• Filed: 04/19/2006
• Published: 11/23/2006
• Est. Priority Date: 05/16/2003
• Status: Active Grant

• Current Assignee: Oracle International Corporation (Oracle Corporation)
• Original Assignee: Pillar Data Systems, Inc. (Oracle Corporation)
• Inventors: Burton, David Alan
• Granted Patent: US 7,380,059 B2
• Time in Patent Office: Days
• US Class Current: 711/216
• CPC Class Codes: G06F 12/0862 with prefetch
• CPC Class Codes: G06F 12/0871 Allocation or management of cache space
• CPC Class Codes: G06F 12/123 with age lists, e.g. queue, most recently used [MRU] list or least recently used [LRU] list
• CPC Class Codes: G06F 2201/84 Using snapshots, i.e. a logical point-in-time copy of the data
• CPC Class Codes: G06F 2212/284 being distributed
• CPC Class Codes: G06F 2212/285 Redundant cache memory
• CPC Class Codes: G06F 2212/311 In host system

Abstract

The present invention relates to a cache memory management system suitable for use with snapshot applications. The system includes a cache directory including a hash table, hash table elements, cache line descriptors, and cache line functional pointers, and a cache manager running a hashing function that converts a request for data from an application to an index to a first hash table pointer in the hash table. The first hash table pointer in turn points to a first hash table element in a linked list of hash table elements where one of the hash table elements of the linked list of hash table elements points to a first cache line descriptor in the cache directory and a cache memory including a plurality of cache lines, wherein the first cache line descriptor has a one-to-one association with a first cache line. The present invention also provides for a method converting a request for data to an input to a hashing function, addressing a hash table based on a first index output from the hashing function, searching the hash table elements pointed to by the first index for the requested data, determining the requested data is not in cache memory, and allocating a first hash table element and a first cache line descriptor that associates with a first cache line in the cache memory.

Claims

1. A method of destaging data in a stripe in a data storage system, comprising:

receiving a plurality of write commands in a data storage subsystem;

setting a dirty bit for each block of each write in a cache line in a host;

setting a valid bit for each block of each write in the cache line in the host;

locating all of the cache line descriptors for the stripe in the host;

writing the data in the stripe to the data storage subsystem;

acknowledging the data in the stripe is written to the data storage subsystem;

clearing the dirty bits in the host; and

removing the cache line descriptors in the host.

2. The method of claim 1, wherein each of the write commands includes a commands in group field that identifies the writes in the same stripe.

3. The method of claim 1, further comprising writing clean data to the cache of the data storage subsystem for performing a parity computation.

4. A method of prefetching data in a data storage system, comprising:

receiving a first read command from a host requesting data on a data storage subsystem, wherein the first read command includes a prefetch bit indicating data whose addresses are nearby the requested data;

staging the requested data from the data storage subsystem to the host; and

staging the nearby data to a cache of the data storage subsystem.

5. The method of claim 4, further comprising:

receiving a second read command from a host requesting the nearby data; and

retrieving the nearby data from the cache of the data storage subsystem.